Amidation, boron-catalyzed

The proposed mechanism of the boron-catalyzed amidation is depicted in the Figure. It has been ascertained by H NMR analysis that monoacyloxyboronic add 1 is produced by heating the 2 1 mixture of 4-phenylbutyric add and [3,5-bis(trifluoromethyl)phenyl]boronic acid in toluene under reflux with removal of water. The corresponding diacyloxyboron derivative is not observed at all. When 1 equiv of benzylamine is added to a solution of 1 in toluene, the amidation proceeds even at room temperature, but the reaction stops before 50% conversion because of hydrolysis of 1. These experimental results suggest that the rate-determining step is the generation of 1. 

The reaction of vinyl-substituted silanes and octavinylsilsesquioxane with vinyl-substituted amides, amines (carbazole) as welt as boronates catalyzed by I proceeds effectively to yield under optimum conditions stereo- and/or regio-selectively l-silyl-2-/V- and 1,1-silylboryl-substituted ethenes. 1-silylvinyl carbazole can also be obtained via cross-metathesis of vinylsilane with vinylcarbazole, but only in the presence of the 2nd generation Grubbs catalyst (IV). 

The mechanism that we have proposed to explain boron-catalyzed amidation is depicted in Scheme 1. In general, arylboronic acids contain varying amounts of cyclic trimeric anhydrides (boroxines). The rate-determining step is the generation of 15. 

The hydrolysis of nitriles catalyzed by boron trifluoride is a reliable and high yield process for conversion to the corresponding amide. Other methods give variable yields and may result in a significant quantity of acid being formed, whereas the procedure given below frequently results in yields above 90%. 

The same authors performed a microwave assisted Stille reaction on the Rink amide (RAM) Tentagel polymer-tethered 4-iodobenzoic acid [5 b]. Successful palladium-catalyzed coupling of heteroaryl boronic acid with anchored 4-iodobenzoic acid enabled both >99% conversion of the starting material within 3.8 min (45 W) and a minimal decomposition of the solid support. The coupling reactions were realized in a mixture of polar solvents (H20-EtOH-DME, 2.5 1.5 6). 

TRIFLUOROPHENYL)BORONIC ACID-CATALYZED AMIDE FORMATION FROM CARBOXYLIC ACIDS AND AMINES N-BENZYL-4-PHENYLBUTYRAMIDE [Benzenebutanamide, N-(phenylmethyl)-]... 

To indicate the generality cind scope of 3,4,5-trifluorophenyl)boronic acid-catalyzed amidation, the reaction is examined with various structurally diverse carboxylic acids and... 

EXAMPLES OF AMIDATION CONDENSATION BETWEEN CARBOXYLIC ACIDS AND AMINES CATALYZED BY (3,4,5-TRIFLUOROPHENYL)BORONIC ACID ... 

TRIFLUOROPHENYL)BORONIC ACID-CATALYZED AMIDE FORMATION FROM CARBOXYLIC ACIDS AND AMINES ... 

This four-component reaction represents a straightforward method for the preparation of unsaturated esters and amides [156-159]. The system Pd(OAc)2/SIPr HC1 has been reported to efficiently catalyze the coupling of diazonium salts with boronic acids in the presence of CO and ammonia [160] to yield the corresponding amides in good yields (Scheme 17). 

When carboxylic acids are treated with ammonia or amines, salts are obtained. The salts of ammonia or primary or secondary amines can be pyrolyzed to give amides, but the method is less convenient than 16-72, 16-73, and 16-75 and is seldom of preparative value. Heating in the presence of a base such as hex-amethyldisilazide makes the amide-forming process more efficient. " Boronic acids catalyze the direct conversion of carboxylic acid and amine to amides. 

It is well known that silylation of allyl derivatives with vinylsilane catalyzed by a ruthenium hydride complex is accompanied by isomerization ofpropen-l-yl to propen-2-yl derivatives as well as homo-coupling of vinylsilane when equimolar amounts of the initial substances are used. If catalyst I was used in the SC of allyl amide and allyl amine with vinylsilanes, a S-fold excess of olefin to vinylsilane was used to stop homocoupling of vinylsilane, but simultaneously no more than 5% of isomerization of allyl compound was observed [19, 26]. When allyl boronate is used instead of allylamine under mild conditions (20 - 40 °C), the two reactions catalyzed by I and IV yield stereoselectively -product (see Scheme 4) [26]. 

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