Facile ring opening of siloxy cyclopropanes by photoinduced electron transfer. A new way to β-keto radicals

Abstract

Siloxy cyclopropanes undergo ring opening and fragmentation of formal silyl cations under formation of β-keto radicals. These reactive intermediates can be used in inter- and intramolecular addition reactions leading to complex ring systems if more than one unsaturated side chain is present in the starting material. Beside some synthetic examples mainly the mechanism will be discussed focusing on the structure of the primarily formed radical cations, the regioselectivity of cyclopropane cleavage (endo vs exo ring opening), leaving of the silyl group, and termination by H-transfer.