The oxidation of an acyclic ketone to an ester, or a cyclic ketone to a lactone (the Baeyer-Villiger reaction) can be achieved with the help of metal species of the Lewis acid type.27 Chiral copper(II), palladium(II), and titanium(IV) catalysts
Figure 11.14 Enantioselective Baeyer-Villiger oxidation.
Figure 11.15 Enantioselective Baeyer-Villiger oxidation.
have been developed for enantioselective processes, but the reaction protocols are quite specific, and yields and enantioselectivity are only moderate. For example, copper(II) oxazoline catalysts in combination with pivaldehyde and oxygen selectively oxidize one enantiomer of a racemic compound to the desired lactone, and fail to react with the other, thereby generating enantioselectivity (Figure 11.14)28
A more recent variant of the enantioselective Baeyer-Villiger oxidation involves an aluminium complex of BINOL, together with a chiral hydroperoxide, and gives similar levels of enantioselectivity (Figure 11.15)29
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