Doebner condensation

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

Higher-molecular-weight normal 2-alkenoic acids have been prepared in poor yields by the Doebner condensation of aldehydes with malonic acid,5-7 and by the Reformatsky reaction of aldehydes with ethyl bromoacetate followed by dehydration.8 The a-iodo acid, prepared from the bromo acid, has been dehydrohalogenated with potassium hydroxide in ethanol,9 but large quantities of the a-hydroxy acid are formed as a by-product which is difficult to separate in some instances. The present procedure is an adaptation of a published method.6... 

The Doebner condensation uses malonic acid, malonic acid monoesters, or cyanoacetic acid instead of the coiTesponding dialkyl malonates. Usually the product stereoisomer with the carboxyl group trans to the larger substituent predominates. 

Jacobson s synthesis of pellitorine, 5, (Scheme 1) [20] is based on two sequential Knoevenagel-Doebner condensations, and gives the desired product in a modest overall yield of 3.3%. 

Knoevenagel condensation is also known as Doebner Condensation . 

When malonic acid is used as the enolate partner, with pyridine as the base, the condensation reaction with aldehydes is known as the Doebner condensation. This is an important route to non-a-amino acids. An example of this condensation when... 

An earlier version of this reaction condensed 4.18 and malonic acid to give 4.19. Refluxing 4.19 led to the monomer 4.20), which decarboxylated under the reaction conditions to give 3-amino-3-phenylpropanoic acid, 4.21. Doebner condensation with malonic acid itself sometimes leads to very poor yields of product, as seen above. An improvement in the reaction used nitro-ester 4.22 rather than malonic acid, and 4.23 [ethyl 3-(N-phenylamino)-2-nitroprop-2E-enoate] was produced in good yield. 

Knoevenagel-Doebner condensations of 2,4- -ethylidene-D-erythrose and -D-threose with malonlc acid or its mono-methyl ester furnishes... 

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