Recent Advances on the Construction of Chiral Dihydrobenzofurans by Asymmetric [3+2] Cyclization Reactions of Phenols (Quinones) and Alkenes

Dihydrobenzofuran structural units are widely present in bioactive natural products, and therefore, this type of natural products have attracted extensive attention from synthetic organic chemists and pharmaceutical chemists. In recent years, enantioselective formation of this structural unit, especially its C2 and C3 vicinal chiral stereocenters, has always been one of challenging problems in the field of synthetic methodology. Among some methods, the construction of optically active dihydrobenzofuran structural units from [3+2] cyclizations of phenols (quinones) and olefins via asymmetric catalysis or induction by chiral auxiliaries developed rapidly. In this review, we summarized the recent progress of asymmetric [3+2] cyclization reactions with different types of chiral catalysts and auxiliaries, especially with emphasis on understanding the control of stereoselectivies in these methods. Meanwhile, the application in the total synthesis of dihydrobenzofurans enabled by asymmetric [3+2] cyclization reactions was briefly introduced. Finally, the future development trend of asymmetric [3+2] cyclization reactions was analyzed, in order to stimulate the emergence of highly efficient and general catalytic system.