Synthetic Approaches to gem-Difluoromethylene Compounds

Organic compounds containing a gem-difluoromethylene group are useful for a variety of applications in biological, pharmaceutical and materials chemistry. Over the years a variety of synthetic protocols for this class of compounds have been developed. They can be prepared from their corresponding carbonyl compounds or through various derivatives such as oximes and dithiolanes, electrophilic fluorinations of unsaturated compounds and enolates, free-radical additions of halodifluoroalkanes to olefins, and nucleophilic difluoromethylations of aldehydes and ketones. Other approaches involve methods that utilize fluorinated compounds as synthons. Enantioselective gemdifluorination reactions have emerged employing chiral auxiliaries such as sulfinimines, and chiral Lewis acid catalysts. This review focuses on the recent developments in this area, emphasizing the synthetic methods that can be conveniently carried out and are potentially broadly applicable.