Carboxylic as reagents

DiphenyI-3-ethylpentane, 48, 82 Diphenyliodonium-2-carboxylate, as reagent for generation of benzyne,... 

A complementary method is the Kochi reaction. This reaction is especially useful for the generation of secondary and tertiary alkyl chlorides through decarboxylation of carboxylic acids, where the classical method may not work. As reagents, lead tetraacetate and lithium chloride are then employed ... 

Besides simple alkyl-substituted sulfoxides, (a-chloroalkyl)sulfoxides have been used as reagents for diastereoselective addition reactions. Thus, a synthesis of enantiomerically pure 2-hydroxy carboxylates is based on the addition of (-)-l-[(l-chlorobutyl)sulfinyl]-4-methyl-benzene (10) to aldehydes433. The sulfoxide, optically pure with respect to the sulfoxide chirality but a mixture of diastereomers with respect to the a-sulfinyl carbon, can be readily deprotonated at — 55 °C. Subsequent addition to aldehydes afforded a mixture of the diastereomers 11A and 11B. Although the diastereoselectivity of the addition reaction is very low, the diastereomers are easily separated by flash chromatography. Thermal elimination of the sulfinyl group in refluxing xylene cleanly afforded the vinyl chlorides 12 A/12B in high chemical yield as a mixture of E- and Z-isomers. After ozonolysis in ethanol, followed by reductive workup, enantiomerically pure ethyl a-hydroxycarboxylates were obtained. 

Formic acid as reagent for carboxylation of 1-methylcyclohexyl cation to form 1-methylcyclohexanecar-boxylic acid, 46, 72... 

In the presence of a [RuCl2(PPh3)3] catalyst N-methylmorphoHne-N-oxide (MMO) reacts with alcohols in dichloroethane or 1,2-dichloroethylene to afford mostly aldehydes together with carboxylic acids. Instead of the rather expensive MMO as reagent, a combination of N-methylmorphoHne and aqueous H2O2 (35 w%) could be used with similar results for the oxidation of long chain alcohols (1-octanol to 1-hexadecanol) [16]. At the end of the reaction the aqueous phase, containing the mthenium catalyst and methylmorphoHne could be recycled with no apparent loss of activity. 

The first step is formation of a pyrrole ring system from two identical aminoketones. It is actually a Knorr pyrrole synthesis, but we do not need to identify it as such, just approach it logically. In fact, if we look back at the Knorr pyrrole synthesis, we shall see that, under chemical conditions, the reagents used here are not sufficiently reactive for the pyrrole synthesis we need a more activated compound, like ethyl acetoacetate. Furthermore, we could not possibly proceed without masking the carboxyls as esters. This underlines how a biosynthetic sequence might differ somewhat from a purely chemical synthesis. 

Nickel(lll) oxide, prepared from a nickel(ii) salt and sodium hypochlorite, is used for the oxidation of alkanols in aqueous alkali [46]. Residual nickel(Ii) oxide can be re-activated by reaction with sodium hypochlorite. Nickel oxides have also long been used in the manufacture of the positive pole in the Edison nickel-iron rechargeable battery, now largely superseded by die lead-acid accumulator, and in the Jungner nickel-cadmium batteries used as button cells for calculators [47]. Here, prepared nickel oxide is pressed into a holding plate of perforated nickel. Such prepared plates of nickel(lli) oxide have been proposed as reagent for the oxidation, in alkaline solution, of secondary alcohols to ketones and primary alcohols to carboxylic acids [48]. Used plates can be regenerated by anodic oxidation. 

Alternatively, oxazolones have been used as reagents to activate and to couple N-protected dicarboxylic amino acids wherein the carboxylate moiety acts as the nucleophile. For example, 2,4-dimethyl-5(4//)-oxazolone 255 reacts with N-benzyloxycarbonyl-L-aspartic acid to give a mixture of the anhydrides 256 and 257. Subsequent reaction of 256 and 257 with phenylalanine methyl ester hydrochloride and A-methylmorpholine produces a mixture of the a-isomer 258 and p-isomer 259 of Al-benzyloxycarbonyl-aspartylphenylalanine methyl ester (Scheme 7.83). °... 

There are very few strong acids in water, and Table J.l lists all the common ones. They include three acids that are often found as reagents in laboratories—hydrochloric acid, nitric acid, and sulfuric acid (with respect to the loss of one proton). Most acids are weak in water. All carboxylic acids are weak in water. 

Among the important reagents for which preparative procedures are given are 2,2 -bipyridine (by nickel directed and catalyzed dehydrogenation of pyridine p. 5), formamidine acetate (p. 39), phenyltrichloromethylmercury (p. 98), and trimethyl- and triethyloxonium fluoroborate (pp. 120, 113). The preparation of palladium catalyst ( Lindlar ) for the selective reduction of acetylenes is described (p. 89), as is the use of di-phenyliodonium-2-carboxylate, as a precursor of benzyne in the synthesis of 1,2,3,4-tetraphenylnaphthalene (p. 107). 

This procedure is illustrative of a general method for preparing a wide range of pure 3,5-disubstituted-4-isoxazole-carboxylic esters and (by hydrolysis) their acids,2 free from positional isomers. A wide range of both primary nitro compounds and of enamino esters can be used,2,3 and the esters thus obtained may then be used as reagents in the isoxazole annela-tion reaction.3,4 The only other general synthesis of these compounds involves chloromethylation and oxidation of a suitable 4-unsubstituted isoxazole.5 This procedure suffers from two difficulties low yields and the unavailability of starting isoxazole. Most methods of isoxazole formation yield a... 

Aldimines can be trifluoromethylated at the imine carbon using Me3SiCF3 in dimethyl formamide at —20 °C, using a lithium carboxylate as catalyst.71 It is proposed that the carbon-silicon bond of the reagent is activated via formation of a lithium silicate bearing carboxylate and DMF ligands on silicon. A similar process has been used for diastereoselective addition to sulftnylimims.12... 

Used to introduce chromophores into carboxylic acids reagent is prepared from 1-naphthaldehyde hydrazone by oxidation with Hg(ll) oxide, with diethyl ether as a solvent acetic acid will destroy excess reagent Reference 30... 

There are several types of chiral derivatizing reagents commonly used depending on the functional group involved. For amines, the formation of an amide from reaction with an acyl halide [147,148], chloroformate reaction to form a carbamate [149], and reaction with isocyanate to form the corresponding urea are common reactions [150]. Carboxyl groups can be effectively esterified with chiral alcohols [151-153]. Isocynates have been used as reagents for enantiomer separation of amino acids, iV-methylamino acids, and 3-hydroxy acids [154]. In addition to the above-mentioned reactions, many others have been used in the formation of derivatives for use on a variety of packed and capillary columns. For a more comprehensive list, refer to References 155-159. 

Diorgano tellurium dicarboxylates were prepared from dialkyl and diaryl tellurium derivatives. Aliphatic carboxylic acids, aromatic carboxylic acids, their sodium or silver salts, and carboxylic acid anhydrides were used as reagents. Dicarboxylic acids such as succinic acid and phthalic acid were reported to give monomeric carboxylates when... 

---