Addition reactions of heterocumulenes. III. Reaction of diketene with formamidine derivatives.

Reaction of several conjugated C-N double bond compounds with diketene was carried out with a view to establishing the structure-reactivity relationship of the 1, 3-diaza-1, 3-butadiene system. Formamidine derivatives (IIIa-h) reacted with diketene in benzene to form the products (Va-h) through 1, 4-dipolar cycloaddition with the elimination of dimethylamine, respectively. Similarly, reaction of diketene with 2-(p-dimethylaminobenzylideneamino) benzothiazole (IXa) and 2-(p-dimethylaminobenzylideneamino) benzimidazole (IXb) respectively afforded 3-acetyl-2-(p-dimethylaminophenyl)-2, 3-dihydro-4-oxo-4H-pyrimido [2, 1-b] benzothiazole (Xa) and 3-acetyl-2-(p-dimethylaminophenyl)-2, 3-dihydro-4-oxo-4H-pyrimido-[1, 2-a] benzimidazole (Xb).