Stereoselective synthesis of pyrano[2,3-c]pyrazolone derivatives via light-induced NHC catalyzed [4 + 2] annulations

Abstract

Herein, chiral pyrano[2,3-c]pyrazolone derivatives bearing vicinal tertiary and quaternary carbon stereocenters have been synthesized via light-induced N-heterocyclic carbene (NHC) catalyzed asymmetric [4 + 2] cycloaddition of 4-arylidenylpyrazolones and α-diazoketones in moderate to good yields with good enantio- and diastereoselectivities (24 examples, up to 93% yield, 95% ee and >20 : 1 dr). This protocol features mild reaction conditions, high efficiency, and broad substrate scope.