Mild and Facile Cleavage of 2-Cyanoethyl Ester Using Sodium Sulfide or Tetrabutylammonium Fluoride. Synthesis of 1,4-Dihydropyridine Monocarboxylic Acids and Unsymmetrical 1,4-Dihydropyridine Dicarboxylates

Several 3-(2-cyanoethyl)-1,4-dihydropyridine carboxylates (16) were prepared in moderate to good yields by means of the Hantzsch reaction. Treatment of these carboxylates with a weak base such as sodium sulfide or tetrabutylammonium fluoride at room temperature afforded smoothly the corresponding 1,4-dihydropyridine monocarboxylic acids (18) in good yields. The monocarboxylic acids 18n and 18o were esterified with 2-nitrooxypropanol or N-(2-hydroxyethyl)nicotinamide p-toluenesulfonic acid salt to afford the selective coronary vasodilators CD-349 (5) and CD-832 (6), respectively.