Martina Flatscher
email: martina.flatscher@zf.com

Andreas Riel
email: andreas.riel@grenoble-inp.fr

Innovation Driver New Production Technologies: Strategic Planning using Technology Roadmapping

Keywords: Strategic Foresight, Strategic Agility, Technology Roadmapping, Innovation Management for Manufacturing, Strategic Production Planning, Roadmapping Process, Decision Support

As innovation cycles are becoming shorter and technological progress faster, the need for reliable decision support for product and production planning is rapidly gaining crucial importance. To this aim, strongly innovation-driven industries like automotive use roadmaps relating products and technologies to a timeline from a specific company's viewpoint. Technology-driven manufacturing companies are struggling to apply technology roadmapping in a transparent, traceable and risk-minimizing way to plan their future production technology and competence needs. This paper points out the necessity of a holistic and integrated approach to using this instrument to help prepare organizations for new manufacturing processes and technologies in a timely and successful manner. It investigates the state of the art of technology roadmapping for strategic production planning, and derives necessary fields of action in the context of an industrial research and innovation project.

Introduction

Manufacturing industries are confronted with exceptional challenges in period which is frequently called the "fourth industrial revolution". Modern manufacturing paradigms such as Added-Value Manufacturing and Knowledge-based Manufacturing are mainly characterized by the fact that modern production is increasingly driven by integrated information technology (IT) systems, rendering manufacturing systems more autonomous, flexible and configurable. At the same time, the megatrend environmental sustainability is driving new manufacturing technologies and processes at a speed that has never been experienced before. Additive manufacturing and lightweight materials processing are only two representative examples for those drivers which are confronting manufacturing industries with new and complex challenges.

This paper was presented at The XXVI ISPIM Conference -Shaping the Frontiers of Innovation Management, Budapest, Hungary on 14-17 June 2015. The publication is available to ISPIM members at www.ispim.org.

2

More than ever before these industries will have to invest early in the building up of know-how and infrastructure to implement manufacturing processes, and adapt them timely both to the rapid technology development and ever changing product requirements. Industries are therefore looking for tools helping them plan production technology investments timely and reliably. The challenge is to prepare technology development as good as possible, to anticipate changes and to implement actions timely in addition to cover the ground. However, industrial organizations seeking to drive product, service and process innovation also by their manufacturing technologies and processes are looking for a methodological support for what we want to call strategic production planning (SPP) in the following.

This article investigates the relevance and use of technology roadmapping (TRM) for this purpose from the particular point of view of a large German tier-1 automotive supplier. Section 2 explains the requirements to a production technology planning instrument from a practical point of view, with a particular regard on related innovation management aspects. Section 3 presents a bibliometric analysis based literature review on TRM and identifies the particular challenges linked to the use of this instrument for SPP. Section 4 provides an insight into an industrial research project introduced in this paper that has been launched with the aim to fill some major gaps that currently render TRM difficult to use for production technology planning. Finally, the paper concludes by a summary and an outlook on the objectives of the industrial research project.

Production technology planning needs

In order to explain the challenges associated with production technology planning in the context of innovation management, we want to point out the necessity of a methodological support for SPP in industrial organisations seeking to drive innovation also by their manufacturing technologies and processes. These organisations aim at integrating production technology planning into their innovation management processes. Innovation management in production wants to make the production fit for the future. In order to capture the numerous dependencies this process has, it makes sense to distinguish between the activity groups related to strategic production planning, the actual content of SPP and the specific innovation areas in the SPP (Figure 1).

In the SPP, many assets and activities are associated with the innovation planning of a holistic production, especially the trend management and hence the consideration of internal and external requirements. Many external and internal inputs that influence the production have to be reflected adequately. There are aspects of the internal requirements coming from the production constraints, foreign locations, strategy, investment, and so on. Moreover the proper handling of trends in the production is critical, because trends often refer only to the product without drawing conclusions about the manufacturing of these products. In addition to that, the active procurement and capitalization on external inputs (e.g. external analysis of production topics) is often not carried due to lack of resources made available to this aim. Mostly this is the consequence of poor management attention to pro-active innovation management for the production. A key question is therefore how to guarantee an optimal SPP to identify fields of action in the production in the context of production specific trends.

In all the mentioned activities and especially in content of SPP, there is a need of interaction with many sub-systems such as machine planning, production system design, international location and layout planning. Furthermore activities regarding research, strategic operational business, development, innovation management, etc. have to be agreed upon the stakeholders. In every step of SPP various stakeholders within the production and from neighbouring areas have to be involved systematically. At this stage the SPP is methodologically supported by strategic considerations in different dimensions. Tools such as the portfolio tool (do we produce and assemble internally or externally?) and the roadmap (how do we produce?) can help in the SPP. The technology roadmap hedges a suitable use of production technologies, e.g. to achieve the goal of an optimal degree of automation in the production and the development of skills and competences in the production whereas a production portfolio can improve the connection between foreign locations and make or buy decisions concerning production planning aspects.

On the operational level an appropriate idea management with respect to an adequate trend management is important to ensure the right use of strategic tools with the right topics. Innovations in the SPP can happen especially on the basis of the active management and implementation of new production technology ideas that are dynamically positioned in the roadmap according to a defined process and taking into account clearly defined criteria (e.g. the technology's alignment with the company strategy, its core competencies and corporate image). Considering the example of the trend topic lightweight construction, ideas have to be generated to find materials, technologies and related production methods that lead to weight reduction. This, however, also implies to think about how and when to build up methodological competences around these topics, as well as material expertise.

Figure 1 Strategic production planning as a fundamental element of innovation management in production [START_REF] Flatscher | The Need for a Structured Approach towards Technology Roadmaps in Innovation-driven Industries, Systems, Software and Services Process Improvement[END_REF] Consequently innovation in the SPP is successful if it succeeds in getting the organization engaged in right topics with the right actions at the right points of time. In that manner the SPP ensures innovative approaches such as the suitable use of production technologies, dealing with new technologies, building of competences and skills, as well as an innovative production planning. In all mentioned findings dependencies between SPP elements and tools exist and are complex.

This paper was presented at The XXVI ISPIM Conference -Shaping the Frontiers of Innovation Management, Budapest, Hungary on 14-17 June 2015. The publication is available to ISPIM members at www.ispim.org.

