Regiodivergent Synthesis of 3,4- and 4,5-Disubstituted N -Methylpyrazoles from 4-Acyl-1 H -pyrrole-2,3-dione and Methylhydrazine.

A simple, efficient and highly regioselective method for the preparation of 3,4- and 4,5-disubstituted N -methylpyrazoles in a one-pot procedure is reported. The methodology developed was based on the regiochemical control of the reaction of 4-acyl-1 H -pyrrole-2,3-diones and methylhydrazine with an influence of the addition or absence of acid and the substrate structure.