A-Keto-/?-dicarboxylic acid esters

Oxalacetic acid esters s. a-Keto-/ -dicarboxylic acid esters... 

Oxalacetic acid esters s. a-Keto-/ -dicarboxylic acid esters Oxalic acid as reagent 16, 253 18, 231, 332, 604... 

Dieckmann Condensation The intramolecular equivalent of a Claisen condensation where dicarboxylic acid ester undergoes base-catalyzed cyclization to form a P-keto ester. 

We saw in Section 19.1 that it is harder to remove a proton from an a-carbon if the electrons are delocalized onto the carbonyl group of an ester rather than onto the carbonyl group of a ketone. For the same reason, a higher temperature is required to decarboxyiate a 8-dicarboxylic acid such as malonic acid than to decarboxyiate a jS-keto acid. 

The Knorr pyrrole synthesis was also employed for the synthesis of 3-trifluoropyrroles [91]. Treatment of ethyl trifluoroacetoacetate 267 with sodium nitrite in acetic acid led to the oxime 268. Refluxing with zinc dust and addition of 1,3-dicarbonyl compounds 269 afforded the 3-trifluoromethylpyrroles 270 in moderate yields. Using more acidic trifluoroacetic acid allowed to lower the reaction temperature to 70 °C [92]. Using a similar approach, the tricarboxylic acid ester 273 was prepared starting from the acetone dicarboxylic acid ester 271 and the fluorinated keto ester 272 [93]. 

Keto-a-dicarboxylic acid esters s. Acylmalonic acid esters, a-Halogeno-/5-keto-a-dicarboxylic acid esters a-Ketoenollactones 16, 328 Ketoisocyanates... 

This reaction consists of the condensation of two molecular equivalents of a 1,3 diketone (or a J3-keto-ester) with one equivalent of an aldehyde and one of ammonia. Thus the interaction of ethyl acetoacetate and acetaldehyde and ammonia affords the 1,4-dihy dro-pyridine derivative (1), which when boiled with dilute nitric acid readily undergoes dehydrogenation and aromatisation" to gb e the diethyl ester of collidine (or 2,4,6-trimethyl-pyridine-3,5 dicarboxylic acid (II)). For the initial condensation the solid aldehyde-ammonia can conveniently be used in place of the separate reagents. 

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