A literature review of technology roadmapping

TRM is an effective tool for technology planning and coordination which fits within a broader set of planning activities [START_REF] Garcia | Fundamentals of Technology Roadmapping[END_REF]. Motorola was the first to publish about the use of a technology roadmap from the viewpoint of a practitioner [START_REF] Willyard | Motorola's technology roadmap process[END_REF]. As a further industrialist, Philips Electronics confirms the technology roadmap as tool for better integration of business and technology strategy [START_REF] Groeneveld | Roadmapping Integrates Business and Technology[END_REF]. Over the last few years, roadmapping has been a gaining momentum as a strategic management tool for organisations to better adapt themselves to modern marketplaces [START_REF] Gerdsri | Roadmapping as a Strategic Tool to Survive Today's Marketplace[END_REF] or even to strengthen the competitiveness in aligning the development of several technologies [START_REF] Schuh | Roadmapping for Competitiveness of High Wage Countries[END_REF]).

There is a set of different roadmaps with different purposes such as forecasting, planning, and administration [START_REF] Lee | Customization of technology roadmaps according to roadmapping purposes: Overall process and detailed modules[END_REF][START_REF] Gerdsri | Mapping the knowledge evolution and professional network in the field of technology roadmapping: a bibliometric analysis[END_REF][START_REF] Vatananan | The Current State of Technology Roadmapping (TRM): Research and Practice[END_REF][START_REF] Buczacki | Influence of regional planning methods for planning processes in companies[END_REF]. The most generic roadmap consists of layers such as market, product and technology spanning over a horizontal timeline. In these layers, the evolution of the competition, markets, products, technologies as well as the relationships between these factors are depicted [START_REF] Eirma | Technology roadmapping -delivering business vision, Working group report[END_REF]. The synchronisation of all relevant planning levels leads to a holistic, aligned technology planning. However, there is no methodological support of the consideration of interdependencies between planning objects and no dynamic, transparent visualisation for relevant planning situations [START_REF] Orilski | Development of a reference model for dynamic, data based technology roadmapping[END_REF]). The formalised roadmap process is composed of the three phases: preliminary activity, development, and follow-up activity [START_REF] Willyard | Motorola's technology roadmap process[END_REF]. The architecture of a roadmap consists of a planning horizon and key milestones (Phaal et al. 2003a).

A systematic literature review published by Carvalho et al. shows that the principal academic journals that discuss TRM are in the field of "Technology Forecasting and Social Change" and "Research-Technology Management". Thus the use of roadmapping for forecasting plays an important role, largely because of the alignment between strategic objectives and technology management [START_REF] Carvalho | An overview of the literature on technology roadmapping (TRM): Contributions and trends[END_REF]. Furthermore it is possible to anticipate, identify, and confirm changes in industry and technology to spot market, technology and research gaps [START_REF] Garcia | Fundamentals of Technology Roadmapping[END_REF][START_REF] Mcmillan | Roadmapping Agent of change[END_REF]Phaal et al. 2003b;[START_REF] Garcia | Introduction to Technology Roadmapping: The Semiconductor Industry Association's Technology Roadmapping Process, Unlimited Release No[END_REF][START_REF] Paci | An approach to open mapping of research based manufacturing[END_REF]. The incorporation of knowledge of patterns of technological evolution into technology roadmaps makes it possible to detect opportunities for innovation and possible market limitations [START_REF] Rinne | Technology roadmaps: Infrastructure for innovation[END_REF]. A crucial condition hereby is an adequate technology assessment when creating the roadmap [START_REF] Herrmann | Automotive After-Sales Technology and Innovation Management -Technology Assessment and Roadmapping for Automotive Services[END_REF].

A major objective of the TRM process is to come up with a support for technology investment decisions. Often it is not clear which alternative to pursue, how quickly a new technology will be adopted on the market, or when there is a need to coordinate the development of multiple technologies [START_REF] Garcia | Fundamentals of Technology Roadmapping[END_REF]. In this case roadmapping provides information to make better technology investment decisions in identifying critical technologies and gaps and therefore ways to leverage R&D investments (Ahlqvist et al. 2013). Linking R&D investment strategies to business leads to strategic technology alignment roadmapping [START_REF] Gindy | Linking R&D investment strategies to business needs: Strategic Technology Alignment Roadmapping (STAR)[END_REF][START_REF] Gindy | Strategic technology roadmapping STAR® aligning R&D investments with business needs[END_REF].

Ioannou et al. insist on the importance of the fact that for TRM to be successful, the strategic decision-making process has to be a collaborative one [START_REF] Ioannou | Roadmapping as a collaborative strategic decision-making process: shaping social dialogue options for the European banking sector[END_REF]. By its very nature, roadmapping is a mediating and networking approach [START_REF] Miller | Mediating instruments and making markets: Capital budgeting, science and the economy[END_REF]. The activation of network can be the integration of supplier in the roadmap as innovative collaborative networks building [START_REF] Goenaga | Strategic roadmaps as a key driver for collaborative innovation networks design and coordination. A case study[END_REF] or a crossfunctional approach to product and technology planning and vision building [START_REF] Lee | Customization of technology roadmaps according to roadmapping purposes: Overall process and detailed modules[END_REF] or the ongoing coordination between the corporate laboratories and the business units [START_REF] Kappel | Perspectives on roadmaps: How organizations talk about the future[END_REF]. Because of many affected people there are synergies among team members from different departments [START_REF] Gerdsri | Dynamics of technology roadmapping (TRM) Implementation[END_REF]) and more members including both technical and commercial functions such as R&D, product development, manufacturing, marketing, finance, and human resources [START_REF] Albright | Roadmapping in the corporation[END_REF]Phaal et al. 2003b).

In considering the roadmap as a networking approach the outcome is a consensus building process, which connects an expected future (descriptive) with a desired future (normative) [START_REF] Zweck | Technology roadmapping: turning hype into a systematic process[END_REF]. This consensus building succeeds because of the possibility in roadmapping to create a breakdown from a master business roadmap all the way to a technology introduction plan on the strategic level. These plans are further refined at the tactical level, and finally completed into separate project plans for implementation [START_REF] Hakkarainen | Strategic management of technology -from creative destruction to superior resilience[END_REF]. With the adequate management attention in the roadmapping process, the roadmap team will be motivated to do good work by considering several options, addressing management's key concerns, and justifying their positions with a clear rationale [START_REF] Kappel | Perspectives on roadmaps: How organizations talk about the future[END_REF]. Their participation will increase because it is known that the output would be used in funding decisions, noting that participants and the attention of decision makers were involved in the roadmapping effort [START_REF] Kappel | Perspectives on roadmaps: How organizations talk about the future[END_REF]. Thereby the roadmap permits the investigators to then gather evidence about key decisions and their consistency [START_REF] Kappel | Perspectives on roadmaps: How organizations talk about the future[END_REF]. This is especially important for decision aids to improve the coordination of activities and resources in increasingly complex and uncertain environments [START_REF] Kostoff | Science and Technology Roadmaps[END_REF]. TRM must therefore deal with challenges of knowledge and collaboration [START_REF] Ioannou | Roadmapping as a collaborative strategic decision-making process: shaping social dialogue options for the European banking sector[END_REF]. In order to make sure that both the operational and strategic technology decision making succeed it is important to provide a framework to structure diverse information of simultaneously explicit data and the tacit knowledge [START_REF] Petrick | Roadmapping as a mitigator of uncertainty in strategic technology choice[END_REF].

