Doebner-Knoevenagel reaction

A bifunctional polystyrene bearing both 4-dimethylaminopyridine (DMAP) and piperidine groups was an effective organocatalyst for decarboxylative Doebner-Knoevenagel reactions of arylaldehydes and monoethyl malonate to give F-cinnamates in high yields (Scheme 6.4) [83]. 

A final decarboxylation step is also part of a hydroformylation-decarboxylative Knoevenagel (= Doebner-Knoevenagel) reaction sequence (Scheme 5.144)... 

Scheme 5.144 Hydroformylation-decarboxylative Knoevenagel (Doebner-Knoevenagel) reaction and typical reaction products.

The Doebner condensation (or reaction) is a slight modification of the Knoevenagel reaction and consists in warming a solution of the aldehyde and... 

The term Knoevenagel reaction however is used also for analogous reactions of aldehydes and ketones with various types of CH-acidic methylene compounds. The reaction belongs to a class of carbonyl reactions, that are related to the aldol reaction. The mechanism is formulated by analogy to the latter. The initial step is the deprotonation of the CH-acidic methylene compound 2. Organic bases like amines can be used for this purpose a catalytic amount of amine usually suffices. A common procedure, that uses pyridine as base as well as solvent, together with a catalytic amount of piperidine, is called the Doebner modification of the Knoevenagel reaction. 

When the reactant is of the form ZCH2Z, aldehydes react much better than ketones and few successful reactions with ketones have been reported. However, it is possible to get good yields of alkene from the condensation of diethyl malonate, CH2(COOEt)2, with ketones, as well as with aldehydes, if the reaction is run with TiCU and pyridine in THF. In reactions with ZCH2Z, the catalyst is most often a secondary amine (piperidine is the most common), though many other catalysts have been used. When the catalyst is pyridine (to which piperidine may or may not be added) the reaction is known as the Doebner modification of the Knoevenagel reaction. Alkoxides are also common catalysts. 

When the amine catalyst is specifically pyridine, the reaction is known as the Doebner Modification of the Knoevenagel Reaction ... 

The forward synthetic reaction is a base-catalysed condensation reaction between two carbonyl compounds, the aldol condensation leading to -hydroxy-aldehydes or / -hydroxyketones followed by dehydration. This sequence is one of the most important carbon-carbon bond forming reactions, and aldol-type condensation reactions are considered in a number of other sections of the text, for example, the Doebner reaction (Section 5.18.3, p. 805), the Knoevenagel reaction (Section 5.11.6, p. 681), the Perkin reaction (Section 6.12.3, p. 1036) and the Robinson annelation reaction (Section 7.2). 

Condensation reactions of the aldol type play an important part in heterocyclic chemistry. There are a large number of condensation reactions that are closely related to the aldol condensation. Each of these reactions has its own name Claisen, Dieckmann, Doebner, Knoevenagel, Perkin, to mention a few, but the chemistry is essentially the same as that of the aldol condensation. 

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