Abstract: Pyrido [2, 3-d] pyrimidine derivatives 5 were synthesized by the intermolecular aza- Wittig reaction of 2-(triphenylphosphoranylidene) aminonicotinamides 3 derived from 2- aminonicotinic acid (1), with carboxylic acid chloride followed by heterocyclization via imidoyl chloride intermediate 4. The structure of 3-allyl-2-(4-nitrophenyl)-4 (3H)-pyrido [2, 3- d] pyrimidinone (5b) was established by X-ray crystallographic analysis. This methodology ...