Efficient Access to Functionalized N‑Difluoromethylpyrazoles

Fluorinated pyrazoles play important roles in medicinal chemistry, drug discovery, agrochemistry, and coordination chemistry. Although fluorinated compounds have many benefits, the preparation of functionalized fluorinated pyrazoles, partly N-difluoromethylpyrazoles, remains challenging. Here, selective oxidation of the methyl group in 1-(difluoromethyl)-3-methyl-1H-pyrazole and 1-(difluoromethyl)-5-methyl-1H-pyrazoles to prepare the corresponding pyrazole-3- and pyrazole-5-carboxylic acids was described. The carboxylic acids were transformed into a broad range of new functionalized derivatives: esters, alcohols, aldehydes, amines, amides, nitriles, and chloro derivatives. The crystal structure of the initial carboxylic acid derivatives has been determined from single-crystal X-ray analysis, which provided unambiguous proof of the regiochemistry of all prepared 1-difluoromethyl-pyrazoles. Note, in the crystalline structure of substituted pyrazole-3-carboxylic acid, the formation of dimers via double hydrogen bonds of O-H···O between molecules was observed, while the pyrazole-5-carboxylic acid derivative forms chains via hydrogen bonds of O-H···N_Pz.