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-triaz ines 7 and pyrido[1,2-b]pyridazines 8 respectively by cycloacylation of der ivatives of pyridine with imidoylchlorides of type 2 is described. The hete rocycles of type 6 as well as of type 7 can be ring-transformed with dimeth yl acetylenedicarboxylate. In contrast to pyrido[1,2-a]pyrazines 1, a compl ex reaction including cleavage of the acetylene subunit takes place. Starti ng 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 q uantitatively the tricyclic products of type 12.