An investigation on synthesis and spectroscopic properties of Hantzsch type 1,4-dihydropyridine derivatives

Preparation of the Hantzsch type 1,4-dihydropyridine derivatives, i. e. 1 , 2 , 6-trimethyl-4-aryl-3, 5-dicarbethoxy-1,4-dihydropyridines 2a-2f, 4-ary l-2 , 6-diphenyl-3,5-dicarbethoxy-1, 4-dihydropyridines 3a-3f and their N-m ethylated compounds 4a-4f was described (aryl : p-RC6H4-; R = OCH3, CH3, H, Cl, CN, NO2). The 4-aryl-2 , 6-dimethyl-3, 5-dicarbethoxy-1, 4-dihydropyri dines 1a-1f show a relative strong fluorescence, whereas under the same con ditions, compounds 3a-3f give a weak fluorescence. No fluorescence was obse rved for N-methylated compounds 2a-2f, 4a-4f. In H-1 NMR spectra the methyl protons at the 1-position in 4a-4f are shifted unfield by delta = 0. 6 sim ilar to 0. 7 compared to those in 2a-2f. The above observations were ration alized in terms of the conformational changes resulting from the steric int eractions among the substitutents in the dihydropyridine ring.