Synthesis and regioselective [4+2] cycloaddition/nucleophilic reactions of N-arylamino-1:3-diaza-1:3-butadienes with ketenes and accompanying rearrangements

N-Arylamino-1:3-diaza-1:3-butadienes 4 are shown to undergo regioselective reactions with phenyl- and chloroketenes resulting in high yields of 3-aryl-2-methylthio6-phenyl-4(3H)-pyrimidinones 7. Similar reactions with bromo- and iodoketenes, resulted, via aziridinium intermediates 12, in good yields of 3-aryl-S-(N-arylamino)-2-methylthio-6-phenyl4(3H)-pyrimidinones 13, The mechanistic aspects of cycloadditions and semi-empirical AM1 calculations for these diazabutadienes are also reported.