Microwave‐mediated pyrazole fluorinations using selectfluor®

Abstract Microwave‐mediated electrophilic fluorinations and a new single‐pot condensation en route to ring‐fluorinated pyrazoles were examined: magnified image The monofluorination by these methods was successful for a variety of pyrazoles, with yields ranging from 13% to 75%. While electrophilic aromatic fluorination of 3‐CF 3 pyrazoles proved largely ineffective, development of a single‐pot process overcame this limitation. The microwave‐mediated reaction is regioselective; ring fluorination of the heterocycle occurs preferentially over phenyl and alkyl substituents. Alkyl side chain fluorination, when desired, can be modulated by reactant ratios. The single‐pot method, which involves acid catalysis by H‐TEDA, produces 4‐fluoropyrazoles products. © 2009 Wiley Periodicals, Inc. Heteroatom Chem 20:341–345, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20556