As a decision support instrument, roadmapping is also a means of risk identification, quantification, and mitigation. A so called risk-aware roadmapping supports an appropriate treatment of uncertainty and risk and delivers the identification, resolution and communication of uncertainties and risks. This includes a conscious and explicit effort to address uncertainty and risk and the necessary mitigation steps and procedures [START_REF] Ilevbare | An investigation into the treatment of uncertainty and risk in roadmapping: a framework and a practical process[END_REF].

One particular important aspect of technology planning is the sourcing of new technologies in terms of building up of new competencies to bridge foreseeable technology gaps. Hereby it is necessary to align technology and competencies within an overall roadmap [START_REF] Gokhale | Technology and competence alignment to the Roadmap[END_REF], which gives the opportunity for a company to identify new core capabilities and competencies to focus on [START_REF] Barker | Technology foresight using roadmaps[END_REF]. As a dynamic strategic practice it constructs and fosters relevant future-oriented knowledge that builds on the systemic understanding of the 'grand challenges'. This knowledge will be linked with actual strategic practices in the organization converting future information towards future knowledge [START_REF] Ahlqvist | Constructing futures knowledge: roadmapping as a dynamic strategic practice[END_REF], arising structural relationships among science, technology, and applications [START_REF] Kostoff | Science and Technology Roadmaps[END_REF]. In supporting the strategic business planning and thus the evaluation of different opportunities or threats, gaps are identified at the business level, by comparing the future vision with the current position, and strategic options explored to bridge the gaps [START_REF] Phaal | Technology roadmapping -A planning framework for evolution and revolution[END_REF]). An

This paper was presented at The XXVI ISPIM Conference -Shaping the Frontiers of Innovation Management, Budapest, Hungary on 14-17 June 2015. The publication is available to ISPIM members at www.ispim.org.

integrated TRM methodology enables the management to define its technology requirements, taking into account financial and other issues, to assess proposed technology projects against these requirements and to create a balanced technology project portfolio. The thereby gained improved clarity and transparency of decisions makes it easier to justify the assignment of resources to technology assessment [START_REF] Gindy | Technology roadmapping for the next generation manufacturing enterprise[END_REF]).

As a logical path creator from strategy to implementation roadmapping provides a treatment in strategic, tactical, explicit and operational tier [START_REF] Hakkarainen | Strategic management of technology -from creative destruction to superior resilience[END_REF]. Thereby a master roadmap can summarizes an entire strategy of a business securing highly sensitive and confidential information and generalization of more detailed and focused maps. Specific roadmap responsible persons have full freedom and consequent responsibility to plan and execute their developments and actions, provided they do not contradict, or have side effects on, the master roadmap level [START_REF] Hakkarainen | Business Model Roadmapping. A Practitioner's Approach[END_REF]. Thereby it simultaneously captures explicit data and the tacit knowledge [START_REF] Petrick | Roadmapping as a mitigator of uncertainty in strategic technology choice[END_REF]. Thus roadmapping offers a process to support a holistic technology management. There are early activities like technology foresight and strategy development as well as controlling of individual projects until they fully impact the company's profitability [START_REF] Lischka | Technology roadmapping for manufacturing: a case study at Siemens AG[END_REF].

While the roadmap is fairly simple in structure and concept, its content is the result of processes that involve considerable levels of complexity detail [START_REF] Phaal | Technology Roadmapping: Linking Technology Resources to Business Objectives[END_REF]. Implementing these processes and measuring their performance represents a huge challenge for organizations. They are compelled to evaluate the technique's value and its return on investment in terms of the effectiveness of the outcomes. This includes quality control of data and information used in the TRM process [START_REF] Vatananan | The Current State of Technology Roadmapping (TRM): Research and Practice[END_REF].

Another challenge is the difficulty to keep the roadmapping process 'alive' on an ongoing basis [START_REF] Vatananan | The Current State of Technology Roadmapping (TRM): Research and Practice[END_REF][START_REF] Lee | An analysis of factors improving technology roadmap credibility: a communications theory assessment of roadmapping processes[END_REF]. Approaches are needed to knowing how and when to review and update a roadmap and how to effectively maintain and improve the roadmapping process once it is integrated into day-to-day operations [START_REF] Eirma | Technology roadmapping -delivering business vision, Working group report[END_REF]. There is a lack of practical guidelines for all roadmapping steps, and in particular for the regular update of an already implemented roadmap [START_REF] Garcia | Fundamentals of Technology Roadmapping[END_REF][START_REF] Phaal | Technology roadmapping -A planning framework for evolution and revolution[END_REF][START_REF] Farrukh | Industrial practice in technology planningimplications for a useful tool catalogue for technology management[END_REF][START_REF] Lee | Technology roadmapping for R&D planning: the case of the Korean parts and materials industry[END_REF].

A key success factor is the establishment of a collaborative network to ensure a dynamic 'alive' roadmapping process. This is typically a difficult task that requires a lot of efforts [START_REF] Goenaga | Strategic roadmaps as a key driver for collaborative innovation networks design and coordination. A case study[END_REF]. There are many surveys investigating which stakeholders to involve in roadmapping and how [START_REF] Vatananan | The Current State of Technology Roadmapping (TRM): Research and Practice[END_REF][START_REF] Kappel | Perspectives on roadmaps: How organizations talk about the future[END_REF][START_REF] Gausemeier | Stakeholder based innovation management[END_REF]. They point out that stakeholders are often not well aware of the usefulness of the roadmap and sometimes even resist following because of the negative consequences for the degree to which the technology roadmap is used and continuously maintained [START_REF] Lee | An analysis of factors improving technology roadmap credibility: a communications theory assessment of roadmapping processes[END_REF][START_REF] Nakamura | A roadmapping practice for enhancing the Japanese engineering service towards advanced IT network age[END_REF].

