Dehydrogenation of 5,6-Dihydropyrido[3,2-d]pyrimidin-7(8H)-ones: A Convenient Last Step for a Synthesis of Pyrido[2,3-d]pyrimidin-7(8H)-ones

Two new protocols for the dehydrogenation of 5,6-dihydropyrido[2,3-d]pyrimidin-7(8H)-ones to pyrido[2,3-d]pyrimidin-7(8H)--ones are described. The first one uses NaH in DMSO an affords the corresponding pyridopyrimidines when an aryl substituent is present at C6. The second one is of a more general use, allowing dehydrogenation of aryl and alkyl substituted 5,6-dihydropyridopyrimdines upon treatment with Na 2 Se0 3 in DMSO.