Selective fluoroalkylation of organic compounds by tackling the "negative fluorine effect"

Abstract

The presence of fluorine on a carbanion center will dramatically influence the nucleophilic alkylation reactions. Based on our own experience, we noticed that the fluorine substitution on the carbanionic carbon poses a negative effect in many nucleophilic fluoroalkylation reactions [we propose this effect as "negative fluorine effect (NFE)"]. Two factors were believed to contribute to the NFE: (1) thermal instability of fluorinated carbanions caused by α-elimination (self-decomposition) and (2) the intrinsic nucleophilicity of fluorinated carbanion influenced by the fluorine atoms (such as hard/soft nature of the fluorinated carbanions). By tackling the NFE, our research group has attempted to design nucleophilic fluoroalkylation reactions with fluorinated sulfones and related reagents. These results were summarized as four methods to modulate the fluoroalkylation reactions: (1) changing the number of fluorine atoms, (2) slightly changing the neighboring groups, (3) changing the metal counterion, including using carbon-metal covalent bond to tune the reactivity, and (4) enhancing the generation of carbene species.