Synthesis of Substituted Stilbenes via the Knoevenagel Condensation

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.

Potassium Phosphate as a Solid Base Catalyst for the Catalytic Transfer Hydrogenation of Aldehydes and Ketones

“…In reactions, K 3 PO 4 is more often used as a base in conjunction with homogeneous metal catalysts rather than as a catalyst in its own right. 36À39 However, a catalytic activity of K 3 PO 4 has been observed in the Knoevenagel condensation of cyanoacetates and malononitriles, 40 the decomposition of diacetone ABSTRACT: Potassium triphosphate is a surprisingly active catalyst for the catalytic transfer hydrogenation of carbonyl compounds. A pretreatment at 600 °C is critical to obtain the active material.…”

“…These exciting results prompted us to investigate the use of the readily available and mildly basic potassium phosphate (K 3 PO 4 ) for the catalytic transfer hydrogenation of aldehydes and ketones (Scheme ). In reactions, K 3 PO 4 is more often used as a base in conjunction with homogeneous metal catalysts rather than as a catalyst in its own right. − However, a catalytic activity of K 3 PO 4 has been observed in the Knoevenagel condensation of cyanoacetates and malononitriles, the decomposition of diacetone alcohol, the alkylation of toluene to ethylbenzene, and the cyanosilylation of carbonyl compounds . More recently, K 3 PO 4 has been reported as an efficient catalyst for the aminohalogenation of β-nitrostyrenes with N -bromoacetamide .…”

Strategies and Methods for the Syntheses of Natural Oligomeric Stilbenoids and Analogues

“…Al-Shihry (2004) [46] reported the synthesis of stilbene derivatives 51 (80%-95%) with electron withdrawing groups via Knoevenagel condensation (Scheme 2.21). This reaction is carried out between aldehyde 49 and activated methylene derivatives 50 in a polar solvent, ethanol added with K 3 PO 4 .…”

Enzymatic Tandem Approach to Knoevenagel Condensation of Acetaldehyde with Acidic Methylene Compounds in Organic Media

“…Knoevenagel condensation is one of the most important carbon–carbon bond‐forming reactions, used in the synthesis of chemically and pharmaceutically relevant compounds The Knoevenagel reaction products are also useful intermediates for further transformations, such as oxidative coupling reaction, Nazarov cyclization, Diels–Alder and Michael additions . This atom‐efficient reaction has been used to synthesize some interesting molecules, such as 4,7‐dihydroisoxazolo[5,4‐ b ]pyridines, coumarins, indanones, indenes, stilbenes, and azepinones . Generally, Knoevenagel condensations can be carried out in the presence of bases, Lewis acids, zeolites, clays, ionic liquids, or amino acids .…”