Carboxy inversion reaction

Another carboxy inversion reaction has been noted in the case of di-triptoyl peroxide decomposing in benzene.118... 

Benzoyl peroxide appears to decompose entirely by the radical mechanism, the reaction being rather insensitive either to solvent changes or to the addition of acid catalysts. The unsymmetrical peroxide, -methoxy-/> -nitrobenzoyl peroxide, behaves quite differently. It will decompose either by the polar mechanism or by the radical mechanism.821 The radical mechanism prevails in benzene and the acids produced are -nitrobenzoic and anisic in equal amounts. In the more polar solvents anisic acid is formed to a lesser extent than is >-nitrobenzoic acid, because the carboxy inversion reaction (rearrangement) competes successfully. The reaction is subject to acid catalysis... 

The Claisen rearrangement of lactonic enolates provides a new route to cycloalkenes. Cyclocitral was converted to the lactone (642) through a multistep sequence, the lactone deprotonated with LDA in THF at -78 °C, and the enolate quenched with f-butyldimethyl-chlorosilane (80JA6889, 6891). The crude ketene acetal (643) was heated at 110 °C for 10 h, and the product treated with fluoride ion to afford a single acid. Replacement of the quaternary carboxyl group by hydroxyl was accomplished through use of the carboxy inversion reaction (Scheme 147). The product (645) of this last reaction was identical with an authentic sample of widdrol in all respects excluding its optical rotation. 

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... 

Carboxy-inversion reaction. Denney and Sherman found that m-chloroperbenzoic acid (2) reacts readily with a carboxylic acid chloride (1) in hexane solution at 0 in the presence of pyridine to form a mixed peroxide (3). When the mixture is stirred for several hours at room temperature the peroxide rearranges to the mixed carbonate... 

Diacyl peroxides, which are known as radical sources, can decompose by an ionic mechanism in the presence of strong acids. Thus, benzoyl peroxide 282 can be converted into phenyl benzoate in a process whose first step involves a Lewis acid catalyzed carboxy inversion reaction to the mixed carbonate 283 (equation 134). ... 

Wittig elaboration and ketone reduction, ester hydrolysis, acetylation and treatment with dicyclohexylcarbodiimide and m-chloroperbenzoic acid afforded the mixed peranhydride (26b). Transformation of (26b) to (3b) was achieved by means of a carboxy inversion reaction which occurred, with retention of configuration, on refluxing in acetonitrile, and treatment of the resulting mixed carbonate with lithium methoxide. 

Diacyl peroxides may also undergo non-radical decomposition via the carboxy inversion process to form an acylcarbonate (Scheme 3.27).46 The reaction is of greatest importance for diaroyl peroxides with electron withdrawing substituents and for aliphatic diacyl peroxides (36) where R is secondary, tertiary or ben/,yl.157 The reaction is thought to involve ionic intermediates and is favored in polar solvents 57 and by Lewis acids.158 Other heterolytic pathways for peroxide decomposition have been described.150... 

Carboxylate anions derived from somewhat stronger acids, such as p-nilrobcnzoic acid and chloroacetic acid, seem to be particularly useful in this Mitsunobu inversion reaction.53 Inversion can also be carried out on sulfonate esters using cesium carboxy-lates and DMAP as a catalyst in toluene.54 The effect of the DMAP seems to involve complexation and solubilization of the cesium salts. 

As is the case in conventional solvents, competing radical and ionic processes (Scheme 4.8) were needed to explain the observed products and reaction kinetics in the decomposition of diacyl peroxides in sc C02 (Sigman et al., 1987). In addition to ArC02R and other products attributable to free-radicals, carboxy inversion products were observed, which result from ionization of the diacyl peroxide (Scheme 4.8). 

Inversion of the configuration in the cyclization reaction has been demonstrated for the (R)-bromo acid (490) which can be made from (R)-cysteine. The product (491) from the cyclization has the S configuration. By choice of reaction conditions to promote rearrangement, some of the enantiomeric 2-carboxy isomer (492) can be obtained (81H(15)1349). 

The reaction proceeds stereospecifically with inversion of configuration at the carbon-oxygen bond that is converted into a carbon x hlorine bond. Thus treatment of D-( — )-2-carboxy-2,4,5-trimethyl-1,3-dioxolane (10) yields i.- + )-erythro-3-ch oro-2-butyl acetate (11). Treatment of (11) with KOH in ethylene glycol yields n-(-t )-2,3-cpoxybulane (12), a reaction known to proceed with inversion at the carbon-halogen bond. 

This would cause an increase in the melt viscosity of the elastomer phase relative to polyamide, thus preventing a phase inversion [Saltman, 1992 Ohme, 1991], At the same time, the compatibility between the ionomer and polyamide as well as some degree of reactive compatibilization between E-BA-GMA and polyamide (through carboxy/epoxide or amine/epoxide reactions) may lead to the stabilization of the dispersions. 

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