Regiocontrolled Synthesis of 1-Substituted-3(5)-carboxyalkyl-1 H -pyrazoles Using Trichloromethyl Enones.

In this work, we present a regiocontrolled methodology to prepare 1-substituted-3(5)-carboxyalkyl-1 H -pyrazoles using trichloromethyl enones as starting materials. It was found that the selectivity of the reaction depends on the nature of the hydrazine: when using arylhydrazine hydrochlorides, synthesis of the 1,3-regioisomer was achieved (22 examples, 37-97% yields), while the corresponding free hydrazine led exclusively to the 1,5-regioisomer (12 examples, 52-83% yields). The trichloromethyl group was used as a precursor for the carboxyalkyl moiety, furnishing a one-pot three-component regioselective protocol suitable for preparing both isomers at moderate to excellent yields. The selectivity of the reaction was investigated through NMR analyses and the structures of the products were unambiguously determined by SCXR analyses.