Leveraging the persistent radical effect in the synthesis of trans-2,3-diaryl-dihydrobenzofurans


A simple method for accessing trans-2,3-diaryl-dihydrobenzofurans is reported. This approach leverages a persistent radical equilibrium between quinone methide dimers and the persistent phenoxyl radicals derived therefrom. This equilibrium is disrupted by phenols that yield transient phenoxyl radicals, leading to cross-coupling between persistent and transient radicals. The resultant quinone methides with pendant phenols rapidly cyclize to dihydrobenzofurans (DHBs). This putatively biomimetic access to dihydrobenzofurans provides superb functional group tolerance and a unified approach for the synthesis of resveratrol-based natural products.