Knoevenagel condensation Alumina

Keywords aldehyde, ketone, active methylene compound, Knoevenagel condensation, basic alumina, microwave irradiation, olefin... 

A three-component reaction of aromatic aldehydes, malononitrile and phenols leads to 4-aryl-2-amino-3-cyano-4//-chromenes this reaction can be carried out in aqueous media with improvements in yield and obvious environmental advantages (Scheme 35). The aromatic aldehyde undergoes a Knoevenagel condensation with malononitrile, followed by ortho-alkylation of the phenol and cyclization to form the iminopyran intermediate 114, which isomerizes to the 4//-chrorncncs (Scheme 36) <2003SL2001>. High yields for this three-component reaction can also be achieved in aqueous media when mediated by 7-alumina <2004TL2297> or cetyltrimethylammonium chloride <2001T1395>. 

Condensations. Alumina promotes the formation of a-hydroxyphosphonate esters from aromatic aldehydes and dialkyl phosphonates, and the adducts are converted to a-aminophosphonate esters on reaction with ammonia. A solvent-free synthesis of a-nitro ketones comprises mixing nitroalkanes, aldehydes, and neutral alumina and oxidizing the adducts with wet, alumina-supported CrOj (15 examples, 68-86%). The Knoevenagel reaction, the Michael addition of nitromethane to gcm-diactivated alkenes, and the formation of iminothiazolines from thioureas and a-halo ketones are readily effected with alumina under microwave irradiation. 

Aminopropylsilyl-tethered mesoporous siUcates such as MCM-41 also catalyze the Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate in toluene solvent [109]. Mesoporous alumina also acted as a base catalyst for the Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate [110]. 

In addition, measurements of the intrinsic reaction rate (free of external and internal diffusion limitations) were achieved by the strict control of the thickness of SIM shell on SIM/alumina beads. The Hnearity observed between the variation of the MOF layer thickness and the conversion observed for the Knoevenagel condensation demonstrated that the reaction takes place inside the whole MOF layer through the porosity and not just at the external surface. 

Malononitrile reacts with acetone in water in the presence of KF-alumina to give 2-aza[2.2.2]octane in high yield via Knoevenagel condensation followed by double cyclization [15]. The bicyclo adduct heated directly or refluxed in tetralin releases 2-methylpropene (retro Diels-Alder reaction), giving the corresponding pyridine derivative. 

Numerous types of basic heterogeneous catalysts, such as alkahne earth metal oxide, anion exchange resins and alkali metal compounds supported on alumina or zeolite can catalyze various chemical reactions such as isomerization, aldol, Michael, and Knoevenagel condensation, oxidation and transesterification [1], Today considerable attention is devoted to the production of biodiesel (FAMEs) as an alternative for petroleum-derived diesel fuel. Biodiesel is synthesized by direct transesterification of vegetable oil or animal fat with a short-chain alcohol, viz. methanol, ethanol, and isopropanol in presence of an acid, base or enzymatic catalyst [2], Considering the advantages of solid base catalysts, for easy separation and recovery, reduced corrosion and environmental acceptance [1], many studies have been conducted on basic heterogeneous catalysts development for biodiesel production [3-13],... 

Shindalkar et al. (2006) developed an ecofiiendly and rapid methodology for Knoevenagel condensation of 4-oxo-(4H)-l-benzopyran-3-carbaldehyde with Mel-drum s acid using acidic alumina under solvent-free microwave irradiation in excellent yield (90-95%). 

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