Towards a systematic process-based approach to roadmapping

This last finding pointed out in the previous section summarizes the major conclusions that we can draw from our literature analysis of TRM: The theoretical body underlying the TRM practice is surprisingly sparse, in general and in particular for production technology. Only very few articles addressing the topic of a systematic approach to planning investments into and deployment of modern manufacturing technologies in a way that industrial organizations get an actionable guidance to deploying production technology planning successfully. Most of the articles use a roadmap as a tool to visualize or manage individual targets such as trends and research challenges in sustainable manufacturing and not to provide methodological approaches to support firms to be flexible in trend handling in the holistic production. Nakamura et al. argue that an academic approach based on a theoretical foundation is necessary to fill the gaps that exist between the potential of TRM and its actual usefulness in existing organisations [START_REF] Nakamura | A roadmapping practice for enhancing the Japanese engineering service towards advanced IT network age[END_REF]. So far, the evolution of roadmapping as a strategic decision support tool has been led by management practice rather than by management theory [START_REF] Phaal | Developing a technology roadmapping system[END_REF][START_REF] Holmes | The application of operation and technology roadmapping to aid Singaporean SMEs identify and select emerging technologies[END_REF]. Only Lichtenthaler provides a contribution to opening up TRM to take into account the increasing importance of external technology commercialization and thereby establish successful strategic technology planning processes in the context of open innovation [START_REF] Lichtenthaler | Opening up strategic technology planning: extended roadmaps and functional markets[END_REF].

Based on the major conclusions above and in the context of a recently launched collaborative research project, we are addressing the challenge of how to approach strategic innovation planning systematically from a production technology point of view and designing and investigating a roadmapping process whose specific objective is to support SPP in close cooperation with the strategic product and procurement planning. This roadmapping process consists in three steps from megatrends towards actions/project sheets. The concretization level increases towards the actions. Concrete actions are than visualized in a roadmap. The process is on a rolling one year basis. At the heart of this approach is the systematic and regularly collaboration of key stakeholders from different organizational units and departments (research and development, production technology, procurement, site planning, etc.) in moderated ideation workshops. The workshops take place regularly every 3 months and different moderation techniques are applied depending on the concretization level of the process stage. In the whole innovation management in the production, shown in Figure 1, and especially in the initial stage of trend management the open way of problem solving proposed by Geschka, can be used as fundamental process element. The first divergent thinking step identifies trends with a very wide open angle of view. Hereby out-of-thebox thinking is the major objective. Then followed is a consolidation phase where methods for finding convergence are applied. Here, the major objective is to process relevant trends in a way that topics can be prioritized and production specific trend can be identified [START_REF] Geschka | Das Offene Problemlösungsmodell (OPM) und andere Problemlösungsstrategien, Preiß L[END_REF].

Conclusion

Production Technology Planning is exposed to numerous interdisciplinary dependencies especially to the product planning, which makes the process complex. In this context strategic roadmapping is an important and common used means for product and technology planning in the several industry sectors, most notably the automotive sector. Unfortunately roadmapping of products and product technologies in common practice is often done with only few links to the roadmapping of production and production technologies, which leads to the fact that companies perform sub-optimally with respect to the speed and timeliness of build-up of new expertise such as new production technologies. The ever increasing speed of technological progress and changes determines a huge potential of improving competitive advantages by mastering the This paper was presented at The XXVI ISPIM Conference -Shaping the Frontiers of Innovation Management, Budapest, Hungary on 14-17 June 2015. The publication is available to ISPIM members at www.ispim.org.

integration of production technology planning with product / service planning better than competitors do.

One key contribution of this paper is the revealed need for such activities, and the investigated state of the art of TRM as a facilitating tool for strategic production planning. Our key finding of the bibliometric analysis based literature review on TRM is that very few publications give practically usable instructions and/or best practice experience reports of how to set up, implement and deploy roadmapping successfully. In particular, we could not find explicit treatment of TRM for SPP in literature. Given that roadmaps are an important and widely used means of product and technology planning, we are convinced that roadmapping can also provide a considerable support in strategic production planning.

The recently launched collaborative industrial research project introduced in this paper aims at establishing a systematic TRM process for SPP on a pilot project level. Beyond the roadmapping process itself, a particular challenge will be to extend the scope from pure technology planning to an integrated strategic planning of technologies and their associated competencies, infrastructures, and deployment in the organization and the products and services delivered. At the heart of this supportive approach is the systematic collaboration of key stakeholders from strategic product and procurement planning in moderated ideation workshops. These workshops take the involved stakeholders from technological, societal, economical and ecological megatrends to their specific impact on the company from the viewpoint of production technology in relationship with products and strategic company evolution objectives.

This paper was presented at The XXVI ISPIM Conference -Shaping the Frontiers of Innovation Management, Budapest, Hungary on 14-17 June 2015. The publication is available to ISPIM members at www.ispim.org.

This paper was presented at The XXVI ISPIM Conference -Shaping the Frontiers of Innovation Management, Budapest, Hungary on 14-17 June 2015. The publication is available to ISPIM members at www.ispim.org.


Dr David Pierrot

Dr Marc Presset

Prof. Dr Jean Rodriguez

Dr Damien Bonne
email: damien.bonne@univ-amu.fr

Dr Yoann Coquerel
email: yoann.coquerel@univ-amu.fr

Normal, Abnormal, and Cascade Wittig Olefinations of α-Oxoketenes

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

a-Oxoketenes are densely functionalized, highly reactive, electrophilic reaction intermediates of past and current great interest, not only because of mechanistic and theoretical considerations, but also because of their rich chemistry as building blocks in organic synthesis. [1] With very few exceptions, they cannot be isolated under ordinary conditions and must be generated in situ. The two most convenient and commonly employed methods for the generation of a-oxoketenes are the thermal decomposition of dioxinones, [2] and the thermal or photochemical Wolff rearrangement of 2-diazo-1,3-dicarbonyl compounds. [3] For the work described herein, and based on some precedents with simple ketenes, [4] it was considered that unsymmetrically functionalized a,a'-bisoxoallenes, for example, 4 a-f, a class of chiral molecules difficult to obtain and only available through relatively complex multistep synthetic sequences, [5] could be readily prepared by a Wolff rearrangement/Wittig olefination cascade reaction from diazo compounds and carbonyl-stabilized ylides via intermediate a-oxo-ketenes. Several examples of the anticipated a,a'-bisoxoallene synthesis could indeed be realized. However, in a number of cases the reaction between a-oxoketenes and carbonyl-stabilized ylides followed alternative pathways involving either abnormal Wittig olefinations or cascade normal/abnormal Wittig processes to afford 4H-pyran derivatives. In this article, we report in full detail the results of our experimental and theoretical investigations on the synthetically valuable chemical dichotomy in the reactions of a-oxoketenes with carbonyl-stabilized Wittig ylides.

