Solvent‐ and Transition Metal Catalyst‐Dependent Regioselectivity in the [3+2] Cyclocondensation of Trifluoromethyl<i>‐</i>α,β<i>‐</i>ynones with Hydrazines: Switchable Access to 3‐ and 5‐Trifluoromethylpyrazoles

Abstract

Abstract The regioselectivity of the [3+2] cyclocondensation of trifluoromethyl ‐ α,β ‐ ynones with hydrazines can be readily tuned to preferentially afford either 3‐ or 5‐trifluoromethylpyrazoles through variation of the reaction conditions. Under catalysis with copper(II) acetate (2.0 mol%), cyclocondensation proceeded smoothly to yield 3‐trifluoromethylpyrazoles with high regioselectivity. In contrast, when the reaction was conducted in dimethyl sulfoxide under catalyst‐free conditions, the formation of 5‐trifluoromethylpyrazoles was predominantly observed. magnified image