Single fluoride substitution in trifluoromethylarenes is an ongoing synthetic challenge that often leads to "overreaction", where multiple fluorides are replaced. Development of this reaction would allow simple access to a vast range of difluoromethyl derivatives of current interest to pharmaceutical, agrochemistry, and materials sciences. Using a catalytic frustrated Lewis pair approach, we have developed a generic protocol that allows a single substitution of one fluoride in trifluoromethyl groups with neutral phosphine and pyridine bases. The resulting phosphonium and pyridinium salts can be further functionalized via nucleophilic substitution, photoredox coupling, and electrophilic transfer reactions allowing the generation of a vast array of difluoromethyl products.

We report the generation of aliphatic and benzylic acetylenes via reaction of primary, secondary, and tertiary aliphatic fluorides with various trimethylsilyl acetylides. These reactions are catalyzed by Al and B Lewis acids, most effectively by the extremely fluorophilic tris(pentafluorophenyl)alane, representing the first example of catalytic incorporation of alkynes into aliphatic C-F positions. The fluorophilicity of the catalysts gives rise to fluorine selectivity over other halogens, allowing orthogonal reactivity pathways.

We report frustrated Lewis pair (FLP)-catalyzed monoselective C–F activation in a range of aliphatic polyfluorocarbons with equivalent geminal and distal C–F positions. This methodology can be applied to aromatic-, ether-, thioether-, and alkyl-supported fluoromethyl groups. We expand the range of FLP base partners that work with monoselective C–F activation to include sulfide. The activated products can be subsequently functionalized via SN2 substitutions, photoredox-alkylations, and Suzuki couplings.

A method for aliphatic fluoride functionalization with a variety of nucleophiles has been reported. Carbon–fluoride bond cleavage is thermodynamically driven by the use of silylated pseudohalides TMS‐OMs or TMS‐NTf2, resulting in the formation of TMS‐F and a trapped aliphatic pseudohalide intermediate. The rate of fluoride/pseudohalide exchange and the stability of this intermediate are such that little rearrangement is observed for terminal fluoride positions in linear aliphatic fluorides. The ability to convert organofluoride positions into pseudohalide groups allows facile nucleophilic attack by a wide range of nucleophiles. The late introduction of the nucleophiles also allows for a wide range of functional‐group tolerance in the coupling partners. Selective alkyl fluoride mesylation is observed in the presence of other alkyl halides, allowing for orthogonal synthetic strategies.

Polyfluoromethyl groups generally suffer from over-reaction, where multiple C–F bonds are uncontrollably functionalized. The use of a frustrated Lewis pair (FLP)-mediated C–F bond activation permits selective monodefluorination through base capture of intermediate fluorocarbocations. FLP-mediated C–F bond activation can be applied to aromatic, heteroaromatic, or nonaromatic difluoro and trifluoromethyl groups to generate selectively fluoride-substituted phosphonium and pyridinium salts. These salts can be further functionalized by Wittig coupling, nucleophilic substitution, photoredox alkylation, nucleophilic transfer, or hydrogenation reactions to install a range of functional groups into the activated C–F position.1 Introduction2 Frustrated Lewis Pair C–F Activation3 Conclusion