Directivity carboxylate

Perfluoroalkyl iodides can be directly carboxylated with zinc and carbon dioxide under ultrasonic conditions [39] (equation 45) or by the reaction of perfluoroalkyl iodides with carbon dioxide with a zinc-copper couple in DMSO [57] (equation 46) Alkylation of the intermediate carboxylate gives the corresponding ester [52]... 

In the presence of strong acid, formic acid decomposes to water and carbon monoxide. In the process, reactive intermediates form which are capable of direct carboxylation of carbonium ions. Since many carbonium ions are readily generated by the reaction of alcohols with strong acid, the process of elimination and carboxylation can be conveniently carried out in a single flask. The carbonium ions generated are subject to the... 

Possible use of enzymes for the direct carboxylation of organic substrates... 

ENZYMES CATALYZING THE DIRECT CARBOXYLATION OF HETEROCYCLIC COMPOUNDS... 

An original mechanism involving the formation of an electrophilic Pd(ll) species was proposed to explain the inter-molecular /raor-arylpalladation process (Scheme 15), although more recent work has suggested a Pd(0) pathway. 68,6811 The non-directed carboxylation of arenes is mediated by Pd(ll), although regioselectivities would appear to be poor (Equations (69) and (70)). Very recent examples include Refs 69 and 69a. 

The direct carboxylation of unsaturated compounds has already been reported [107,108]. The process is however limited to reducible alkenes like aryl olefins or activated olefins. On the other hand, only a few examples of direct electrocarboxylation of alkynes have been reported [109],... 

Fig. 5. (a and b) Two perpendicular orientations of direct carboxylate-zinc interactions retrieved from four metalloprotein structures contained in the Brookhaven Protein Data Bank. Orientation (a) represents the carboxylate group as found in Fig. 3. The coordination stereochemistry is syn for each example.

Because salicylic acid contains the deactivating meta-directing carboxyl group, Friedel-Crafts reactions are generally inhibited. This effect is somewhat offset by the presence of the activating hydroxyl group. Salicylic acid reacts with isobutyl or /-butyl alcohol in 80 wt % sulfuric acid at 75°C to yield 5-/-butylsalicylic acid [16094-31-8], In the case of isobutyl alcohol, the intermediate carbonium ion rearranges to (CH3)3C+. 

Carboxylic acid derivatives are compounds that possess an acyl group (R—C=0) linked to an electronegative atom, e.g. —Cl, —CO2 R, —OR or —NH2. They can be converted to carboxylic acids via simple acidic or basic hydrolysis. The important acid derivatives are acid chlorides, acid anhydrides, esters and amides. Usually nitriles are also considered as carboxylic acid derivatives. Although nitriles are not directly carboxylic acid derivatives, they are conveniently hydrolysed to carboxylic acids by acid or base catalysts. Moreover, nitriles can be easily prepared through dehydration of amides, which are carboxylic acid derivatives. 

Ketones of the form RCOCH3 and RCOCH2R can be carboxylated indirectly by treatment with magnesium methyl carbonate 52.613 Because formation of the chelate 53 provides the driving force of the reaction, carboxylation cannot be achieved at a disubstituted a position. The reaction has also been performed on CH3N02 and compounds of the form RCH2N02614 and on certain lactones.61s Direct carboxylation has been reported in a number of instances. Ketones have been carboxylated in the a position to give (3-keto acids.616 The base here was lithium 4-methyl-2,6-di-f-butylphenoxide. 

Recent work shows that a phenoxide-C02 complex is formed competitively with direct carboxylation. This does not go on to form products, but rather decomposes to phenoxide and carbon dioxide. (Y. Kosugi, Y. Imaoka, F. Gotoh, M. A. Rahim, Y. Matsui, K. Sakanishi, Organic and Biomolecular Chemistry 2003,1, 817)... 

Carboxylation.2 Ultrasonically dispersed zinc powder in DMF promotes direct carboxylation (COz or dry ice) of perfluoroalkyl iodides. 

Direct carboxylation reactions (generation of the moieties C-COOH, C-COOR, N-COOR, N-CO-N, -NCO). 

In general a phenol will undergo direct carboxylation of the nucleus when the dry sodium salt is heated under pressure with carbon dioxide (the Kolbe-Schmidt reaction). Addition of the weakly electrophilic carbon dioxide is promoted by electron release from the oxyanionic site. With phenol itself the ultimate product is salicylic acid (o-hydroxybenzoic acid) predominantly ortho attack may be attributable to stabilisation of the transition state through chelation. 

Pyrazinecarboxylic acid has been obtained by selenious acid oxidation in pyridine of methylpyrazine or aqueous permanganate oxidation of ethylpyrazine, in yields of 64 and 48%, respectively.171,218 It has also been obtained in 70% yield by partial decarboxylation of pyrazine-2,3-dicarboxylic acid on heating in vacuo at 210°.219 Aqueous permanganate oxidation of 2,5-distyrylpyrazine gives the 2,5-dicarboxylic acid.220 Pyrazine-2,5-dicarboxylic acid has also been prepared in 45% yield by direct carboxylation of pyrazine with carbon dioxide at 50 atm pressure at 250° for 3 hours in the presence of a potassium carbonate and calcium fluoride catalyst.221 Pyrazine-tricarboxylic acid (57), obtainable in only very poor yields by oxidation of 2,5-dimethyl-3-ethylpyrazine, is prepared in 87% yield by alkaline permanganate oxidation of 2-(D-arabo)tetrahydroxybutyl-quinoxaline (56).222 Decarboxylation of the tricarboxylic acid by... 

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