Synthesis and reactions of α-fluorovinylphosphonium salts

The alpha-fluorovinyltriphenylphosphonium triflate 4 is prepared in high yields by the diphenylphosphinylation of 1,1-difluoroethylene 1 and subsequent quaternization of the phosphine 2 with diphenyliodonium triflate in the presence of CuCl. The salt 4 then undergoes Michael addition followed by Wittig olefination to give the corresponding monofluoroethylene compounds in good yields. The reaction of 4 with the caesium salts of salicylaldehyde derivatives in DMF at 130 degrees C affords the corresponding monofluorinated chromenes in a one-pot synthesis. The hydrolysis of 4 in the presence of sodium hydroxide gives triphenylphosphine oxide in quantitative yield.