Phosphonium fluorides esters

Recently, an interesting method involving an intramolecularly assisted dchydrolluorination, mediated by (benzotriazol-l-yloxy)tris(dimethylamino)phosphonium hexafluorophosphate (BOP), was described.37 The reaction proceeds via a hydrobenzotriazole ester intermediate followed by concerted intramolecular elimination of hydrogen fluoride. 

Synthesis of trifluoromethylated compounds 152 has been achieved via ester-enolate [2,3]-Wittig and [3,3]-lreland-Claisen rearrangements. Perfluorocyclo-butane phosphonium ylides, e.g. 153, have been used as a masked fluoride anion source in their reactions with alcohols and carboxylic acids which lead to alkyl-and acyl-fluorides. Ylides 153 are also reported to cleave Si-C and Si-O bonds, cause dimerisation of fluoro-olefins, and also react with acid chlorides or other activated aromatic compounds under halogen exchange. ... 

---