Application of the intramolecular aza-Wittig reaction to the synthesis of pyrido[2,3-d]pyrimidines

Pyrido[2,3-d]pyrimidines are synthesized in a two-step procedure from amides and tetrazolo[1,5-a]pyridine-8-carbonyl chloride. Reaction of the crude imides with triphenylphosphine effects an intramolecular aza-Wittig reaction to afford a variety of substituted pyrido[2,3-d]pyrimidines in good to moderate yields (30–76%).