Amines dehydrative condensations with carboxylic acids

PhjSbO mediates the dehydrative condensation of carboxylic acids with amines via Ph3Sb(OCOR)2 as reactive intermediates [146]. This catalytic system has been applied to dipeptide synthesis (Scheme 14.73) [147]. Treatment of olefins with a mixture of AcOH and P4S10 in the presence of Ph jSbO affords alkylthio esters [148]. 

Dehydrative Condensation of Carboxylic Acids with Amines and Alcohols. In the presence of a mercuric catalyst, (1) causes dehydrative condensation of carboxylic acids with H-acidic materials such as amines and alcohols to give the corresponding amides, esters, lactones, and peptides in high yields. ... 

Dehydrative Condensation of Carboxylic Acids with Amines and Alcohols. For reversible fluorescent labeling of amino groups, ethoxy(trimethylsilyl)acetylene was used as a dehydrating reagent to couple dansylaminomethylmaleic acid (DAM) with benzylamine through a maleic anhydride intermediate (eq 6). ... 

Other recent relevant developments have been the replacement of conventional acid catalysts with greener analogues. Direct esterification of carbo Q lic acids and alcohols continues to be a focus of attention. As examples, diphenylammonium triflate 8 and bulky diatylammonium sulfonates were shown to catalyse ester condensation of carboxylic acids and alcohols efficiently, and without the need for azeotropic water removal in the former case. Pentafluorophenylammonium triflate 9 was shown to be an efficient and cost-effective catalyst not only for esterification, but also for thioesterification, transesterification and macrolactone formation without requiring a dehydrating system. The superior catal)4ic efficiency of 9 relative to 8 was ascribed to the lower basicity of the pentafluoroaniline counter amine compared to diphenylamine. In related work, polyaniline... 

Dehydration (cf., 6, 648). A reagent (1), prepared in situ from (C6H5),PO and Tf20 in the molar ratio 2 1, effects dehydration, usually at 25°, of amides or oximes to nitriles in >90% yield. It also effects condensation of acids and amines to form amides. The reaction of an aryl carboxylic acid with an o-phenylenediamine promoted by 1 provides 2-arylbenzimidazoles in >80% yield (equation I). If the... 

Attempts to react enol(ate)s of esters with aliphatic aldehydes are doomed as the aldehyde will simply condense with itself. If the ester is replaced by a malonate 60, there is so much enol(ate) from the (5-dicarbonyl compound that the reaction is good. This style of aldol reaction is often called a Knoevenagel reaction10 and needs only a buffered mixture of amine and carboxylic acid. The enol reacts with the aldehyde 61 in the usual way and enolisation of the product 62 usually means that dehydration occurs under the conditions of the reaction. 

ArsBi bearing ortho methoxy groups mediates dehydrative condensation of a-monosubstituted carboxylic acids with alcohols and amines (Scheme 14.139) [288]. Macrocyclic esters can be synthesized by the ArsBi-templated reaction of diols with dicarboxylic acid derivatives [289]. The Bi-C bonds of Ar Bi are cleaved by diphenyl diselenide and ditelluride to give aryl phenyl selenides and tellurides, respectively (Scheme 14.140) [290]. The reaction of ArsBi with elemental chalcogen (E Se, Te) affords a mixture of the respective dichalcogenides (ArEEAr) and monochalcogenides (ArEAr). 

In these reactions, hydrolysis of diphenyl and triaryl phosphites to monoaryl phosphites and phenol was coupled by dehydration between carboxylic acids and amines or alcohols to the corresponding amides and esters. Therefore, the reaction can be generalized as a hydrolysis-dehydration reaction (Scheme 2). The concept of the hydrolysis-dehydration reaction using phosphites has been drown to be applicable also to reactions with other phosphorus compounds such as phosphinites, phos-phonites and phosphorates s Aryl esters of these phosphorus compounds are effective as condensing agents in the production of carboxylic amides and esters (from carboxylic acids and amines or alcohols, respectively) whereas alkyl esters are ineffective (Eqs. (1-3)) ... 

Plan We discussed substitution reactions (including addition-elimination and dehydration-condensation) and hydrolysis. In (a), a carboxylic acid and an alcohol react, so the reaction must be a substitution to form an ester and water. In (b), an amide reacts with OH, so it is hydrolyzed to an amine and a sodium carboxylate. 

A series of A-formylated aliphatic amino acids 207 were subsequently attached to the Wang resin as shown in Scheme 4.3.1, affording 208. Dehydration of 208 provided resin-bound isocyanides 209 quantitatively as shown by H-NMR of the resin. Multicomponent condensation of resin 209 with arylglyoxals 210, primary amines and carboxylic acids afforded resin-bound a-(N-acyl-N-alkylamino)-P-ketoamides 211 that were further reacted with a large excess of NH4OAC in AcOH to give immobilised imidazoles 212. Final cleavage with 10% TFA provided imidazoles 213. 

Dehydrations using chlorosulfonic acid-pyridine (pyridinium sulfamates) provide a convenient synthetic route to amides without die intermediacy of acyl halides. The carboxylic acid was condensed with the amine in pyridine solution containing chlorosulfonic acid at 0-10 °C to give the amides (Equations 9 and 10).2 ... 

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