L-Proline-Catalyzed Knoevenagel Condensation:A Tandem Synthesis of 3-Acetylcoumarinoindoles and Their N-Alkyl Derivatives by Using PEG-600 as the Reaction Medium

摘要

Atandem synthesis of 3-acetylcoumarinoindoles 5(a-e) in the presence of catalytic amount of L-proline in ethanol medium is reported. L-proline has been utilized as an efficient and eco-friendly catalyst for the Knoevenagel condensation of 3-cyanoacetylindoles 1(a-e) with 2-hydroxybenzaldehyde (2) to afford the corresponding substituted 3-(1H-indol-3-yl)2-(2-hydroxybenzylidene)-3-oxopropanenitriles 3(a-e), which without isolation were treated with hot conc. HCl to afford 3-acetylcoumarinoindoles 4(a-e) in high yields. Subsequently, these were reacted with dimethyl sulfate in the presence of PEG-600 (Hyderabad, Andhra Pradesh, India) as an efficient and green solvent to afford the corresponding N-methyl-3-acetylcoumarinoindoles 5(a-e) in moderate yields.