6,6-Dicyanopentafulvenes: Electronic Structure and Regioselectivity in [2+2] Cycloaddition-Retroelectrocyclization Reactions

作者：Finke Aaron D; Dumele Oliver; Zalibera Michal; Confortin Daria; Cias Pawel; Jayamurugan Govindasamy; Gisselbrecht Jean Paul; Boudon Corinne; Schweizer W Bernd; Gescheidt Georg; Diederich Francois^*

来源：Journal of the American Chemical Society, 2012, 134(43): 18139-18146.

DOI：10.1021/ja309141r

We present an investigation of the electronic properties and reactivity behavior of electron-accepting 6,6-dicyanopentafulvenes (DCFs). The electron paramagnetic resonance (EPR) spectra of the radical anion of a tetrakis(silylalkynyl) DCF, generated by Na metal reduction, show delocalization of both the charge and unpaired electron to the nitrogens of the cyano moieties and also, notably, to the silicon atoms of the four alkynyl moieties. By contrast, in the radical anion of the previously reported tetraphenyl DCF, coupling to the four phenyl rings is strongly attenuated. The data provide physical evidence for the different conjugation between the DCF core and the substituents in both systems. We also report the preparation of new fulvene-based push-pull chromophores via formal [2 + 2] cycloaddition-retroelectrocyclization reaction of DCFs with electron-rich alkynes. Alkynylated and phenylated DCFs show opposite regioselectivity of the cycloaddition, which can be explained by the differences in electronic communication between substituents and the DCF core as revealed in the EPR spectra of the radical anions.

• 出版日期2012-10-31