Cyclopropane derivatives photoinduced electron

Arylcyclopropanes and their heterocyclic analogues are liable to electron transfer induced fragmentation of a carbon-carbon bond that in some cases leads to synthetically useful products. Thus, 1,2-diarylcyclopropanes [240-243] as well as 2,3-diaryloxirans [244-246] and -aziridines (in the last case, also 2-monophenyl derivatives) [247,248] are cleaved upon photoinduced electron transfer sensitization. The final result, after back electron transfer, is trans-cis isomerization of the ring. In the presence of a suitable trap, however, a cycloaddition reaction takes place, involving either the radical cation or the ylide. Thus, dioxoles, ozonides or azodioxoles, respectively, are formed in the presence of oxygen and oxazolidines have been obtained from cyclopropanes in the presence of nitrogen oxide (Sch. 23). 

PHOTOINDUCED ELECTRON TRANSFER REACTIONS OF CYCLOPROPANE DERIVATIVES Tsutomu Miyashi, Hiroshi Ikeda,... 

Mizuno, K. and Otsuji, Y, Addition and cycloaddition reactions via photoinduced electron transfer, in Topics in Current Chemistry, Vol. 169, Mattay, J., Ed., Springer-Verlag, Berlin, 1994, p. 301. Miyashi, X, Ikeda, H., Takahashi, Y, and Akiyama, K., Photoinduced electron transfer reactions of cyclopropane derivatives, in Advances in Electron Transfer Chemistry, Vol. 6, Mariano, P.S., Ed., Jai Press Inc., Stamford, CT, 1999, p. 1. 

A survey of the literature reveals some characteristic photochemical features of homoquinones (1) [2+2]-photocycloaddition with alkenes and alkynes, (2) hydrogen abstraction and/or ring opening of incorporated cyclopropane, and (3) photoinduced electron transfer reactions, as described below. The photocycloaddition with alkenes and alkynes took place exclusively at the ethylene linkage of homobenzoquinones to afford cyclobutanes (or cyclobutene derivatives) regio- and exo/endo stereoselectively, depending on the identity of both the homobenzoquinones as well as the alkenes. 

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