New aspects on the selective synthesis of 7-arylpyrido[2,3-d]pyrimidines

Pyrido[2,3-d]pyrimidines have been synthesized via a selective cyclocondensation reaction between 6-aminopyrimidines and the Mannich bases, propiophenone hydrochlorides . Intermediates for this reaction, such as the Michael addition adduct and the further hydrated pyrido[2,3-d]pyrimidine were isolated to prove the postulated mechanism. NMR analysis of bidimensional experiments allowed to determine unambiguously the process to obtain 7-arylpyrido[2,3-d]pyrimidines.