Results and Discussion

Our investigations started with the acyclic diazo compounds 1 a-c, which were allowed to react with the representative Wittig ylides 2 a-c in toluene at 140 or 170 8C under microwave irradiation conditions promoting rapid, quantitative, and regioselective (when applicable), Wolff rearrangements of the diazo compounds 1 into the corresponding a-oxoketenes 3 (Scheme 1). [1e-h] As expected, the desired a,a'-bisoxoallenes 4 a-f were obtained in fair to good yields, unlocking the practical synthesis of this valuable class of compounds. As an interesting observation, we also found evidence for the formation of a minor amount of g-pyrone 5 l (15 %) in the reaction between diazo 1 a and ylide 2 a. The formation of 5 l can be rationalized by invoking a 1,4-C-electrophilic/O-nucleophilic behavior of the a-oxoketene 3 a triggering an abnormal Wittig olefination (see mechanistic discussion below). [START_REF]For the previous reports describing isolated examples of an "abnormal Wittig olefination[END_REF] g-Pyrones are valuable chemical moieties with a relatively frequent occurrence in biologically active natural and non-natural products. [7] Existing synthetic methods forging g-pyrones are often of limited breadth, hampering the exploration of their potential in chemistry and chemical biology, [7,[START_REF] J‰ger | For approaches to di-or trisubstituted g-pyrones involving inverse electron demand hetero Diels-Alder reactions with a-oxoketenes[END_REF] and alternative methods are desirable.

Stimulated and intrigued by these early results, a series of representative in situ generated a-oxoketenes were allowed to react with a selection of carbonyl-stabilized Wittig ylides. It was actually found that a-oxoketenes generally react with ketone-stabilized, and to some extent aldehyde-stabilized, ylides 2 via abnormal Wittig olefinations rather than regular Wittig olefinations, which resulted in the synthesis of polysubstituted and functionalized monocyclic and fused bicyclic g-pyrones 5 a-k in fair to good yields (Scheme 2). The a-oxoketene intermediate derived from 2-diazo-1,3-cyclohexanone (1 d; R 1 , R 2 =-(CH 2 ) 3 -) reacted with the methyl ketone-stabilized Wittig ylide 2 d (R 3 = Me) to afford the fused bicyclic 4H-pyran-4-one 5 a in 69 % yield, the structure of which was confirmed by Xray diffraction analysis. Similarly, 4H-pyran-4-ones incorporating either an alkyl (in 5 b), hindered alkyl (in 5 c, 5 d and 5 i), phenyl (in 5 e), carbethoxyl (in 5 f), or carbethoxymethyl (in 5 g) substituent, or a simple hydrogen atom (in 5 h) at the 6 position, could be prepared. The reaction with the non-symmetric diazo ketoamide 1 c (R 1 = NMe 2 , R 2 = Me) afforded exclusively the 2dimethylamino-functionalized 4H-pyran-4-one 5 j in 74 % yield, following a regioselective Wolff rearrangement of the diazo compound. A variation of the reaction was used for the preparation of the 4H-pyran-4-one 5 k having the 3 position unsubstituted (R 2 = H), which involved the thermolytic decomposition of 2,2,6-trimethyl-4H-1,3-dioxin-4-one (1 h) for the generation of the required monosubstituted a-oxoketene intermediate. [2] In a control experiment, the irradiation with microwaves of a toluene solution of the diazo compound 1 e (R 1 , R 2 = -CH 2 C(CH 3 ) 2 CH 2 -) and the phosphorous ylide 2 d for 15 minutes at 80 or 130 8C (which are temperatures that do not or only slowly promote the Wolff rearrangement of 1 e) left the starting materials essentially unchanged, showing that the ylide is inert toward the diazo compound at these temperatures. Overall, a simple and rapid synthetic method to prepare diversely substituted and functionalized 4H-pyran-4-ones has been discovered, revealing that the abnormal Wittig olefination is not just a laboratory oddity [START_REF]For the previous reports describing isolated examples of an "abnormal Wittig olefination[END_REF] but a general reaction. It nicely complements existing methods to synthesize g-pyrones. [7,[START_REF] J‰ger | For approaches to di-or trisubstituted g-pyrones involving inverse electron demand hetero Diels-Alder reactions with a-oxoketenes[END_REF] Notably, ynol ethers have in the past been reported to undergo inverse-demand Diels-Alder cycloaddition with a-oxoketenes to regioselectively afford g-pyrones of type 5 having an alkoxide R 3 substituent. [8c,d] As to the complementary method reported herein, the Wittig ylides 2 a,d-h may be regarded as synthetic equivalents of terminal alkynes capable of undergoing regioselective [4+ +2] cycloaddition reactions with a-oxoketenes (Scheme 3).

