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

N -Phenyl- N -(trifluoromethylsulfonyl)propiolamides react with triphenylphosphane in the presence of various active methylene compounds CH 2 XY in a 1:1:1 molar ratio to furnish 1-phosphonium-5-oxabetaines, Ph 3 P + –C(R)=CH–C(O – )=CXY. These betaines are formed preferentially, but not exclusively, as E -diastereoisomers with respect to the vinylic double bond. In some cases, separation of the two diastereoisomers was achieved by fractionating crystallization. Structure determination by X-ray diffraction analysis revealed marked conformational differences around the CH–C(O – ) single bond of E and Z -isomers and extended charge delocalization in the anionic part.

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