Carboxylic esters transesterification

Alcoholysis of Carboxylic Esters. Transesterification Alkoxy-de-alkoxylation... 

The process of transesterification is an important way to prepare a large number of esters from more complex or more simple esters without passing through the carboxylic acid. Transesterification can be used to convert one type of ester to another type that can then be removed under a different set of conditions. This section describes many of the methods that have been found effective for ester metathesis. ... 

Besides allylic substitution reactions it was also shown that [Fe(CO)3(NO)] 76 is catalytically active in transesterification reactions under neutral conditions (Scheme 24) [70]. Various activated acyl donors 97 can be used to give rise to the corresponding carboxylic esters 100 in good to excellent yields. This reaction proceeds in the absence of additional ligands in nonpolar solvents, for example, hexane. Mechanistically, the reaction is assumed to proceed via a Fe-acyl-complex 98 (Scheme 24). 

Scheme 2 A proposed mechanism for Lal+ ( OCH3)2 catalyzed transesterification of carboxylate esters with good and poor leaving groups.

Transesterifications, of neutral carboxylate and organophosphate esters with transition metal ion and Ln3+ catalysts, 284-288 alcoholysis of carboxylate esters, 288-294 alcoholysis of neutral phosphate esters, 294-308... 

The biotechnological synthesis of lactones has reached a high standard. Besides microbial production, lactones can also be enzymatically produced. For instance, a lipase-catalysed intramolecular transesterification of 4-hydroxy-carboxylic esters leads enantioselectively (ee>80%) to (S)-y-lactones the chain length may vary from C5 to Cl 1 [13]. y-Butyrolactone can be produced in that way with lipase from Mucor miehei [30]. 

Hydrolysis of carboxylic esters 0-17 Transetherification 0-18 Payne rearrangement 0-23 Transesterification 0-55 Ammonolysis of carboxylic esters 0-68 Cleavage of ethers with concentrated acids... 

Naturally, less scope is available with the ester component and the C-2 substituent in the chromone is commonly alkyl or ethoxycarbonyl, or is absent. The use of diethyl oxalate offers an added attraction the intermediate 1,3-diketo ester (436) readily undergoes transesterification, thereby allowing the synthesis of various chromone-2-carboxylic esters to be achieved from the one starting material (Scheme 148) (74JCS(P1)2570). 

Alternative reactions employ coupling reagents such as DCC (Steglich Esterification), preformed esters (transesterification), carboxylic acid chlorides or anhydrides. These reactions avoid the production of water. Another pathway for the production of esters is the formation of a carboxylate anion, which then reacts as a nucleophile with an electrophile (similar reactions can be found here). Esters may also be produced by oxidations, namely by the Baeyer-Villiger oxidation and oxidative esterifications. 

The hydroboration of acetylenes (3) with diisopinocampheylborane (IpC)2BH in THF led after refunctionalisation and transesterification to the olefins (4a, b, c) isolated in good yields. Monooxidation with mCpBA led to the sulfoxide (4d) whereas the sulfone (4e) was obtained with two equivalents of mCpBA. The same sulfone (4e) could also be obtained in an excellent overall yield by radical addition of phenylsulfonyl iodide to the pinacol ester of vinylboronic acid followed by a dehydroiodination in the presence of Et2N (87 % overall yield). The carboxylic ester (4a) could be transformed into the corresponding carboxylic acid (4f) (79 % yield) 11 which led to the acid chloride (4g) by treatment with freshly distilled thionyl chloride at 0°C (91 % yield), p-keto vinylboronates are easily accessible by oxidation of the corresponding protected allylic alcohol according to the following scheme ... 

Transesterification reactions of carboxylic esters or conversion into the amides is promoted by a stoichiometric amount of BBra [34],... 

Acylation of a simple thiol with an alkyl carboxylate is not a very suitable method for preparation of S-alkyl thiocarboxylates. Transesterification is, however, possible if either the thiol or the carboxylic ester is activated. The enhanced reactivity of boron, aluminum and silicon thiolates has been utilized for the synthesis of a large variety of thiocarboxylic S-esters, including hydroxy derivatives (from lactones). a,P-Unsaturated thiol esters, e.g. cinnamoyl or 2-butenoyl derivatives, are also accessible. Michael addition, an undesirable side reaction of thiols, is completely avoided if alkyl trimethylsilyl sulfides ortris(arylthio)boranes are applied. ... 

Transesterification. The transesterification of carboxylic esters with primary and secondary alcohols is readily achieved with BuSn(=0)OH as catalyst (e.g., in refluxing toluene). Functional groups such as acetals, double and triple bonds, iV-protecting groups commonly employed in peptide synthesis, and P-lactam ring are not affected. 

It has been disclosed that 1,3-disubstituted tetraalkyldistannoxanes are extremely effective catalysts for transesterifications of carboxylic esters in which secondary... 

Several reports show that it is possible to carry out a transesterification selectively at the carboxylic ester moiety of dialkyl l-(alkoxycarbonyl)methyIphosphonates rather than at the phosphonic ester moiety with primary and secondary alcohols in the presence of NaH or DMAPP For example, a number of chiral phosphonates have been prepared in high yields (80-96%) by DMAP-catalyzed transesterification of dialkyl l-(alkoxycarbonyl)methylphospho-nates with 8-phenytmenthol in toluene at reflux." " -" ... 

Without additional reagents /3-Diethylaminoethyl esters of thiazole carboxylic acids Transesterification... 

Carboxylic esters cannot be brominated by elemental bromine. However, mixtures of esters and acid chlorides in molar proportions 1 1 to 5 1 can be brominated, yields being the same as from 2-6 moles of acid chloride 562 here the 2-bromo fatty acid chloride, formed as intermediate, reacts with the fatty acid ester in a transesterification that leads to the oc-bromo ester and the un-brominated chloride. 

This method is always successful in replacing one primary alcohol residue by another or by the residue of a secondary alcohol of higher boiling point, but it cannot be used for preparation of esters of tertiary alcohols. Esters of tertiary alcohols can be prepared by Verley s method,865 namely, mutual transesterification of two carboxylic esters ... 

In a mixture of SBO, methanol, and water, a lipase can carry out the transesterification reaction at high yields. The end product is similar to methyl soyate, except for the added aza-carboxylate ester. Since methanol is in excess, dimethyl esters are formed. The reaction can be conducted at a low temperature (35°C). Several lipases have been attempted, and the reaction is relatively straightforward. The use of an immobilized lipase (e.g., Novozym 435) is particularly beneficial because it allows enzyme recycling and cost reduction. 

In contrast to the carboxylic esters, no transesterification or desulfonation (cleavage of the C-S bond) is observed, in the alkyl nitration of alkyl sulfonate esters. Ethyl butanesulfonate is converted to ethyl a-nitrobutanesulfonate (54%) and the potassium salt of o-nitrobutanesulfonic acid (11%), about 33% of the ester being recovered (eq 15). The salt of a -nitrobutanesulfonic acid arises from a B-elimination with the loss of ethylene (13). 

Transesterification. lAlkoxy-de-alkoxylation or Alcoholysis of carboxylic esters] It is catalyzed by acids or bases. It is an equilibrium reaction and should be shifted in the desired direction. 

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 actinides and lanthanides or f-block metal alkoxides are the last group. According to the report of Nawaratna and co-workers, yttrium isopro-poxide has been catalyzed transesterification reaction of fatty acids (reaction 7.13) [78]. Hatano et al. have used this strategy in the presence of lanthanum alkoxides for transestrification of carboxylic esters and preparation of new esters [79]. 

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