Regioselective microwave-assisted synthesis of substituted pyrazoles from ethynyl ketones

Reaction of alpha,beta-ethynyl ketones and hydrazine derivatives gives 1,3- and 1, 5 -disubstituted pyrazoles in good yield. Microwave irradiation in concentrated hydrochloric acid-methanol (1.5% v/v), with concurrent cooling at sub-ambient temperatures or at 120 degrees C, for 30 or 2 minutes, respectively, facilitates rapid heterocyclization and preferentially gives the 1,3 -disubstituted regioisomer.