for the following products
3,5-Diethoxycarbonyl-1,4-dihydro-2,4,6-collidine | 3,5-Diethyl 2,4,6-trimethyl-1,4-dihydropyridine-3,5-dicarboxylate | Diethyl 1,4-dihydro-2,4,6-trimethyl-3,5-pyridinedicarboxylate and 3,5-Dicarbethoxy-1,4-dihydro-2,4,6-trimethylpyridine
