Carboxylic acid derivatives transesterification

The cinnamyl ester can be prepared from an activated carboxylic acid derivative and cinnamyl alcohol or by transesterification with cinnamyl alcohol in the presence of the H-Beta Zeolite (toluene, reflux, 8 h, 59-96% yield). It is cleaved under nearly neutral conditions [Hg(OAc)2, MeOH, 23°, 2-A h KSCN, H2O, 23°, 12-16 h, 90% yield]or by treatment with Sulfated-Sn02, toluene, anisole, reflux. The latter conditions also cleave crotyl and prenyl esters. 

Transesterification and Hydrolysis of Carboxylic Acid Derivatives, Alcohols, and Epoxides... 

Problem-Solving Strategy Proposing Reaction Mechanisms 1007 Mechanism 21-8 Transesterification 1008 21-7 Hydrolysis of Carboxylic Acid Derivatives 1009 Mechanism 21-9 Saponification of an Ester 1010 Mechanism 21-10 Basic Hydrolysis of an Amide 1012 Mechanism 21-11 Acidic Hydrolysis of an Amide 1012 Mechanism 21-12 Base-Catalyzed Hydrolysis of a Nitrile 1014 21-8 Reduction of Acid Derivatives 1014... 

Hydroxide ion promotes only hydrolysis reactions, not transesterification reactions or aminolysis reactions. Hydroxide ion cannot promote reactions of carboxylic acid derivatives with alcohols or with amines because one function of hydroxide ion is to provide a strong nucleophile for the first step of the reaction. Thus, when the nucleophile is supposed to be an alcohol or an amine, nucleophilic attack by hydroxide ion would form a product different from the product that would be formed from nucleophilic attack by an alcohol or amine. Hydroxide can be used to promote a hydrolysis reaction because the same product is formed, regardless of whether the attacking nucleophile is H2O or HO . 

Subsequently it was found140 that ethyl 2-alkyl-1//-azepine-1-carboxylates can be isolated from a mixture of isomeric 1//-azepines by stirring the mixture with potassium hydroxide in ethanol at room temperature. Apparently, this method, which is limited to 2-alkylated azepines, depends on the slower rate of hydrolysis (and subsequent decomposition of the resulting 1H-azepine-l-carboxylic acid) of the sterically hindered 1-(ethoxycarbonyl) group. Although the yields of l//-azepines are poor (4-7%, vide supra), the method provides access to otherwise difficult to obtain, isomerically pure 2-alkyl-1//-azepines. Under the basic hydrolysis conditions aryl 2-alkyl-l//-azepine-1-carboxylates undergo transesterification to the l-(ethoxycarbonyl) derivatives. 

The method published by Pfizer5 relies on the formation of an ester 21 of an intermediate carboxylic acid 19 with the alcohol 20 derived from available mandelic acid and the separation of the diastereoisomers by chromatography rather than crystallisation. We can assume that the classical crystallisation of diastereoisomeric salts was not successful. Removal of the ester was simplified as a transesterification. CDI is carbonyl-di-imidazole. 

Pyrrole-based anthranilic acid derivatives have been prepared utilizing a four step sequence starting from arylacetonitriles 4 <04T2267>. Condensation of the latter with ethyl formate followed by treatment with diethylaminomalonate hydrochloride (DEAM-HCl) led to enamine 6. Cyclization and transesterification then gave 3-aminopyrrole-2-carboxylate 7. The acid-mediated cyclocondensation of methylaminoacetaldehyde dimethyl acetal with malonitrile provided a novel synthesis of 2-amino-3-cyanopyrroles, useful building blocks for the preparation ofpyrrolo[2,3- f]pyrimidines <04OL2857>. 

The resin of E.foliosissima contained three carboxylic acids as the major metabolites which could be isolated more conveniently as their methyl ester derivatives. The major component was the unstable acetoxy ester (111) which displayed an allylic tertiary alcohol. Transesterification of the acetate with NaOMe, followed by heating the derived hydroxy compound in a solution of CDCI3, led to the formation of the tetrahydropyran (112). This compound proved identical to the second major metabolite isolated from the methylated acidic fraction. This interrelationship was fortunate... 

Three novel triterpenoid saponins with hypoglucaemic activity, isolated from a Colombian climbing plant and named tuberosides A, B, and C, contain P-d-glucopyranose esterified at the anomeric centre with oleanic acid derivatives. Porphyrine-carboxylate esters of D-galactopyranose have been synthesized either by transesterification of a porphyrine methyl ester with l,2 3,4-di-0-iso-propylidene-a-D-galactopyranose, followed by acetal hydrolysis or by condensation of 6-0-(4-formylbenzoyl)-D-galactose (37) with pyrrole. ... 

The transesterification reaction is a useful transformation that converts esters to other esters upon reaction with alcohols, as a result of exchange of alkoxy groups, avoiding the use of air- and moisture-sensitive reagents, such as acid chlorides. Further, ester-to-ester transformation is particularly useful when the carboxylic acid and their activated derivatives are not readily available [44]. In general, transesterification of secondary alcohols is slower than that of primary alcohols. The reaction is not atom-economical, as it produces, in addition to the desired ester, an equivalent of alcohol. Circumventing this undesired path, we have devised a novel method for transesterification in which dihydrogen is formed as the only byproduct, rather than alcohols, upon reaction of symmetrical esters with secondary alcohols. 

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