Rearrangement reactions of dimethyl 2,7-dimethyl-3H-azepine-3,6-dicarboxylate

Abstract

The base-catalysed reaction of dimethyl 4-chloromethyl-1,4-dihydro-2,6-dimethylpyridine-3,5-dicarboxylate to derivatives of both 4H- and 3H-azepines can be reversed by hydrochloric acid. Dimethyl 2,7-dimethyl-3H-azepine-3,6-dicarboxylate rearranges to methyl (5-methoxycarbonyl-2,6-dimethyl-3-pyridyl)acetate under the action of either sodium methoxide or mineral acids. With ethanolic hydrochloric acid, two other products have been identified from the azepinedicarboxylate, the original 4-chloromethyl-1,4-dihydropyridine and a hydroxy-dihydroazepine. The action of N-bromosuccinimide on dimethyl 4,5-dihydro-2,7-dimethyl-1H-azepine-3,6-dicarboxylate yields a lactone formed by bromination of a nuclear methyl group followed by cyclisation with an adjacent ester group.