The Diels–Alder Reaction of 4,6‐Dinitrobenzofuroxan with 1‐Trimethylsilyloxybuta‐1,3‐diene: A Case Example of a Stepwise Cycloaddition |
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Authors: | Sami Lakhdar Dr François Terrier Prof Dominique Vichard Guillaume Berionni Nizar El Guesmi Régis Goumont Prof Taoufik Boubaker Prof |
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Institution: | 1. Institut Lavoisier de Versailles, UMR 8180, Université de Versailles, 45 Avenue des Etats‐Unis, 78035 Versailles Cedex (France), Fax: (+33)?139254452;2. Unité de Recherche de Physico‐Chimie Moléculaire, Faculté des Sciences de Monastir, Avenue de l'Environnement, 5019 Monastir (Tunisia) |
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Abstract: | The reaction of 4,6‐dinitrobenzofuroxan (DNBF) with 1‐trimethylsilyloxybuta‐1,3‐diene ( 8 ) is shown to afford a mixture of 2+4] diastereomeric cycloadducts ( 10 , 11 ) through stepwise addition–cyclization pathways. Zwitterionic intermediate σ‐adduct 9 , which is involved in the processes, has been successfully characterized by 1H and 13C NMR spectroscopy and UV/visible spectrophotometry in acetonitrile. A kinetic study has been carried out in this solvent that revealed that the rate of formation of 9 nicely fits the three‐parameter equation log k=s(E+N) developed by Mayr to describe the feasibility of nucleophile–electrophile combinations. This significantly adds to the NMR spectroscopic evidence that the overall cycloadditions take place through a stepwise mechanism. The reaction has also been studied in dichloromethane and toluene. In these less polar solvents, the stability of 9 is not sufficient to allow direct characterization by spectroscopic methods, but a kinetic investigation supports the view that stepwise processes are still operating. An informative comparison of our reaction with previous interactions firmly identified as prototype stepwise cycloadditions is made on the basis of the global electrophilicity index, ω, defined by Parr within the density functional theory, and highlighted by Domingo et al. as a powerful tool for understanding Diels–Alder reactions. |
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Keywords: | cycloaddition density functional calculations Diels– Alder reactions nitrobenzofuroxans superelectrophilic heteroaromatics |
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