Simple and efficient Knoevenagel synthesis of (E)-2-((1H-indol-3-yl)

methylene)-3-oxoindolylnitrile catalysed by PPh₃

M VENKATANARAYANA^* and P K DUBEY

Department of Chemistry, Jawaharlal Nehru Technological University, Hyderabad College of Engineering,

Kukatpally, Hyderabad 500 085, India

e-mail: venkatmuvvala@in.com

MS received 17 November 2010; revised 31 July 2011; accepted 1 August 2011

Abstract. Triphenylphosphine (TPP) is found to be an efficient catalyst for the Knoevenagel condensation of

indole-3-carboxyaldehydes 1(a–e) and their N-substituted derivatives 4(a–e) with the active methylene compound,

i.e., 3-cyanoacetylindole (2), affording novel substituted olefins 3(a–e) and 5(a–e) respectively. The

latter products reacted with DMS in the presence of PEG-600 to afford the corresponding N, N^l dimethylated

derivatives 6(a–e).

Graphical Abstract. Triphenylphosphine (TPP) is found to be an efficient catalyst for the

Knoevenagel condensation of indole-3-carboxyaldehydes 1(a–e) and their

N-substituted derivatives 4(a–e) with the active methylene compound, i.e.,

3-cyanoacetylindole (2), affording novel substituted olefins 3(a–e) and 5(a–e)

respectively. The latter products reacted with DMS in the presence of PEG-600

as an efficient and green solvent to afford the corresponding N, N^l dimethylated

derivatives 6(a–e).

Keywords. Indole-3-aldehydes; 3-cyanoacetylindole; PPh3; Ethanol; PEG-600; DMS