Preparation of 5-Fluoropyrazoles from Pyrazoles and N-Fluorobenzenesulfonimide (NFSI).

Facile synthesis of 5-fluoropyrazoles by direct fluorination of pyrazoles with N-fluorobenzenesulfonimide (NFSI) was elaborated. This approach was used to prepare the unsubstituted 5-fluoro-1 H-pyrazole, the known fungicide Penflufen, and many functionalized 5-fluoropyrazoles: building blocks for medicinal chemistry and agrochemistry.