Acetonitrile, carboxylic group activation

Reaction with Hydroxy Acids. A study of reactions of threo-3-hydroxycarboxylic acids (15) with DEAD and TPP revealed that both hydroxyl group activation (HGA) and carboxyl group activation processes (CGA) are involved. With small R and R, the zwitterion (16) is more stable than (17), so that HGA is exclusively observed, resulting in the formation of alkenes. On the other hand, the CGA process via (17) is progressively preferred as the size of R and increases (eq 16). When the reaction is carried out in acetonitrile, CGA predominates. ... 

Macrolactonization. The usually difficult lactonization to ll-membcred pyrroli-zidine dilactones can be achieved by use of a trimethylsilylethyl ester (8, 510-511) and activation of the lo-hydroxyl group by mesylation. Thus treatment of 1 with (C4H,)4N F in acetonitrile at 30° liberates the carboxyl group with spontaneous cyclization to the diastereomer 2, the methoxymethyl ether of dZ-crispatine. ... 

Scheme 4. Idealized sketches of gold surfaces for DNA hybridization sensors prepared by (a) chemisorption of thiolated ssDNA capture probes followed by chemisorption of a dilutor alkylthiol [168] and by (b) chemisorption of a mixed alkylthiol SAM followed by covalent attachment of an amino-terminated ssDNA capture probe (surface-bound carboxylic groups are activated by reaction with 0-(N-auccimrmdyl)-N,N,N, N -tetramethyluronium tetrafluoroborate in acetonitrile in the presence of N, A-diisopropylethylamine, [172]).

Amino acids activated at the amino group by a benzotriazolide moiety react with amino acids under elimination of benzotriazole and C02 to give peptides. Reaction is achieved by warming up equimolar amounts of the components in anhydrous acetonitrile or aqueous acetone.[45] The benzotriazolylcarbonylamino acids are prepared from benzo-triazolyl-1-carboxylic acid chloride and amino acids.[46]... 

Route A 1- is very convenient for the substitution of OH groups by bromide or iodide. The reaction conditions are relatively mild (acetonitrile, room temperature, and reflux for 1—3 h, neutral medium). The activating halide (methyl iodide, ally or benzyl bromide) is added in excess (5 equivalents) or in large excess (10 equivalents) when the resultant halide is nearly as reactive as the activating halide. The imidazolium-iV-carboxylates are the important intermediates, which undergo a displacement reaction to give the halides,... 

When the reactions were carried out in chloroform for 2 hr, isopropyli-dene methoxymethylenemalonate reacted on the active methylene group of 2-benzimidazolylacetate and acetonitrile (1666) in the first step, and in the next step, one of the ring nitrogens was involved in a cyclization to give pyrido[l,2-a]benzimidazole-2-carboxylic acids (1667) in 86-89% yields (88YZ856). 

This procedure offers a convenient method for the esterification of carboxylic acids with alcohols2 and thiols2 under mild conditions. Its success depends on the high efficiency of 4-dialkylaminopyridines as nucleophilic catalysts 1n group transfer reactions. The esterification proceeds without the need of a preformed, activated carboxylic acid derivative, at room temperature, under nonacidic, mildly basic conditions. In addition to dichloromethane other aprotic solvents of comparable polarity such as diethyl ether, tetrahydrofuran, and acetonitrile can be used. The reaction can be applied to a wide variety of acids and alcohols, including polyols,2 6 a-hydroxycarboxylic acid esters,7 and even very acid labile... 

In the course of this reaction, a molecule with activated car bon-hydrogen bunds, such as acetonitrile, is both metallaicd and carboxylated at the same time. A similar reaction, the insertion of CO into a mclallatcd phosphine ligand, was found in the thermolysis of U(dinpc) CI CO [53]. and the coordinated carbon dioxide carboxylates one methyl group of the dmpe ligand as shown in Equation (6). 

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