Knoevenagel reaction metal catalyzed

Among the most important reactions in organic synthesis are those that form carbon-carbon bonds. Classically this was accomplished using base-catalyzed reactions such as the aldol, Claisen, and Knoevenagel condensation reactions. Modem versions of these reactoins often display remarkable stereoselectivity.1 Unfortunately, many types of carbon atoms cannot be joined together by these reactions, for example, an aryl carbon to another aryl carbon. It took the development of transition metal-catalyzed reactions before new types of carbon-carbon and carbon-heteroatom bonds could be created. Of particular note in this regard are the reactions catalyzed by palladium, usually in its 0 or +2 oxidation state.2,3,4,5... 

The Knoevenagel reaction is a cross-aldol condensation between an aldehyde and an active methylene compound, which produces water as sole side product (Figure 10.7). This reaction is usually catalyzed by bases in solution or by some sohds such as metal oxides [89]. 

The preparation of the PPV skeleton can be generally classified into two main strategies (i) olefinations methods to prepare the vinylene double bond and (ii) transition-metal-catalyzed single bond formation between the arene and vinylene components. The former includes Wittig-, Wittig-Horner- and Knoevenagel-type condensations, whereas the latter approach was demonstrated via Heck, Stille, Suzuki Miyaura and McMurry coupling reactions (Scheme 7.5). 

Some drawbacks of the precursor routes mentioned above have been overcome by the use of polycondensation- and C-C-bond-coupling reactions. To produce soluble PPV-, poly(thiophene)-, or poly(pyrrol) derivatives for spin coating preparation, various types of transition metal catalyzed reactions, such as the Heck-, Suzuki-, and Sonogashira-reaction, Wittig- and Wittig-Horner-type coupling reactions, or the McMurry- and Knoevenagel-condensation have been utilized. 

Aminosilicas have been widely studied for use in catalysis, either as a base catalyst or as a support for metal complexes (12). For example, amine functionalized silica can be used to catalyze the Knoevenagel condensation, an important C-C bond forming reaction. Also, the amine sites on the silica can be further functionalized to form supported imines, guanidine, and other species... 

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],... 

---