Lewis-Base-Catalyzed Asymmetric [3 + 3] Annulation Reaction of Morita–Baylis–Hillman Carbonates: Enantioselective Synthesis of Spirocyclohexenes

A Lewis-base-catalyzed enantioselective [3 + 3] annulation reaction of Morita–Baylis–Hillman (MBH) carbonates with α-arylidene pyrazolinones is described, affording the pyrazolone-fused spirocyclohexenes bearing an all-carbon quaternary stereocenter in high yields with good to excellent diastereoselectivities and excellent enantioselectivities.