synthesis of substituted stilbenes via the knoevenagel condensation通过诺文葛耳缩合合成对称二苯代乙烯代替.pdf

Molecules 2004, 9, 658–665 molecules ISSN 1420-3049 Synthesis of Substituted Stilbenes via the Knoevenagel Condensation Shar Saad Al-Shihry Department of Chemistry, College of Science, King Faisal University, P.O. Box 1759, Hofuf 31982, Saudi Arabia; Tel.: (+966) Fax: (+966) E-mail: sshihry@.sa. Received: 15 January 2004; in revised form: 4 July 2004 / Accepted: 8 July 2004 / Published: 31 July 2004 Abstract: Knoevenagel condensations between aldehydes and substrates containing active methylene groups were carried out in ethanol at room temperature, in the presence of potassium phosphate, to afford unsymmetrical olefins. These condensations have been shown to afford only the E-isomers in greater than 80% yields. Salicylaldehyde first produces the Knoevenagel condensation products, which undergo a subsequent heterocyclization to give coumarin derivatives. The structures of the synthesized compounds were established on the basis of UV, IR, MS and NMR spectroscopy. Keywords: Knoevenagel condensation; E-stilbenes; coumarins; potassium phosphate. Introduction The Knoevenagel condensation has been extensively studied and has been used for the preparation of a broad spectrum of substituted alkenes. This condensation may be carried out in various homogeneous media using catalysts such as piperidine [1,2], amines, ammonia, and ammonium salts [3-5]. In recent years much attention has been focused to use of natural inor