New heterocycles with cycloamidine substructure and their ringtransformation reactions with acetylene dicarboxylic ester

The synthesis of pyrido[2,1-c]-1,2,4-triazines 6, pyrido[1,2-b]-1,2,4-triazines 7 and pyrido[1,2-b]pyridazines 8 respectively by cycloacylation of derivatives of pyridine with imidoylchlorides of type 2 is described. The heterocycles of type 6 as well as of type 7 can be ring-transformed with dimethyl acetylenedicarboxylate. In contrast to pyrido[1,2-a]pyrazines 1, a complex reaction including cleavage of the acetylene subunit takes place. Starting from compound 6a, the pyrrolo[2,3-d]imidazole 11a could be isolated from a mixture of unidentified by-products, whereas derivatives 7 gave nearly quantitatively the tricyclic products of type 12.