An Efficient and General Method for the Reformatsky-Type Reaction of Chlorodifluoromethyl Ketones with Carbonyl Compounds Giving α,α-Difluoro-β-hydroxy Ketones

Chlorodifluoromethyl ketones CF2ClCOR, where R is an alkyl, aryl, and 1-alkynyl group, underwent the Reformatsky-type aldol reaction with a wide variety of aldehydes or ketones in the presence of acid-washed zinc dust and copper(I) chloride or silver acetate to give the corresponding α,α-difluoro-β-hydroxy ketones in good to excellent yields. Specific activation of zinc metal with the metal salt is essential to achieve high efficiency of the reaction, depending upon the structures of the chlorodifluoromethyl ketones and the carbonyl compounds employed. In-situ formed intermediates in these reactions were successfully detected by 19F NMR spectroscopy, which suggests that their structure is not an α-metallo ketone but an oxygen-metallated species possessing the zinc(II) metal as counter cation.