Lewis acid catalysts Baeyer-Villiger oxidation

The same Pt species that epoxidize double bonds are active in Baeyer-Villiger oxidation of ketones. Strukul has shown that this synthetically interesting process can be carried out also enantioselectively, in the presence of appropriate diphosphine ligands121-123. For this reaction a mechanism has been proposed that involves again a quasi-peroxo metallacycle intermediate, even though in this reaction the metal catalyst plays primarily the role of a Lewis acid while the real oxidant is H2O2 itself (Scheme 9). 

A fluorous surfactant covalently tethered to silica provides a thin film of perfluorinated solvent for reactions and/or extractions. This material was used for the small-scale hydrocyclization of 6-bromo-1-hexene with NaBH and a catalytic amount of a fluorous tin bromide in 1-butanol. The yield of methylcyclopentane was modest, however, and this technology is a long way from being viable on an industrial scale. The same idea has been more successfully employed with fluorous silica-supported tin Lewis acid catalysts for Baeyer-Villiger oxidations. ... 

Scheme 3.11 Baeyer-Villiger oxidation of ketones to the corresponding lactones. The oxidations were conducted in a fluorous biphasic medium in the presence of the fluorous tin(IV) complex 28 as Lewis acid catalyst. The selectivity is defined as the ratio of the quantity of lactone formed to that of ketone used [29].

Strukul has recently shown that platinum catalyst [(triphosPO)Pt]2+ used to promote the Baeyer-Villiger oxidation with H2O2 operated by Lewis acid catalysis and promoted the leaving of the OH group.33 This dual catalysis property was considered unique to Pt catalysts. Chiral platinum systems have been applied to cyclic ketones to give moderate enantioselectivity of lactones.32... 

A further important development in the use of silica zeolite polymorphs containing Lewis acid sites in the framework in selective oxidation reactions was made by the group of Corma. They found that tin-containing zeolite Beta is a highly selective catalyst for Baeyer-Villiger oxidations, in which ketones are oxidised by hydrogen peroxide to give esters or lactones (Scheme 9.8). ... 

Ishihara and Uyanik [20] observed that complexes between lipophilic ion pairs such as Li[B(C6p4)4] and carboxylic acid work as Lewis acid-assisted Bronsted acid catalysts for the Baeyer-Villiger oxidation. For example, in the presence of 1 mol% of Li[B(C6p4)4] and 5 mol% of oxalic acid, fhe Baeyer-Villiger oxidation of cyclobutanone 19b gave the corresponding y-lactones 20b and 20b under mild conditions ( heme 9). 

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