Addition reactions of heterocyclic compounds. Part 68. The conversion of 1,6-dihydropyridines into benzene derivatives with dimethyl acetylenedicarboxylate

Abstract

3-Carbamoyl- and 3-cyano-1-methyl-1,6-dihydropyridine, and the 3-carbamoyl-1-benzyl- and -1-phenylanalogues, with dimethyl acetylenedicarboxylate undergo successive Diels–Alder addition and retrogression giving the corresponding dimethyl phthalates. Other enamine-type additions to the acetylene, and displacement of the carbamoyl group by a cis-(1,2-bismethoxycarbonylvinyl) group, occur with these 1,6- and also 1,2- and 1,4-dihydropyridines. The structures of the adducts were deduced mainly from their ¹H n.m.r. spectra.