Oxidations of ketones

The ability of the R or R groups to migrate determines the ease of reaction and which products dominate in the case of unsymmetrical ketones. The following sequence is observed for the migratory tendency of different groups  

The nature of the migrating group is not, however, the sole factor determining the outcome of a particular reaction the acidity of the reaction medium237 and the nature of the oxidant238 also have an influence. 

Under these conditions, however, stable peroxides may form and polymerization of lactones can occur. Lewis acids, e.g. BF3, SbFs, have been used to activate hydrogen peroxide in similar Baeyer-Villiger oxidations.241 

Whilst yields are generally low, this is a useful method for preparing large ring compounds, including a number of important musk compounds used in perfumes. 

Baeyer-Villiger reactions also occur under alkaline conditions, although poorer results are usually obtained compared with the use of peracids (see 

C-C bond breaks as alkyl group shuts to oxygen 

Baeyer-Villiger oxidation of a cyclic ketone results in a cyclic ester (a lactone) with a ring that has been expanded. Note that the stereochemistry of the carbon center involved in the migration is retained during the oxidation. 

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Baeyer-Villiger Oxidation- oxidation of ketones to esters and lactones via oxygen insertion... 

Section 17 16 The oxidation of ketones with peroxy acids is called the Baeyer-Vilhger oxidation and is a useful method for preparing esters... 

Earlier reports have indicated that esters can form before significant amounts of acids accumulate (16). The Bayer-ViUiger oxidations of ketones with intermediate hydroperoxides and/or peracids have been suggested as ester forming mechanisms (34,56). However, the reactions of simple aUphatic ketones with peracetic acid are probably too slow to support this mechanism (57,58). Very early proposals for ester formation, although imaginative, appear improbable (59). 

The Baeyer-Villiger oxidation of ketones to esters (or lactones) occurs by the following mechanism. 

While the oxidation of ketones by peracids (Baeyer-Villiger reaction) has been used in steroids mainly for ring cleavage, it has occasionally been applied to 20-ketopregnanes for conversion to 17-acetoxy- or hydroxyandros-tanes. The synthetic utility of this method is limited since reactive double bonds and other ketones are incompatible with the reagent. 

A. Perbenzoic Acid Oxidation of Ketones General Procedure (10)... 

In extrahepatic tissues, acetoacetate is activated to acetoacetyl-CoA by succinyl-CoA-acetoacetate CoA transferase. CoA is transferred from succinyl-CoA to form acetoacetyl-CoA (Figure 22-8). The acetoacetyl-CoA is split to acetyl-CoA by thiolase and oxidized in the citric acid cycle. If the blood level is raised, oxidation of ketone bodies increases until, at a concentration of approximately 12 mmol/L, they saturate the oxidative machinery. When this occurs, a large proportion of the oxygen consumption may be accounted for by the oxidation of ketone bodies. 

Discussion of ketone oxidation has centred around the identity of the molecule undergoing oxidation. This has been clearly resolved in some, but not all, cases, the evidence resting on (i), the relative rates of enolisation and oxidation, (ii) kinetic orders and (ih) isotope effects. A general feature of the oxidations of ketones by one-equivalent reagents is that the rate for a given oxidant exceeds that for oxidation of a secondary alcohol by the same oxidant. The most attractive explanation is that the radical formed from a ketone is stabilised by delocalisation, viz. 

An interesting catalytic effect upon the alkaline ferricyanide oxidations of ketones is shown by osmium(VIII) tetroxide, the rate expression being... 

Oxidation of Ketones and Aldehydes 12.5.1. Transition Metal Oxidants... 

Oxidation of Ketones and Aldehydes by Oxygen and Peroxidic Compounds... 

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