Enamino esters in the synthesis of heterocyclic systems. Transformation of diethyl acetone-1,3-dicarboxylate into poly-substituted 1,2,7,8-tetrahydro-2,7-naphthyridine-4-carboxylates

A simple three step synthesis of aminosubstituted 1,2,7,8-tetrahydro-2,7-naphthyridine-4- carboxylates is described. Ethyl (3-cyano-6-ethoxy-2-oxo-1,2-dihydropyridin-4-yl)acetate 3, formed by the condensation of diethyl acetone-1,3-dicarboxylate with malononitrile, was transformed with N,N-dimethylformamide dimethylacetal (DMFDMA) into (E)-ethyl 2-(3- cyano-6-ethoxy-2-oxo-1,2-dihydropyridin-4-yl)-3-(dimethylamino)propenoate 4. In further reaction the dimethylamino group was substituted with amino, hydroxy or substituted hydrazino group, followed by cyclisation to afford substituted 1-amino-7,8-dihydro-2,7-naphthyridine-4- carboxylate 6b, 1-imino-7,8-dihydro-1H-pyrano(3,4-c)pyridine-4-carboxylate 8, and 1-imino-2- aminosubstituted 1,2,7,8-tetrahydro-2,7-naphthyridine-4-carboxylates 13a-i.