B-ketoesters

The reaction is usually carried out in acid solution, but may also be base catalysed. This is the condensation between aldehydes, ammonia or a primary or secondary amine and a compound containing at least one active hydrogen atom e.g., ketones, b-ketoesters, b-cyanoesters, nitroalkanes, alkynes with C°H). For example. 

By its characteristic carbonyl IR absorption band the product of intramolecular termination, i. e. the cyclic B-ketoester was detected by Goode et al. (58), Glusker et al. (59), and Owens et al. (6o) as one of the products of the oligomerization of MMA with phenylmagnesium bromide or fluorenyllithium in toluene. The same compound was found by Lochman et al. (61) when using metalated methylisobutyrate as the initiator in a THF/pentane mixture at high initiator/monomer ratios. 

The retro-acylation reactions of B-ketoaldehydes (388, X=H), B-diketones (388, X=alkyl) and the retro-Claisen reaction of B-ketoesters (388, X=0R) occur through the formation of an intermediate 389 which gives an ester 390 and the enolate ion 391. Protonation of 391 then gives the corresponding aldehyde (392, X=H), ketone (392, X=alkyl) or ester (392, X=0R). 

Adenosine 5 -(tr1hydrogen diphosphate), 5 5 ester with 3-(ami nocarbonyl)-alcohol dehydrogenase, 63, 17 Adogen 464 [50934-77-5], 60, 11 Alanine, L-, N-carboxybenzyl ester, 63, 182 ALANINE, PHENYL-, N-tert-BUTOXYCARBONYL-, L-, 63, 160 Alanine, N-[(phenylmethoxy)carbonylL- [1142-20-7], 63, 182 Alcohols, alkynyl-, synthesis of, 63, 61 Alcohols, amino-, by reduction of acids, 63, 138 Aldol condensation, intramolecular, asymmetric, 63, 26, 37 Aldol condensation, diastereoselectlve, 63, 94, 104 ALIPHATIC B-KETOESTERS, 61, 5 Alkene photodimerization, 62, 125... 

The retro-ene reaction cleaves an unsaturated compound into two unsaturated fragments. A common example of a retro-ene reaction in organic synthesis is the acid-catalyzed decarboxylation of a (B-ketoester. The ester is hydrolyzed to the (3-ketoacid by the aqueous acid, which rapidly loses carbon dioxide to form enol. The loss of CO2 drives the reaction to the right-hand side. The enol rapidly tautomerizes to the methyl ketone (Scheme 8.17). 

Sum, F.W., and Weiler, L. (1979). Stereoselective synthesis of b-substituted a, b-unsatu-rated esters by dialkylcuprate coupling to the enol phosphate of b-ketoesters. Can J Chem 57 1431-1441. 

This loses one of the carboxylates on heating in the presence of toluene-sulfonic acid to afford the (B-ketoester (82). Reaction of this intermediate with ethylorthoformate then adds a carbon atom to the activated methylene. Heating that compound with cyclopropylamine in effect exchanges the ethoxy group with the amine to afford enamine (84). Treatment 84 with sodium fluoride leads to displacement of one of the ring fluoro groups by the basic nitrogen on the side chain. This step concludes the formation... 

Three different pyridine syntheses starting from polymer-bound enones have been reported. The first synthesis starts from 2-alkylidene- or 2-arylidene-B-ketoesters immobilized on Wang or Sasrin resin (Fig. 6.21). These substrates reacted with enaminones in a Hantzsch reaction to 1,4-dihydropyridines which could be oxidized to the corresponding pyridines with ceric ammonium nitrate (CAN). Cleavage was performed with TFA/DCM. Sixteen compounds were synthesized, with HPLC purities of between 70% and 99%. 

In a solution of an alkoxide salt, the B-ketoester (produced by the Claisen condensation) will give up a hydrogen from the carbon between the two carbonyl carbons. This results in a highly resonance stabilized anion. Using ethyl acetoacetate, we can show how this anion is formed and stabilized ... 

This anion will not be produced from a B-ketoester that has no hydrogens on the carbon between the two carbonyl groups. Such B-ketoesters would result from the Claisen condensation of an ester having only one a hydrogen. Since our problem uses ethyl acetate, the B ketoester anion is formed. This anion, like the enolate anion, is nucleophilic enough to attack the partially positively charged carbonyl carbon of an ester. Here, 0-acylation is much less thermodynamically stable than is C-acylation. Hence, the reaction of the B-ketoester anion with the ester (using ethyl acetoacetate and ethyl acetate as in our problem) is ... 

The product of this reaction accounts for a small portion of the Claisen condensation products. This is because the B-ketoester anion is less nucleophilic than the enolate anion, and will therefore not attack an ester as fast as the enolate anion will. Another reason that the rate of reaction of B-ketoester anion with ester is very slow is due to the steric hindrance the B-ketoester anion is a large group. 

J. Kassanyi, J. Perales, A. Laachach, I. Kawenoki and J.P. Morizur. Preparation of w-Formylalkenoates from cyclic B-Ketoesters, Synthesis 1979, 279-281. 

Yudha, S., Kuninobu, Y, Takai, K. (2008). Rhenium-catalyzed synthesis of stereodefined cyclopentenes from b-ketoesters and aliphatic allenes. Angewandte Chemie International Edition, 47, 9318-9321. 

Base-catalyzed transformation of allylic alcohol and B-ketoester to Y" via anion-assisted Claisen reaction. 

Diels-Alder addition with the silyl ether of buta-1,3-dien-l-ol in the presence of DDQ to yield the fused-phenol derivative (51), which was further modified by standard reactions.A bicyclosugar derivative (52) arises by Dieckmann cyclization of the branched-chain sugar diester (53) in the presence of 18-crown-6, the enolized form of the isomeric B-ketoester (54) is the only product, obtained in low yield (Scheme 11). 8... 

Long chain aliphatic IB-diketones ind alkan-2-ol esters are common constituents of plant surface lipids. The B-dicarbonyl pattern, two carbonyl groups 1,3 one another, has suggested that the biosynthesis of I3-diketones involves condensation of propriate B-ketoesters and esters, via a biological Claisen reaction qihao... 

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