In sharp contrast to the above results, the combination of the a-oxoketene derived from the diazo 1 e and the ester-stabilized Wittig ylide 2 c did not produce the a,a'-bisoxoallene 4 g or the g-pyrone 5 m, but the 4H-pyranylidene 6 a in 43 % yield together with a significant proportion of the a-oxoketene dimer [Scheme 4, Eq. (a)]. Because two molecules of ylides were clearly incorporated in the product 6 a, the same reaction was attempted with two equivalents of the ylide, which afforded this time the 4H-pyranylidene 6 a in 89 % yield. This pseudo three-component reaction could be generalized, allowing for the expeditious synthesis of 4H-pyranylidenes 6 a-f [Scheme 4, Eq. (b)]. In the case of product 6 f, a minor amount of the diastereomer iso-6 f could also be isolated in 7 % yield. The structures of 6 e and 6 f were secured by X-ray diffraction analyses. Notably, 4H-pyranylidenes of type 6 are donor-acceptors pconjugated molecules with potential applications as nonlinear optical chromophores. [9] The 4H-pyranylidenes 6 a-e, having a 2-methoxyl substituent, are relatively stable compounds showing no significant decomposition when stored neat in closed reaction vessels at ˇ18 8C for several months. However, 4H-pyranylidene 6 c could be cleanly converted into the corresponding 2H-pyran-2-one 7 c upon prolonged exposure to air at room temperature [Scheme 4, Eq. ( c)]. Similarly, 4H-pyranylidene 6 e could be rapidly converted into 2H-pyran-2-one 7 e in the presence of aqueous HCl [Scheme 4, Eq. ( c)]. These internal redox transformations are supposedly promoted by water. By extension, the synthetic approach to 4H-pyranylidenes 6 a-e depicted in Scheme 4 also constitutes a practical method to prepare the corresponding substituted 2H-pyran-2-ones, which is another important class of synthetically and biologically relevant molecules. [10] To identify a plausible reaction pathway accounting for the formation of 4H-pyranylidenes 6 a-f, two control experiments were performed. First, a 1:1 mixture of 4H-pyran-4-one 5 e and Wittig ylide 2 e in toluene was heated at 170 8C for 15 min [Scheme 5, Eq. (a)]. Both starting materials were nearly quantitatively recovered, and no formation of the 4H-pyranylidenes 6 f or iso-6 f could be evidenced, ruling out the possibility for a Wittig reaction between the ketone carbonyl group in 4Hpyran-4-one 5 e and phosphorous ylide 2 e. [START_REF] Minami | For examples of Wittig-type olefinations of 4H-pyran-4-one derivatives[END_REF] Second, a 1:1 mixture of allene Based on the above experimental data, it was enticing to postulate some empirical rules governing the fate of the reactions of carbonyl-stabilized phosphorous ylides with a-oxoketenes: 1) a,a'-bisoxoallenes of type 4 may be obtained by standard Wittig olefinations of acyclic-only a-oxoketenes; 2) ketone-stabilized Wittig ylides generally react with a-oxoketenes to give g-pyrones of type 5 through abnormal Wittig olefinations; 3) ester-stabilized ylides react with a-oxoketenes by a pseudo three-component Wittig/abnormal Wittig cascade olefination to afford 4H-pyranylidenes of type 6 via the corresponding a,a'-bisoxoallene intermediates 4; and 4) the phenyl ketone-stabilized ylide 2 e is a border case. However, the actual reasons dictating the divergent reactivities observed in these series warranted further research. With the intention to elucidate the mechanism of the abnormal Wittig olefination and to identify the origin of the dichotomy in the reactions of carbonyl-stabilized Wittig ylides 2 with a-oxoketenes 3, we embarked on a detailed mechanistic computational study using DFT methods. This part of the study revealed several unusual features for Wittig olefinations. As a short background on the classical Wittig olefination, it is now generally accepted that the lithium salt-free Wittig olefination of a carbonyl compound with a carbonyl-stabilized phosphorous ylide is a three-step process initiated by an irreversible regio-and stereoselective [2+ +2] cycloaddition between the C=O bond of the carbonyl compound and the C=P bond of the ylide, leading to an oxaphosphetane intermediate. [12] Given that bond-forming and -breaking events at pentavalent bipyramidal phosphorus atoms preferentially occur from apical positions, the oxaphosphetane intermediate then requires a low-energy-demanding geometrical reorganization at the phosphorus atom, the socalled Berry pseudorotations, [13] before its decomposition by a retro-[2+ +2] cycloaddition affording the olefin product and triphenylphosphine oxide. To get a realistic model for the Wittig olefinations described herein, calculations were performed at the B3LYP/6-311 + +G(d,p)//B3LYP/6-31 + G(d) level of theory including a continuum description of solvation effects, and, importantly, with the full PPh 3 ylides to account for all the steric and electronic effects. [START_REF]See Supporting Information for details. It may be noted that the present study is the first realistic computational mechanistic study[END_REF] Both the normal and abnormal Wittig olefinations of the a-oxoketene 3 d having a blocked s-cis conformation were comparatively examined with the ketone-stabilized ylide 2 d and the ester-stabilized ylide 2 c (Figures 12345). Importantly, all reactions were found to be initiated by the formation of a covalent bond between the nucleophilic ylidic carbon atom and the electrophilic ketene carbon atom to produce, respectively, the stabilized betaine intermediates I and V with a reasonable barrier (Figure 1). All efforts directed at the identification of alternative processes excluding the intermediary of the betaines I or V remained fruitless. Significantly, betaine intermediates were previously demonstrated not to form in the course of standard Lewis acid-free Wittig olefinations, [12] and on that matter the reactions described herein are peculiar. The strain release resulting from the sp to sp 2 rehybridization at the addition carbon atom together with the formation of pextended zwitterionic ketoenolates leading to six-membered chelates by hydrogen bonding certainly contribute to the stabilization of betaines I and V.

For the synthesis of the g-pyrone 5 a (Figure 2), betaine I adopts the geometry I bis suitable for the formation of the tricyclic oxaphosphetane intermediate II by a hemiacetalization/oxaphosphetane formation cascade. In oxaphosphetane II, the oxygen atom of the former acetyl stabilizing group of the ylide is in an apical position (with a 11.88 deviation from alignment) at the phosphorus atom that adopts a trigonal bipyramid ge-ometry. A geometrical reorganization at the pentavalent phosphorous atom (Berry pseudorotation) is then necessary to obtain the oxaphosphetane intermediate II bis , having this time the former ylidic carbon atom in an apical position (with a 21.58 deviation from alignment). This conformational change For the concurrent synthesis of the a,a'-bisoxoallene 4 h from the same substrates, which is not observed experimentally, it was found that the betaine intermediate I can cyclize to the oxaphosphetane intermediate III, having the former ylidic carbon atom in an apical position (Figure 3). The expected oxaphosphetane intermediate, having the oxygen atom of the former ketene carbonyl group in an apical position, is actually formed as a shoulder on the raising energy profile from I, and requires no significant activation energy (see the Supporting Information for details). Very surprisingly, and in sharp contrast to the well-established oxaphosphetane decomposition process by asynchronous retro-[2+ +2] cycloaddition (e.g. II bis !5 a in Figure 2), the only reaction path we could identify for the decomposition of III is a two-step process. Indeed, oxaphosphetane III was found to evolve by rupture of the CˇP bond and some conformational change to afford the unusual betaine intermediate IV. [START_REF] Clennan | Related dioxatriphenylphosphoranes have been isolated in the past[END_REF] Intermediate IV, which shows both a covalent OˇP bond (d O-P = 1.66 ä) and an electrostatic O ˇ/P + stabilizing interaction (d O-P = 1.91 ä), may be regarded as a Lewis pair adduct between triphenylphosphine oxide and the a,a'-bisoxoallene 4 h (with d C-O = 1.40 ä) stabilized by an electron retro-donation from the negatively charged oxygen atom of the acetyl group in the apical position (with a 4.68 deviation from alignment) to the electron-demanding phosphorus atom. The separation of this Lewis pair can occur with a small barrier (+ 37.8 kJ mol ˇ1) to afford the a,a'-bisoxoallene 4 h and triphenylphosphine oxide.

