Harnessing Vinylogy with Radicals: Photoinduced γ-Benzylation Reactions of 2-Silyloxyfurans

2-Silyloxyfurans are among the most exploited Mukaiyama-type vinylogous nucleophiles from which a myriad of bioactive gamma-butyrolactones have been accessed. Although a plethora of "polar" reactions featuring this scaffold as a key player have been developed so far, its behavior in radical chemistry is still in its infancy. Herein, the development of two complementary vinylogous, radical-mediated benzylations of 2-silyloxyfurans, promoted by visible light and suitable photoredox catalysts, is described. Common to both photocatalytic cycles is the reduction of a suitable redox active ester forging a key benzyl radical intermediate, which undergoes two different fates. First, the photoinduced oxidation of the silyloxyfuran generates an unprecedented silyl-radical cation species able to trap the nucleophilic benzyl radical. Alternatively, with specific electron-rich substrates, the benzyl radical can be converted to the corresponding benzyl carbocation intermediate via a net-neutral radical-polar crossover pathway, enabling a vinylogous, polar benzylation reaction. A broad scope of chiral, gamma-benzyl butenolides is obtained in one step, some of which are used as strategic precursors to access bioactive phenyl-gamma-valerolactone metabolites.