Chiral nickel(II) complex catalyzed asymmetric (3 + 2) cycloaddition of α‐diazo pyrazoleamides with 2‐siloxy‐1‐alkenes

A highly efficient asymmetric (3 + 2) cycloaddition of α-diazo pyrazoleamides with silyl enol ethers was realized by employing a chiral N,N'-dioxide-Ni(II) complex catalyst. The process includes the formation of chiral nickel carbenoid intermediate and the following enantioselective cycloaddition reaction. The desired dihydrofuran O,O-acetal derivatives were obtained in good yields (up to 90%) with high enantioselectivity (up to 99% ee) under mild reaction conditions within short reaction time. On the basis of the determination of the catalyst structure, a possible transition state mode was proposed.