Carboxylic acids from arene oxidation

Oxidation of Other Arenes. Aromatic compounds with longer alkyl side chains can be converted to ketones or carboxylic acids. All the previously discussed reagents except Cr02Cl2 usually afford the selective formation of ketones from alkyl-substituted arenes. Oxidation with Cr02Cl2 usually gives a mixture of products. These include compounds oxidized in the P position presumably formed via an alkene intermediate or as a result of the rearrangement of an intermediate epoxide.110,705... 

The first stage (addition-elimination) is well known with CN and a variety of N-, O- and S-nucleo-philes.7-72-75 The detachment of the product arene from the Fe is more difficult. The conversions in equation (22) demonstrate the stability of the arene-Fe bond toward oxidation, as a side chain methyl is converted to a carboxylic acid, and suggest the generality of heteroatom substitution under mild conditions.76... 

Cobalt complexes have been used to catalyze the carbonylation of chloroarenes to the corresponding carboxylic acids and their esters (Sect. 3.3). Some complexes of cobalt in the oxidation state -1 activate the Ar-Cl bond via an SRN1-type mechanism [2] involving single electron transfer from the metal to chloro-arene, followed by elimination of Cl . The simplest Co(-I) carbonyl species, [Co(CO)4] , is not electron-rich enough to react with haloarenes. However, its reactivity has been shown to enhance tremendously in the presence of Caubere s complex bases, mixtures of NaH and NaOAlk [23,66,67]. For instance, the stoichiometric carbonylation of chlorobenzene has been performed with the... 

Several useful synthetic methodologies are based on the generation of the oxygen-centered radicals from carboxylic acids and the (diacetoxyiodo)benzene-iodine system [613-617]. In particular, a direct conversion of 2-substituted benzoic acids 566 into lactones 567 via oxidative cyclization induced by [bis(acyloxy)iodo]arene/iodine has been reported (Scheme 3.224) [613,614]. 

In parallel with progress on the oxidation of alkanes to alcohols and alkyl halides have been reports on the oxidative carbonylations of alkanes and arenes to form carboxylic acids. Fujiwara showed that stoichiometric amounts of arylpalladium acetates formed from the reaction of Pd(OAc)j with arenes and that the resulting arylpalladium complex reacts with CO in acetic acid to form aromatic acids (Equation 18.22). When O, BuOOH, alkyl halides, or K SPj were added as oxidant, the reaction became catalytic in palladium, and benzoic acids were generated from benzene, CO, and the oxidant in the presence of palladium acetate (Equation 18.23). Tl-ie highest yields were obtained with KjSPg as oxidant. Sen has reported related oxidation reactions in acidic media. - ... 

Hydroxyphenazine-l-carboxylic acid (li) and 2-hy-droxyphenazine (lb) are believed to be derived sequentially from phenazine-1-carboxylic acid (Ih) via known biotransformation reactions, presumably via an arene oxide intermediate (Scheme 3). In Pseudomonas aureofaciens, an NADPH-dependent reductase is responsible for the hydroxylation to form li, whereas the subsequent decarboxylation to give lb occurs spontaneously and nonenzymatically. ... 

Organic peroxy acids are well-known reagents for aromatic hydroxylation of arenes [42, 43]. m-Chloroperbenzoic acid was applied to prepare quinones in low to moderate yields [54]. Peroxy acids can be generated in situ from and carboxylic acids or via aldehyde autoxidation [42]. Arnold et al. reported the synthesis of menadione in ca. 30% yield by using 30% in acetic acid [55]. Following this strategy, Orita et al. oxidized a range of arenes by an excess of in formic... 

The synthesis of relevant biaryls has also been reported with aryltrifluoroborates directed by the carboxylic acid functional group in addition to oxidative dimerization. Sanford has described the preparation of biaryls via two discrete C—H functionalizations through the intermediacy of a Pd(IV) fcis-cyclopalladated moiety which reductively eliminates to afford the new C—C bond (Scheme 3.3). An analogous procedure affording the homo-coupled arene from the unactivated starting material has also been reported. ... 

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 ... 

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