3- arene- carbon dioxide carboxylic acid

Iodonium salts with a hydroxyl or a carboxyl group are readily converted into their inner salts, i.e. zwitterionic compounds of various types. 2-(Phenyliodonio) benzoate, whose structure may be cyclic, belongs to this category it is prepared from o-iodobenzoic acid upon oxidation and coupling with benzene (or arenes) [51], On strong heating, iodobenzene and carbon dioxide are eliminated, with formation of benzyne ... 

Last year s report described an account of the reductive carboxylation of arenes to give dihydroarene carboxylic acids when they were irradiated in the presence of carbon dioxide and amines. Another group has now reported that biphenyl and 2-phenyl-N-methyllndole both undergo carboxylation in very low yield when irradiated in the presence of carbon dioxide and anilines. 

Iwasawa et al. [21] also reported chelation-assisted reactions in an article entitled Rhodium(I)-Catalyzed Direct Carboxylation of Arenes with CO2 via Chelation-Assisted C-H Bond Activation, in which the cyclometalation reactions proceed easily and form cyclometalation intermediates. The metal atoms are active centers in their intermediates. Hence, the active metal atom reacts easily with inert carbon dioxide to give carboxylic acid derivatives. Examples include the cyclometalation of 2-phenylpyridine as a substrate in the presence of a rhodium intermediate. Carbon dioxide can be inserted into the rhodium-phenyl carbon bond, and a methyl ester is formed with TMSCH2N2 from a rhodium carboxylate, as shown in Eq. (6.5). The reaction mechanism is proposed as shown in Scheme 6.2 [21]. 

Electrochemical carboxylation of a-halogenated arenes under the carbon dioxide atmosphere with zinc anode afforded the effective formation of phenylpropionic acid derivatives in high yield. This method is application of carboxylation of aromatic halides with reactive metal anode to synthesis of a f -inflammatory pharmaceutical drugs. 

The direct reaction of indoles with carbon dioxide at atmospheric pressure to give the 3-carboxylated derivatives has been reported. The reaction occurs in dimethyl for-mamide in the presence of a large excess in lithium t-butoxide whose function is to deprotonate the indole. Although the N-H proton is more acidic, the C(3) anion yields the thermodynamically more stable carboxylated product. Acyl transfer from amides, such as A-(4-nitrophenyl)acetamide to benzene may occur in triflic acid. The mechanism is likely to involve diprotonation of the amide, as shown in (39), and dissociation of the C-N bond to give an acyl cation. The methodology allows the formation of aromatic ketones by inter- or intra-molecular reaction. The acylation of arenes may also be... 

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