Oxygenative Decarboxylation

Hnally, a useful, although not strictly a radical, meAod of effecting decarboxylative oxygenation is Ae so-called carboxy inversion reaction. The activated acid is transformed into a mixed all l aryl diacyl peroxide which suffers decarboxylative rearrangement to Ae alkyl ester of the aryl acid. This reaction is particularly useful as it takes place wiA retention of configuration at the migrating center (equation... 

In 2008, Stoltz et al. reported the first synthesis of elatol 217 (Scheme 1.38) [47]. Starting from dimedone, the mixed carbonate 218 was prepared. Decarboxylative oxygen-to-carbon migration was effected using a Pd(0) complex based on the chiral... 

Diacyl Peroxides. Table 3 Hsts several commercial diacyl peroxides and their corresponding 10-h half-hfe temperatures, deterrnined in benzene and other solvents (32). Although diacyl peroxides cleave at the oxygen—oxygen bond, decarboxylation can occur, either simultaneously or subsequentiy (eq. 22) ... 

The extent of decarboxylation primarily depends on temperature, pressure, and the stabihty of the incipient R- radical. The more stable the R- radical, the faster and more extensive the decarboxylation. With many diacyl peroxides, decarboxylation and oxygen—oxygen bond scission occur simultaneously in the transition state. Acyloxy radicals are known to form initially only from diacetyl peroxide and from dibenzoyl peroxides (because of the relative instabihties of the corresponding methyl and phenyl radicals formed upon decarboxylation). Diacyl peroxides derived from non-a-branched carboxyhc acids, eg, dilauroyl peroxide, may also initially form acyloxy radical pairs however, these acyloxy radicals decarboxylate very rapidly and the initiating radicals are expected to be alkyl radicals. Diacyl peroxides are also susceptible to induced decompositions ... 

This ladical-geneiating reaction has been used in synthetic apphcations, eg, aioyloxylation of olefins and aromatics, oxidation of alcohols to aldehydes, etc (52,187). Only alkyl radicals, R-, are produced from aliphatic diacyl peroxides, since decarboxylation occurs during or very shortiy after oxygen—oxygen bond scission in the transition state (187,188,199). For example, diacetyl peroxide is well known as a source of methyl radicals (206). 

Until recent years the only syntheses of 3-hydroxy quinoline involved multistep processes, the last step of which consisted of the conversion of 3-aminoquinoline to 3-hydroxyquinoline via the diazonium salt. " Small quantities of quinoline have been oxidized to 3-hydroxyquinoline in low yields by using oxygen in the presence of ascorbic acid, ethylenediaminetetraacetic acid, ferrous sulfate, and i)hosi)halc buffer. The decarboxylation of 3-hydroxycinchoninic, acid in boiling nitrobenzene has been re-... 

Nilrosated fluoro compounds are frequently prepared by electrophilic nitrosation on an electron-nch center of oxygen, nitrogen, or carbon The preparation of fluorochloronitronitrosomethane from the decarboxylation of fluorochloronitro-acetic acid in nitric acid is unique [f ] (equation 1)... 

In the absence of oxygen, these thiolene-2-ones are rather stable and have been kept at 0°C for several months. 3-Hydroxythiophene, on the other hand, which has been prepared in low yield from 3-thio-phenemagnesium bromide in the same way as the 2-isomer, or through decarboxylation of 3-hydroxy-2-thiophenecarboxylic acid, "" is very unstable. Its IR spectrum indicates that it also exists as a tautomeric mixture largely in its enolic form. ... 

Decarboxylation of isoxazole-3-carboxylic acids is related to the nucleophilic cleavage of the isoxazole ring as far as the nature of the reaction products is concerned. It occurs at temperatures above 200°C and is accompanied by the cleavage of the nitrogen-oxygen bond of the heterocyclic ring to yield a j8-ketonitrile. It was first reported by Claisen with 5-methyl- and 5-phenyl-isoxazole-3-carboxylic acids (153- 154).Under the reaction conditions, j8-ketonitriles condense... 

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