Tropylium Salt-Promoted Vinylogous Aza-Michael Addition of Carbamates to para-Quinone Methides: Elaboration to Diastereomerically Pure α,α′-Diarylmethyl Carbamates

Abstract

Carbocation catalysis is emerging as an important subarea of Lewis acid catalysis. Some stable and isolable carbocations have been successfully utilized as Lewis acid catalysts and promoters in many synthetic transformations. In this manuscript, we report a tropylium cation-promoted vinylogous aza-Michael addition of carbamates to para-quinone methides (QMs) to access a wide range of unsymmetrical α,α′-diarylmethyl carbamates. This mild protocol was effective for the vinylogous conjugate addition of (−)-menthyl carbamate to p-QMs, and the respective diastereomerically pure α,α′-diarylmethyl carbamate derivatives could be obtained in excellent yields and diastereoselectivities (up to >20:1 de).