L-PROLINE-CATALYZED KNOEVENAGEL CONDENSATION: A FACILE, GREEN SYNTHESIS OF (E)-ETHYL 2-CYANO-3-(1H-INDOL-3-YL)ACRYLATES AND (E)-3-(1H-INDOL-3-YL)ACRYLONITRILES

L-Proline has been utilized as a novel and ecofriendly catalyst in ethanol medium for the Knoevenagel condensation of indole-3-carboxyaldehydes and their N-methyl derivatives 1(a-e) and 4(a-e) with the active methylene compound, ethyl cyanoacetate (2) to afford substituted (E)-ethyl 2-cyano-3-(1H-indol-3-yl)acrylates 3(a-e) and 5(a-e) respectively. These products were reacted with dimethyl sulfate in the presence of PEG-600 as an efficient and green solvent to afford the corresponding N-mthylated derivatives 5(a-e). These Knoevenagel products react with 5% NaOH, yielding (E)-3-(1H-indol-3-yl)acrylonitriles 6(a-e) and 7(a-e).