Sequential Visible-Light and <i>N</i>-Heterocyclic Carbene Catalysis: Stereoselective Synthesis of Tetrahydropyrano[2,3-<i>b</i>]indoles

Abstract

An efficiently stereoselective [4 + 2] cycloaddition of 3-alkylenyloxindoles and α-diazoketones through sequential visible-light photoactivation and <i>N</i>-heterocyclic carbene catalysis was achieved. A series of tetrahydropyrano[2,3-<i>b</i>]indoles with an all-carbon quaternary stereocenter were obtained in good yields with excellent diastereo- and enantioselectivities.