Synthesis of bromodifluoromethyl substituted pyrazoles and isoxazoles

Bromodifluoromethyl substituted β-diketone 3a–3d, prepared from corresponding ketones and ethyl bromodifluoroactate in the presence of sodium methoxide, reacted with aryl hydrazine derivatives affording bromodifluoromethyl substituted pyrazoles in high regioselectivity. The reaction of 3a–3d with hydroxylamine hydrochloride gave dihydroisoxazoles, which afforded bromodifluoromethyl substituted isoxazoles through dehydration by PPA or concentrated sulfuric acid.