Baeyer-Villiger oxidations, effective

Baeyer-Villiger oxidation effected by H2G2.HO Ac. It is noteworthy to point out... 

The key steps in the ring expansion of the cyclobutanones (186) and (787) are the Baeyer-Villiger oxidation effected by H202—HOAc. It is noteworthy to point out that the Baeyer-Villiger oxidation is regiospecific and serves to be an excellent method for the preparation of y-lactone from cyclobutanones. 

Parallel to the modification of the catalytic performance in Baeyer-Villiger oxidations, random mutagenesis was successfully applied to improve the stereoselectivity of CHMOAcineto hi cascs of essentially racemic sulfoxide formation. In addition, enantiodivergent clones with >98% ee for both antipodal products were identified (Table 9.5) [205]. However, improvement in stereoselectivity of mutant enzymes was often accompanied by increased formation of sulfone. This effect can also be utilized to resolve racemic sulfoxides. 

For the oxidation of ketones, Baeyer-Villiger oxidation of cyclic ketones with monopersuccinic acid in water gives lactones in good results (Eq. 8.22).47 Peroxy species generated from borax in 30% hydrogen peroxide is effective for the Baeyer-Villiger oxidation of... 

A high catalyst loading (typically 20-30 mol%) is usually required for the epoxidation with ketone 26 because Baeyer-Vilhger oxidation presumably decomposes the catalyst during the epoxidation. The fused ketal moiety in ketone 26 was replaced by a more electron-withdrawing oxazohdinone (32) and acetates (33) with the anticipation that these replacements would decrease the amount of decomposition via Baeyer-Villiger oxidation (Fig. 8) [71, 72]. Only 5 mol% (1 mol% in some cases) of ketone 32 was needed to get comparable reactivity and enantioselectivity with 20-30 mol% of ketone 26 [71]. Since dioxiranes are electrophilic reagents, they show low reactivity toward electron-deficient olefins, such as a, 3-unsaturated esters. Ketone 33, readily available from ketone 26, was found to be an effective catalyst towards the epoxidation of a, 3-unsaturated esters [72]. 

Co(ni) alkyl peroxides have been prepared and used by Mimoun and coworkers in the hydroxylation of hydrocarbons with this metal a Haber-Weiss type of reactivity is suggested. Square-planar Pt(II) complexes, of the type [(dppe)Pt(CF3)(solv)], used by Strukul in the epoxidation of alkenes and in Baeyer-Villiger oxidations of ketones (Schemes 8 and 9), are effective catalysts also in the direct hydroxylation of aromatics with hydrogen peroxide. The reactivity increases in the presence of electron releasing substituents in the aromatic ring. Ortho and para derivatives are practically the only products observed and interesting selectivity toward the ortho products has been detected (equation 85). 

Baeyer-Villiger oxidation (1, 823-824). Baeyer-Villiger oxidation of very hindered methyl ketones can be effected with trifluoroperacedc acid [(CF3C0)20-H202] in the presence of 1 equivalent of Na2HP04. Use of more than 1 equivalent of Na2HP04 results in a slower reaction and a lower yield.1... 

Baeyer- Villiger oxidations7 This peroxide in combination with trimethylsilyl Inflate (1 equiv.) is highly effective for selective Baeyer-Villiger oxidation of acyclic anil cyclic ketones, but not of aromatic ketones, without epoxidation of carbon-carbon double bonds, lixamples ... 

The Baeyer-Villiger transformation of several protected derivatives having a free ketone group has been effected by m-chloroperoxybenzoic acid. Thus, 1,6-anhydro-3,4-0-isopropylidene-/f-D-/yxn-hexopyranos-2-ulose (28) was converted into the cyclic, orthoacid anhydride 29.67 As an additional example, the Baeyer-Villiger oxidation of Ferrier carbocyclization products derived from D-glucose afforded 5-deoxyhexofuranosiduronic acids, via the ring-expanded lactonic intermediates68 (Scheme 12). 

Baeyer-Villiger oxidation.1 Since 90% H202 is no longer readily available owing to hazards in its preparation, alternative reagents for Baeyer-Villiger reactions are particularly desirable. m-Chloroperbenzoic acid (80-85%) as such is not always effective, but addition of TFA (1 1) enhances the reactivity and the yield. 

Another one-step addition reaction to C=C double bonds that forms three-membered rings is the epoxidation of alkenes with percarboxylic acids (Figure 3.19). Most often, meta-chloroperbenzoic acid (MCPBA) is used for epoxidations. Magnesium monoperoxyphthalate (MMPP) has become an alternative. Imidopercarboxylic acids are used to epoxidize olefins as well. Their use (for this purpose) is mandatory when the substrate contains a ketonic C=0 double bond in addition to the C=C double bond. In compounds of this type, percarboxylic acids preferentially cause a Baeyer-Villiger oxidation of the ketone (see Section 14.4.2), whereas imidopercarboxylic acids selectively effect epoxidations (for an example see Figure 14.35). 

Figure 1 Intermolecular and intramolecular 2H and, 3C isotope effects for the Baeyer-Villiger oxidation of cyclohexanone (standard deviations in parentheses).

Figure 4 Effect of the support on the antimony trifluoride-catalysed Baeyer-Villiger oxidation...

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