Photolysis of 2,6-dimethyl-3,5-dicarboethoxy- 1,4-dihydropyridine-4-carboxylic acid

The photolysis of 2,6-dimethyl-3,5-dicarboethoxy-1,4-dihydropyridine-4-carboxylic acid 1 gives with a pyrex filter pyridine 2 and glycol 3. At low concentration, aldehyde 4 accumulates. The photochemical dimerization of this aldehyde gives glycol 3 in methanol or ethanol. The aldehydic hydrogen in aldehyde 4 is replaced by deuterium on performing the photolysis of acid 1 in MeOD as is the case for the photolysis of 2,6-dimethyl-3,5-diacetyl-1,4-dihydropyridine. A concerted mechanism for the decarboxylation of acid 1 to aldehyde 4 is possible. When the photolysis of 1 is performed in quartz, another reaction occurs leading to 1,2-dihydropyridine 8.