Chemical properties of ylidene derivatives of azines. 4. Structures of the products of protonation and transformation of dihydroazinylidenecyanoacetic esters in concentrated sulfuric acid

It was demonstrated by UV and ¹³C NMR spectroscopy that in concentrated sulfuric acid ylidene derivatives of dihydropyridine (Ia) and dihydropyridazine (IIa) have aromatic structures Ib and IIb, while derivatives of dihydropyrimidines IIIa and IVa, dihydropyrazine Va, and dihydro-s-triazine VIa retain ylidene structures IIIb–VIb, respectively, which determines their greater stability in these solutions. When solutions of Ib–VIb in 95% H₂SO₄ were allowed to stand, they were converted to the corresponding azinylmalonic ester monoamides or azinylacetamides, depending on the reaction temperature.See 1] for communication 3.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 960–966, July, 1990.