Overall, these calculations indicate that the g-pyrone abnormal Wittig product 5 a is the thermodynamic product by 91.1 kJ mol ˇ1, and that the allene regular Wittig product 4 h is the kinetic product by only 14.6 kJ mol ˇ1. [START_REF]From this model study, the calculated half-life of 4 h was estimated at t 1/2 = 2.5 h (with the pre-exponential factor of the Eyring equation assumed to be 1), which appears over-estimated. Also, an overall barrier of 159.7 kJ mol ˇ1 would be involved in the reaction 4 h!5 a, which also appears over-estimated. Given the large approximations of the model employed, relative errors of up to ⌃ 40 kJ mol ˇ1 are undoubtedly[END_REF] To experimentally demonstrate possible reversibility in the abnormal Wittig olefination leading to the g-pyrone 5 l (Scheme 1), a deuterated benzene solution of allene 4 a was heated 30 minutes at 200 8C in the presence of triphenylphosphine oxide with an internal standard (Scheme 6). The 1 H NMR analysis of the resulting mixture revealed the formation of 8 % of the expected g-pyrone 5 l together with the presence of 67 % unreacted 4 a and some unidentified products. A similar reaction performed without triphenylphosphine oxide showed no significant reaction of 4 a. Although poorly efficient, the rearrangement of 4 a into 5 l in the presence of triphenylphosphine oxide, presumably involving the betaine I', points out the existence of a kind of retro-Wittig process with a C=O bond being created from a C=C bond and triphenylphosphine oxide.

We next examined computationally the reactions of the model a-oxoketene 3 d with the ester-stabilized Wittig ylide 2 c. Paralleling the findings shown in Figure 2, betaine V was found to evolve to the g-pyrone product 5 n by a cascade double cyclization, affording consecutively the two oxaphosphetane intermediates VI and VI bis , the decomposition of which by a retro-[2+ +2] cycloaddition gives the product (Figure 4). Overall, the energy profiles depicted in Figure 2 and Figure 4 are, as expected, very comparable; however, with a significant difference: the rate limiting step lies + 119.1 kJ mol ˇ1 above the energy of betaine I in Figure 2 whereas it is now calculated at + 153.1 kJ mol ˇ1 above the energy of betaine V in Figure 4. In other words, in the ketonestabilized Wittig ylide series, the conversion of betaine I into gpyrone 5 a can proceed at a rapid rate under the reaction conditions, whereas under similar conditions in the ester-stabilized Wittig ylide series the betaine V can only very slowly convert into g-pyrone 5 n. This difference in reactivity actually reflects the lower reactivity of ester versus ketone carbonyl groups in anionic cascade processes. [START_REF] Bugaut | [END_REF] Finally, we examined the concurrent pathway leading to a,a'-bisoxoallene 4 i from betaine V (Figure 5). In this case, it was found that betaine V can readily undergo the C!O 1,3-shift of the triphenylphosphonium group to give intermediate VII directly via a near planar oxaphosphetane transition state. The latter actually corresponds to the rupture of the CˇP bond in an elusive oxaphosphetane intermediate having the former ylidic carbon atom in an apical position at phosphorous (i.e., the analogue of III with a methyl ester group in place of the acetyl group, see the Supporting Information for details). As before, intermediate VII may be regarded as a Lewis pair adduct between triphenylphosphine oxide and the a,a'-bisoxoallene 4 i stabilized by an electron retro-donation from the negatively charged oxygen atom of the carbonyl in the methyl ester group in the apical position (with a 6.38 deviation from alignment) to the electron demanding phosphorous atom. However, this electrostatic O ˇ/P + interaction is much weaker than above (d O-P = 3.00 ä), resulting in a less stabilized Lewis pair (compare the relative stabilities of IV and VII). This is easily rationalized by the preferred delocalization of the negative charge in VII on the distal ketone carbonyl oxygen atom rather than the methyl ester one. As above, the separation of the Lewis pair VII occurs with a small barrier (+ 29.4 kJ mol ˇ1) to afford a,a'-bisoxoallene product 4 i together with triphenylphosphine oxide. The ratelimiting step of the overall transformation is the 1,3shift of the triphenyphosphonium group, with an activation energy of + 101.5 kJ mol ˇ1 relative to the energy of the betaine V. From this series of calculations, it was concluded that the preferential formation of a,a'-bisoxoallene 4 i over g-pyrone 5 n in the reaction between a-oxoketene 2 a and methyl esterstabilized Wittig ylide 3 h is under sharp kinetic control, with the formation of the allene being ca. 10 6 times faster than the formation of the pyrone.

The above model study shows that ester-stabilized Wittig ylides react with a-oxoketenes to afford preferentially the corresponding a,a'-bisoxoallenes 4 As shown in the example in Equation (a), Scheme 4, the a,a'-bisoxoallene 4 g, having a blocked s-cis conformation of the a-oxoallene moiety, reacts faster with the ester-stabilized ylide 2 c than the s-cis a-oxoketene derived from the diazo 1 e, precluding the isolation of a,a'-bisoxoallene 4 g. However, this situation is reverted in the case of the a,a'-bisoxoallenes 4 b,c,e, capable of adopting a s-trans conformation of the aoxoallene moieties (Scheme 1). As demonstrated by the model study, the abnormal Wittig olefination can only be operative with a,b-unsaturated carbonyl compounds having an s-cis conformation. In the cases of a,a'-bisoxoallenes 4 b,c,e, the favored s-trans conformations of their a-oxoallene moieties are unproductive, slowing down their participation in abnormal Wittig processes and allowing their isolation under some conditions. Similarly, the a-oxoketenes derived from the acyclic diazo compounds 1 a,c predominantly exist in their s-trans conformations, which here again slows down their abnormal Wittig reactivity to the benefit of the normal Wittig reactivity, allowing for the isolation of a,a'-bisoxoallenes 4 a,d,f (Scheme 1).

