Fused pyrimidine systems: XIII. Synthesis and some transformations of 1,3-thiazolo(thiazino)-fused pyrido[3,4-d]pyrimidines

2-[Allyl(propargyl)sulfanyl]pyrido[3,4- d ]pyrimidin-4-ones at heating in polyphosphoric acid undergo an intramolecular cyclization with the formation of pyrido[4,3- e ]thiazolo-[3,2- a ]pyrimidin-5-ones of angular structure. Under similar conditions the cyclization of 2-(cinnamylsulfanyl)pyrido[3,4- d ]-pyrimidin-4-one results in a linear pyrido[3′,4′:4,5]pyrimido-[2,1- b ][1,3]thiazin-6-one. The iodocyclization of the same substrates affords the corresponding 9-(iodomethyl)(iodomethylidene)pyrido[4,3- e ][1,3]thiazolo-[3,2- a ]pyrimidin-5-ones and 3-iodopyrido[3′,4′:4,5]pyrimido[2,1- b ][1,3]thiazin-6-one of angular structure. 9-(Iodomethyl)-8,9-dihydro-5 H -pyrido[4,3- e ][1,3]thiazolo[3,2- a ]pyrimidin-5-one treated with sodium azide gave 9-(azidomethyl) derivative whose cyclization with substituted alkynes in the presence of copper compounds provided pyrido [4,3- e ][1,3]thiazolo[3,2- a ]pyrimidinylmethyltriazoles.