Stabilization of (N-methyleneamino)imidoylketenes: synthesis of dipyrazolo[1,2-a;1′,2′-d][1,2,4,5]tetrazines

Thermolysis of substituted methyl 1-methyleneamino-4,5-dioxo-4,5-dihydro-1H-pyrrole-2-carboxylates led to substituted dimethyl 3,9-dioxo-1,5,7,11-tetrahydro-1H,7H-dipyrazolo[1,2-a;1′,2′-d][1,2,4,5]tetrazine-1,7-dicarboxylates and methyl 2,5-dihydro-5-oxo-1H-pyrazole-3-carboxylates as minor products. The structure of compound was determined by X-ray crystallography. The proposed mechanism of this conversion includes generation of (N-methyleneamino)imidoylketenes and its intramolecular transformation to azomethine imines—5-oxo-2,5-dihydropyrazole-1-methylium-2-ides , which undergo dimerization in head-to-tail manner yielding products and partially hydrolyse to compounds .