Wittig Olefination via Reaction of Fluorine-Containing Phosphoranium Salts and F-Acyl Fluorides. A New Approach to Fluoroolefin Synthesis

摘要

Flourine-containing phosphoranium salts such as BU3P(+)-CFP(+)Bu3X(-) and PH3P(+)Ph3Br(-) were readily prepared from tertiary phosphines and CFCl3 and CFBr3. In contrast to the normal acylation of phosphonium ylides by acyl halides, Bu3P(+)-CFP(+)Bu3X(-) undergoes a Wittig reaction with F-acyl fluorides to give stereospecifically the trans-vinyl phosphonium salts, Bu3P(+)CF-CFR sub Fx(-) double bond. Alkaline hydrolysis of the phosphonium salt gives the trans-1-hydro-F-olefin. The overall one-pot process provides a novel stereospecific conversion of F-acyl halides to olefins with chain-extention of one carbon. Mechanistically, the process demonstrates that with proper control, the reaction of phosphonium ylides with acyl halides can be diverted to olefination rather than the previously observed acylation sequence.