Synthesis of 1,3,4-Trisubstituted Pyrazoles from α-(1,3-Dithian2-yl) Enamine Ketones via [4+1] Cyclization

A novel method for the synthesis of 1,3,4-trisubstituted pyrazoles from alpha-(1,3-dithian-2-yl) enamine ketones and primary amines, involving copper(II)-catalyzed oxidative N-N coupling, has been developed. This unprecedented [4+1] approach is versatile in the synthesis of N-aryl, N-benzyl and N-alkyl pyrazoles, and provides an alternative to the conventional [3+2] methods.