In situ generated stabilized phosphorus ylides mediated a mild and efficient method for the preparation of some new sterically congested electron-poor N-vinylated heterocycles

Protonation of the highly reactive 1:1 intermediate produced in the reaction between triphenylphosphine and an acetylenic ester by a N-H acid (4-phenylphthalazin-1(2 H)-one, 5,5-diphenylimidazolidine-2,4-dione) leads to the formation of a vinyltriphenylphosphonium salt. The cation of the salt undergoes an addition reaction with the counter anion in CH₂Cl₂ at room temperature to yield the corresponding stabilized phosphorus ylide. Elimination of triphenylphosphine from the stabilized phosphorus ylides leads to the formation of corresponding electron-poor N-vinylated heterocycles in moderate to high yields (67–95%). The reaction is completely regio- and stereoselective.