Copper-catalyzed propargylic [3+3] cycloaddition with 1H-pyrazol-5(4H)-ones: enantioselective access to optically active dihydropyrano[2,3-c]pyrazoles.

A copper-catalyzed asymmetric propargylic [3+3] cycloaddition with 1H-pyrazol-5(4H)-ones as C,O-bisnucleophiles through the desilylation-activated strategy has been developed. With the catalysis of Cu(OAc)2·H2O in combination with a chiral tridentate P,N,N-ligand, the reaction displayed a broad substrate scope, and thus provided a variety of chiral dihydropyrano[2,3-c]pyrazoles in high yields and with excellent enantioselectivities (up to 96% ee).