Gem-Difluoromethylene group

Many varieties of fluorodesulfuration of protected (or activated) carbonyl compounds are known. Some contain an intermediate reductive step, leading to a wiorto-fluoromethylene instead of a gem-difluoromethylene group [146]. 

Urbina-Bianco CA, Skibinski M, O Hagan D, Nolan SP. Accelerating influence of the gem-difluoromethylene group in a ring-closing olefin metathesis reaction. A Thorpe-Ingold effect Chem Commun. 2013 49(65) 7201—7203. 

Nucleophiles therefore attack exclusively at the gem-difluoromethylene carbon of diflu-oroalkenes to form (3-fluorocarbanions (1). The chemical fates of 1 are mostly dependent on the structures of the alkenes and the reaction conditions. The typical reaction pathways of 1 are classified into three as shown in Scheme 2.17. In aprotic solvents, the carbanions (1) undergo defluorination, affording a-substituted monofluoroalkenes (2). Meanwhile, in pro tic solvents or in the presence of electrophiles in aprotic solvents, the carbanions (1) can be trapped with a proton or an electrophile to give addition products (3). The third case is S -type addition where substrates must have a leaving group on the y -carbon of 1 such as an alkoxy or an acyloxy group. 

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