Abstract: 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-aryl -2,6-diphenyl-3,5-dicarbethoxy-1,4-dihydropyridines 3a_3f and their Nmethylated 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-dihydropyridines 1a_1f show a relative strong fluorescence, whereas under the same conditions, compounds 3a_3f give a weak fluorescence. No fluorescence was observed for N-methylated compounds 2a_2f, 4a_4f. In ¹HNMR spectra the methyl protons at the 1-position in 4a_4f are shifted unfield by δ= 0.6～0.7 compared to those in 2a_2f. The above observations were rationalized in terms of the conformational changes resulting from the steric interactions among the substitutents in the dihydropyridine ring.

Key words: 1,4-Hantzsch dihydropyridine derivatives, Synthesis, 1,4-Dihydropyridine ring conformation, ¹HNMR, Fluoresence spectrum