Tandem [4+2] cycloaddition versus electrocyclisation reactions of 1-aryl-2-phenyl-5-alkyl/aryl-1,3-diazapenta-1,3,4-trienes in aza-Wittig reactions of N′-aryl-N-(triphenylphosphoranlidene) benzenecarboximidamides with ketenes

1-Aryl-2-phenyl-5-alkyl/aryl-1,3-diazapenta-1,3,4-triene 3 generated in situ aza-Wittig reactions of N′-aryl-N-(triphenylphosphoranylidene)carboximidamides 1 which are shown to undergo selective [4+2] cycloaddition and electrocyclisation reactions leading to the formation of novel pyrimidinone derivatives 5 and quinazoline derivatives 7 with monosubstituted ketenes and diphenylketene, respectively.