Fused pyrimidine systems: XV. Intramolecular electrophilic cyclization of 2-allyl(propargyl, cinnamyl)amino-pyrido[2,3-d]pyrimidin-4(3H)-ones

2-(Allylamino)- and 2-(propargylamino)pyrido[2,3- d ]pyrimidin-4(3 H )-ones underwent intramolecular cyclization on heating in polyphosphoric acid to give angularly fused imidazo[1,2- a ]pyrido[3,2- e ]pyrimidin-5-ones. The cyclization of 2-(cinnamylamino)pyrido[2,3- d ]pyrimidin-4(3 H )-one under analogous conditions afforded linearly fused 4-phenyl-1,2,3,4-tetrahydro-6 H -pyrido[2,3- d ]pyrimido[1,2- a ]pyrimidin-6-one. 2-(Allylamino)pyrido[2,3- d ]pyrimidin-4(3 H )-one reacted with iodine yielding 9-(iodomethyl)-8,9-dihydroimidazo[1,2- a ]pyrido[3,2- e ]pyrimidin-5(7 H )-one as the major product, 2-(propargylamino)pyrido[2,3- d ]pyrimidin-4(3 H )-one gave rise to iodine addition product to the triple bond, and angularly fused 9-iodo-10-phenyl-7,8,9,10-tetrahydro-5 H -pyrido[3,2- e ]pyrimido[1,2- a ]pyrimidin-5-one was obtained from the 2-(cinnamylamino) derivative. Electrophilic cyclization of 2-(allylamino)- and 2-(cinnamylamino)pyrido[2,3- d ]pyrimidin-4(3 H )-ones by the action of phenylsulfanyl chloride led to the formation of angularly fused 9-(phenylsulfanylmethyl)-8,9-dihydroimidazo[1,2- a ]pyrido[3,2- e ]pyrimidin-5(7 H )-one and 10-phenyl-9-phenylsulfanyl-7,8,9,10-tetrahydro-5 H -pyrido[3,2- e ]pyrimido[1,2- a ]pyrimidin-5-one.