1,5-Phosphonium betaines from -triflylpropiolamides, triphenylphosphane, and active methylene compounds.

-Phenyl--(trifluoromethylsulfonyl)propiolamides react with triphenylphosphane in the presence of various active methylene compounds CHXY in a 1:1:1 molar ratio to furnish 1-phosphonium-5-oxabetaines, PhP-C(R)=CH-C(O)=CXY. These betaines are formed preferentially, but not exclusively, as -diastereoisomers with respect to the vinylic double bond. In some cases, separation of the two diastereoisomers was achieved by fractionating crystallization.