Catalytic asymmetric dearomative [4 + 2] annulation of 2-nitrobenzofurans and 5H-thiazol-4-ones: stereoselective construction of dihydrobenzofuran-bridged polycyclic skeletons

Abstract

An organocatalytic asymmetric dearomative [4 + 2] annulation of 2-nitrobenzofurans and 5H-thiazol-4-ones is described for the first time. With a chiral dipeptide-based squaramide as the catalyst, a series of dihydrobenzofuran-bridged polycyclic compounds bearing four contiguous stereocenters including three quaternary stereogenic centers were obtained with excellent diastereoselectivities and high enantioselectivities under mild conditions. Preliminary biological evaluation indicated that the products exhibit impressive cytotoxicity against the human cancer cell lines A549 and K562.