Organocatalytic Enantioselective Synthesis of Pyrazoles Bearing a Quaternary Stereocenter

Abstract

An efficient one-pot asymmetric synthesis of pyrazoles bearing a chiral quaternary stereocenter has been developed. Quinine-derived thiourea catalyzed the enantioselective addition of pyrazolones to isatin-derived ketimines, providing the corresponding acetylated pyrazoles after in situ treatment with Ac2O/Et3N. The corresponding pyrazoles were afforded in high yields and excellent enantioselectivities. Four's a charm: In an efficient one-pot asymmetric synthesis, pyrazoles bearing a chiral quaternary stereocenter are synthesized by enantioselective addition of pyrazolones to isatin-derived ketimines. The reaction is catalyzed by quinine-derived thiourea, and the corresponding acetylated pyrazoles are obtained in high yields and excellent enantioselectivities after in situ treatment with Ac2O/Et3N.