Synthesis and [4+2] cycloaddition reactions of 4-(N-allyl-N-aryl)amino-1,3-diaza-1,3-butadienes with vinyl-, isopropenyl- and chloroketenes: Entry to novel pyrimidinone/fused pyrimidinone derivatives

4-(N-Allyl-N-aryl)amino-1,3-diaza-1,3-butadienes 2, prepared by the treatment of N-arylamino-1,3-diaza-1,3-butadienes 1 with allyl bromide, underwent [4+2] cycloadditions with vinyl/isopropenyl- and accompanied by rearrangements in case of chloroketenes, to yield 5-vinyl/isopropenyl pyrimidinones 5 and 5-methylthio pyrimidinones 19, respectively. The pyrimidinones 5 on refluxing in xylene gave pyrimidoazepines 6, underwent annelation reaction, in refluxing benzene in presence of AlCl₃, to yield pyrimidoquinolines 7 and on treatment with DMAD in refluxing toluene, underwent [4+2] cycloaddition accompanied by the elimination of N-allylarylamine functionality to yield quinazolinone 9. Further, the reactions of 5 with PhSH in the presence of AIBN in refluxing benzene followed unusual radical cyclisation involving N-aryl group leading to pyrimidoquinolines 10. The iodocyclisation of pyrimidinones 19 yielded pyrimidothiazines 20.