Enantioselective synthesis of functionalized pyrazoles by NHC-catalyzed reaction of pyrazolones with α,β-unsaturated aldehydes

Org Lett. 2015 Mar 20;17(6):1417-20. doi: 10.1021/acs.orglett.5b00293. Epub 2015 Feb 27.

Abstract

The N-heterocyclic carbene (NHC)-organocatalyzed enantioselective annulation reaction of pyrazolones with α,β-unsaturated aldehydes proceeding via the chiral α,β-unsaturated acyl azolium intermediates under oxidative conditions is presented. The reaction afforded dihydropyranone-fused pyrazoles in moderate to good yields and good er values under operationally simple and base-free conditions.