Pyridine-3,5-dicarboxylic acid, reaction complexes

Reaction of the m-nitrophenyl ester of pyridine-2,5-dicarboxylic acid with cyclodextrin (see Section 3) gives a picolinate ester [52] of a cyclodextrin secondary hydroxyl group (Breslow, 1971 Breslow and Overman, 1970) which will bind metal ions or a metal ion-pyridine carboxaldoxime complex. Such a complex will catalyse hydrolysis of p-nitrophenyl acetate bound within the cyclodextrin cavity leading to a rate constant approximately 2000-fold greater at... 

Phenolic esters are obtained similarly. The presence of a nitro group in the aromatic nucleus and the use of pyridine as solvent facilitates the reaction. This reaction is recommended for the characterization of phenols. 2,4,5-Trichlorophenyl-, pentachlorophenyl-, 4-nitrophenyl- and thiophenyl esters of N-acylamino acids are prepared in this manner. These aromatic esters are used in the stepwise lengthening of peptides, du Vigneaud and coworkers synthesized lysine vasopressin from a nonapeptide which they prepared stepwise using the nitrophenyl ester method. Room temperature esterification of dicarboxylic acids and diphenols are also carbodiimide mediated using the 1 1 complex derived from DMAP and p-toluenesulfonic acid as catalyst Methacrylic acid is also esterified with phenols using carbodiimides and DMPA to mediate the reaction. ... 

Olefin-containing esters of pyridine-3,5-dicarboxylic acid are able to form macrocycles using a ring-closing metathesis reaction if the pyridine was protected with complexing Pt. The method was applied to 69- and 75-membered macrocycles <03ZOR449>. An example of a 17-membered ring formation is shown below. 

Pybox L8 (Fig. 4) was synthesized from pyridine-2,6-dicarboxylic acid and optically active amino alcohols via an amido chloride intermediate [ 16,23 ] or via BFj-catalyzed cychzation of intermediate amino alcohols [24]. The combination of Pybox-i-Pr (L8a) and [Rh(COD)Cl]2 (Rl) exhibited catalytic activity as an in-situ catalyst for the reduction of acetophenone (Kl) to give 76% ee (S) [16].However, the complex RhCl3(Pybox-z-Pr) R4a under assistance with AgBF4 accelerated the reduction in THF to give 94-95% ees [23]. Diphenylsilane (SI) was also the best silane in this system. Most aromatic methyl ketones were reduced in 90-99% ees, and reactions of levurinate KIO and 2-octanone Kl 1 resulted in 95% ee and in 63% ee, respectively. The Pybox-Rh catalyst R4a reduced selectively 2-phenylcyclohexanone K12 to give the S-alcohols for both trans- and cis-isomers PI and P2 in 96-99% ees [25]. The catalyst R4a can differentiate only the enan-... 

Similar to the iron chemistry (compare Chapter 2.3), also nickel complexes allow the reaction of one molecule of butadiene with two molecules of CO2 yielding a,u-dicarboxylic acids [48]. In the reaction of butadiene and CO2 in the presence of nickelbis(cyclooctadiene) and tetramethylethylenediamine first a nickelamonocarboxylate is formed (Figure 19). By further treatment with carbon dioxide and by addition of pyridine a nickeladicarboxylate complex is obtained in yields up to 72 %. Decomposition of the complex with methanol/hydrochloric acid gives cis-dimethyl-3-hexenedioate. 

Reaction of chromium(ii) with pyridine-2,4-dicarboxylic acid yields two radical complexes of Cr, one of which is active in reducing cobalt(iii) complexes, the other not. The inactive form is formed in reversible equilibrium, and is believed to be the chelate (30), with apparent formation constant A app = /sT/[H+]x 50 at 20 °C in I.2M-HCIO4. The active form, possibly (31), is not detected as such, but is an intermediate postulated in the reaction [Co(NH3)spy] + + Cr +, when accelerated by the presence of the organic acid. ... 

Many combinatorial libraries are not as easily described as that in Subsection 5.3.1. Often the reactants belong to various classes of compounds and react with each other via complex mechanisms. As an example, consider Ugi s seven component reaction [310]. The reactants are a central building block, pyridine-2,6-dicarboxylic acid... 

Such acid-base reactions take place at the carboxylic groups of suitable ligands such as L-L = 2,2 -bipyridine-4,4 -dicarboxylic acid. e.g. [Ru(bipy)2(L-L)]2+ [131]. In acidic D2O solutions of the Ru(II)-complex [Ru (NH3)5(pyridine)]2+ a light-induced H/D exchange occurs at the pyridine ligand [10,132]. This reaction is also attributed to the enhanced basicity of the coordinated pyridine in the MLCT excited state. 

The autocatalytic behavior may be suppressed by addition of large concentrations of Eu or the latter being the more effective inhibitor. In the case of pyridine ligands with 2,3-, 2,4-, or 2,6-dicarboxylic acids, strongly absorbing complexes are observed in reaction with V(II). 

The catalytic effect of nickel(n) on hydrolysis rates of the salicyl and phenyl esters of pyridine-2,6-dicarboxylic acid is ascribed to the intermediacy of a 1 1 complex between the ester and the nickel(n). Rates of hydrolysis and of reaction with hydroxide are reported.Kinetic and equilibrium studies have... 

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