Synthesis of Pyridopyrimidines by Palladium-Catalyzed Isocyanide Insertion

A new synthetic approach to 4-aminopyrido­[2,3-d]­pyrimidines and 4-aminopyrido­[3,2-d]­pyrimidines based on palladium-catalyzed reaction of isocyanides with readily available N-(bromopyridyl)­amidines is reported. The target heterocycles were obtained in generally good to excellent yield. For the two regioisomeric pyrimidopyrimidines, we compared our approach involving oxidative addition with the analogous C–H activation protocol because both methods have been reported for the synthesis of 4-aminoquinazolines. We found that the C–H activation protocol does not allow one to obtain the target pyridopyrimidines, but the imidoylative cross-coupling protocol provided a new entry to the synthesis of these medicinally important scaffolds.