The preparation of dimethyl 4-(1-chloroethyl)-1,4-dihydro-2,6-dimethylpyridine-3,5-dicarboxylate and its reaction with nucleophilic reagents are described. Potassium cyanide, potassium succinimide, or methanolic triethylamine gave, stereospecifically, 4,5-dihydroazepines in which substituents at C(4) and C(5) aretrans, whereas potassium thiocyanate afforded only the corresponding 4-(1-thiocyanatoethyl)-1,4-dihydropyridine. Sodium hydrosulfide afforded a mixture of 8-thia-2-azabicyclo[3.2.1]oct-3-ene-4,7-diesters epimeric at C(7), whereas potassium carbonate in aqueous dimethyl sulfoxide yielded an 8-oxa-2-azabicyclo-[3.2.1]oct-3-ene-4,7-diester. The stereochemistry of these bicyclic compounds is established using nmr spectroscopy. In acid media, dimethyl 2,5,7-trimethylazepine-3,6-dicarboxylate and a 4-methoxy-4,5-dihydroazepine rearranged to give 1,4-dihydropyridine derivatives; a mechanism for this ring contraction is suggested.