Chiral nickel(Ⅱ)complex catalyzed asymmetric(3+2)cycloaddition ofα-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 de-sired dihydrofuran O,O-acetal derivatives were obtained in good yields(up to 90％)with high enantios-electivity(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.