Science of Synthesis

Suffert, J., Science of Synthesis, (2005) 26, 936.

The oxidation of titanium enolates ‌208‌, derived from the transmetalation reactions of the corresponding lithium enolates with titanium chlorides [TiCl(OiPr)3, TiCl(NEt2)3, or Ti(Cp)2Cl2], with dimethyldioxirane in acetone represents a general, convenient, effective, and selective approach to α-hydroxy ketones ‌209‌ (‌Scheme 97‌).[‌186‌] The oxidation step is performed at −78°C and normally gives only the corresponding α-hydroxy ketone. When the enolate is chiral the products are formed diastereoselectively, and while some control is possible with alkali metal enolates, titanium enolates are much better substrates. For example, although the oxidation of the sodium enolate of menthone ‌210‌ (M = Na) with dimethyldioxirane gives the corresponding hydroxy ketone in a diastereomeric excess of only 34%, the titanium enolate ‌210‌ [M = Ti(Cp)2Cl] affords the same product in a diastereomeric excess of 92%, although the chemical yield is lower (63 vs 76%) (‌Scheme 97‌).[‌186‌] Similar conversions are also possible when the chlorotitanocene enolates are treated with lithium tert-butylperoxide, formed from 1 equivalent of butyllithium and tert-butyl hydroperoxide (‌Scheme 97‌).[‌187‌]

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α-Meeeeee Meeeeee ‌888‌ Meeee Meeeeeeeeeeeeeeee; Meeeeee Meeeeeeee:[‌888‌]

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α-Meeeeee Meeeeee ‌888‌ Meeee eeee-Meeee Meeeeeeeeeeee; Meeeeee Meeeeeeee:[‌888‌]

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References