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

Le résumé fourni par la source

2‐Silyloxyfurans are among the most exploited Mukaiyama‐type vinylogous nucleophiles from which a myriad of bioactive γ‐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, γ‐benzyl butenolides is obtained in one step, some of which are used as strategic precursors to access bioactive phenyl‐γ‐valerolactone metabolites.

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