Asymmetric Aerobic Oxidative Cross-Coupling of Tetrahydroisoquinolines with Alkynes

An efficient asymmetric aerobic oxidation of tetrahydroisoquinolines with terminal alkynes was realized under mild reaction conditions using O-2 as the sole oxidant. A chiral N,N'-dioxide/zinc(II)/iron(II) bimetallic cooperative catalytic system proves to be efficient for the formation of various alpha-alkynyl substituted tetrahydroisoquinolines in good to excellent yields and enantioselectivities. A primary mechanistic study supports an enantioselective electrophilic addition of zinc acetylide to the iminium intermediates, formed through a molecular O-2-involved oxidative process.