PPh₃-catalyzed knoevenagel condensation: A facile synthesis of 5-(1H-indol-3-yl)Meth- ylene)-2, 2-Dimethyl-1, 3-Dioxane-4, 6-dione, and their N-alkyl derivatives by using peg-600 as the reaction medium

Triphenylphosphine (TPP) has been utilized as a novel and efficient catalyst for the Knoevenagel condensation of indole-3-carboxaldehydes 1(a–e), 1-methyl-1H-indole-3-carboxaldehydes 4(a–e), and 1-ethyl-1H-indole-3-carboxaldehydes 6(a–e) with the active methylene compound, that is, meldrum's acid (2), to afford substituted derivatives 5-((1H-indol-3-yl) methylene)-2,2-dimethyl-1,3-dioxane-4,6-dione 3(a–e), 2,2-dimethyl-5-((1-methyl-1H-indol-3-yl)methylene)-1,3-dioxane-4,6-dione 5(a–e), and 2,2-dimethyl-5-((1-ethyl-1H-indol-3-yl)methylene)-1,3-dioxane-4,6-dione 7(a–e), respectively, in ethanol medium at RT just within 1 h in excellent yields. The products 3(a–e) were reacted independently with alkylating agents, that is, DMS and DES in the presence of PEG-600 as an efficient and green solvent, to afford the corresponding N-substituted methyl and ethyl derivatives 5(a–e) and 7(a–e), respectively. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 23:41–48, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.20750