Conclusions

The reactions of a-oxoketenes, prepared in situ by a thermal Wolff rearrangement of 2-diazo-1,3-dicarbonyl compounds, with carbonyl-stabilized Wittig ylides have been studied in detail. It was found that a-oxoketenes generally react with ketone-and aldehyde-stabilized Wittig ylides as 1,4-ambident C-electrophilic/O-nucleophilic reaction partners via an abnormal Wittig olefination, unlocking the synthesis of 4H-pyran-4one (g-pyrone) derivatives with original substitution patterns. This reaction presumably involves some degree of thermodynamic control when compared to the normal Wittig olefination of the a-oxoketenes, and some reversibility in the normal Wittig olefination was demonstrated: a premiere! In sharp contrast, ester-stabilized Wittig ylides were found to react with aoxoketenes through a normal Wittig olefination, affording a,a'bisoxoallenes. This reaction was shown to be under kinetic control when compared to the corresponding abnormal Wittig olefination. The actual reasons at the origin of the divergent reactivities observed for ketone-stabilized ylides on the one hand and ester-stabilized ylides on the other hand were investigated, notably through a comprehensive computational mechanistic study, and were ultimately found to reside in the higher electrophilicity of ketone carbonyl groups versus ester ones. In most cases, the a,a'-bisoxoallene products were found to be reactive under the reaction conditions and capable, in turn, of undergoing an abnormal Wittig olefination with a second equivalent of Wittig ylide, leading to 4H-pyranylidenes by a pseudo three-component reaction involving a Wolff/ Wittig/abnormal Wittig cascade sequence. Until now, the abnormal Wittig olefination was a laboratory oddity and the present work is the first report on its generalization, rationalization, and concrete synthetic applications. Overall, the chemical transformations described herein, involving the two venerable and thoroughly explored Wolff rearrangement and Wittig olefination, carry a significant improvement to the current knowhow for the selective synthesis of functionalized 4H-pyran, and, to some extent, 2H-pyran derivatives. In a broader meaning, the abnormal Wittig olefination of a,b-unsaturated carbonyl compounds with carbonyl-stabilized Wittig ylides can now be added to the arsenal of synthetic methods to prepare 4Hpyran derivatives. From a fundamental point of view, and contrary to the standard Lewis acid-free Wittig olefination of carbonyl compounds with carbonyl-stabilized phosphorous ylides, the Wittig and abnormal Wittig reactions described herein are likely to proceed via betaine intermediates.

Experimental Section

General procedure for the synthesis of a,a'-bisoxoallenes 4 a-f, 4H-pyran-4-ones 5 a-l, and 4H-pyranylidenes 6 a-f: A 10 mL seal- able oven-dried tubular reaction vessel was charged with diazo compound 1 (ca. 0.2-1.0 mmol), phosphorous ylide 2 (1.0 or 2.0 equiv), and dry toluene (2 mL). The resulting heterogeneous mixture was subjected to microwave irradiation to reach 170 8C as fast as possible and held at that temperature for 15 minutes, after which the reaction mixture was cooled to 55 8C with an air flow. The resulting solution was concentrated under vacuum and directly purified by silica gel flash chromatography to afford the pure product. CCDC 1550800(5 a), 1550801 (6 e) and 1550802 (6 f) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre.

  4 e and Wittig ylide 2 c in toluene was heated at 170 8C for 15 minutes [Scheme 5, Eq. (b)]. Pleasingly, the analysis of the product reaction mixture evidenced the clean and efficient formation of 4H-pyranylidene 6 e, pointing to allene 4 e as a key intermediate capable of undergoing an abnormal Wittig olefination step in the cascade transformation 1 a + 2 c!6 e.

Figure 1 .

 1 Figure 1. Reactions of a-oxoketene 2 a with acetyl-stabilized Wittig ylide 3 a and methyl ester-stabilized ylide 3 h to produce betaines I and V, respectively. All energies are Gibbs free energies expressed in kJ mol ˇ1.

Figure 2 .

 2 Figure 2. Energy profile of the reaction leading to g-pyrone 5 a. All energies are Gibbs free energies expressed in kJ mol ˇ1.Chem.Eur. J. 2018, 24, 11110 -11118

Figure 3 .

 3 Figure 3. Energy profile of the reaction leading to allene 4 h (not observed experimentally). All energies are Gibbs free energies expressed in kJ mol ˇ1.

Figure 4 .

 4 Figure 4. Energy profile of the reaction leading to g-pyrone 5 n. All energies are Gibbs free energies expressed in kJ mol ˇ1.

Figure 5 .

 5 Figure 5. Energy profile of the reaction leading to allene 4 i. All energies are Gibbs free energies expressed in kJ mol ˇ1.

Scheme 7 .

 7 Scheme 7. Mechanistic hypothesis for the formation of 4H-pyranylidenes 6 via a Wittig/abnormal Wittig cascade reaction.

Scheme 1. Synthesis of a,a'-bisoxoallenes 4 by normal Wittig olefination of a-oxoketenes 3. Scheme 3. Carbonyl-stabilized Wittig ylides as synthetic equivalents of alkynes. Scheme 2. Synthesis of g-pyrones 5 by abnormal Wittig olefination of a-oxoketenes 3. [a] The reaction also afforded the products 6 f (22 %) and iso-6 f (4 %), see text and Scheme 4. [b] Obtained from 2,2,6-trimethyl-4H-1,3dioxin-4-one (1 h) instead of 2-diazo-3-oxobutanal. Chem. Eur. J. 2018, 24, 11110 -11118 www.chemeurj.org ⌫ 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Scheme 4. Synthesis of 4H-pyranylidenes 6 by a Wittig/abnormal Wittig cascade olefination of a-oxoketenes. Scheme 5. Control experiments. Chem. Eur. J. 2018, 24, 11110 -11118 www.chemeurj.org ⌫ 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org ⌫ 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem.Eur. J. 2018, 24, 11110 -11118 www.chemeurj.org⌫ 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Acknowledgements

We thank Dr. Michel Giorgi (CNRS) for the X-ray structural analyses, Dr. Michel Rajzmann (Aix-Marseille Universitÿ) for assistance in computational chemistry, and the Centre Rÿgional de Compÿtences en Modÿlisation Molÿculaire (Aix-Marseille Universitÿ) for computing facilities. Financial support from the Agence Nationale de la Recherche (ANR-13-JS07-0002-01), Aix-Marseille Universitÿ and the Centre National de la Recherche Scientifique (CNRS) is gratefully acknowledged.

Conflict of interest

The authors declare no conflict of interest.