Synthesis of some new thiazolo[3,2-a]pyrido[2,3-d]pyrimidinones and isoxazolo[5′,4′:4,5]thiazolo[3,2-a]pyrido[2,3-d]pyrimidinone

6-Amino-2,3-dihydro-2-thioxo-4(1H)-pyrimidinone I reacts in boiling DMF with a cyclic alpha, beta-unsaturated ketones 2 affording the pyrido [2,3-d]pyrimidinone 6a,b, the latter compound condensed with aldehyde in presence of chloroacetic acid to yield thiazolo[3,2-a] pyrido [2,3-d]-pyrimidinones (7, 8) respectively. The alkylation of pyrido-pyrimidinone it gave the 2-alkylthio derivatives 10a-e, compound 10b cyclized to thiazolopyridopyrimidinone derivative 13. Also, the condensation of compounds 7a,b with hydoxylamine gave the corresponding isoxazolo[5',4':4,5]thiazolo[3,2-a]pyrido[2,3-d]pyrimidinone.