Science of Synthesis

Yan, L.; Lin, S.; Liu, P., Science of Synthesis, (2007) 20, 747.

Samarium(II) iodide catalyzes the Tishchenko reduction of β-hydroxy ketones to afford monoesters of anti-1,3-diols in high yields with excellent stereochemical control (anti/syn generally >99:1).[‌82‌] In this procedure, known as the Evans–Tishchenko reaction, a hemiacetal intermediate is formed from a hydroxy ketone ‌65‌ and an aldehyde. This intermediate incorporates the samarium catalyst in a chair-like transition state ‌66‌, which facilitates an intramolecular, highly stereoselective hydride transfer to provide a monoester ‌67‌ of the appropriate anti-1,3-diol (‌Scheme 23‌). A simple illustration, the formation of the hydroxy benzoate ‌68‌ from 5-hydroxy-2,6-dimethylheptan-3-one, is depicted in ‌Scheme 23‌,[‌82‌] but since its discovery, the Evans–Tishchenko reaction has been widely used in the synthesis of more complex polyketide natural products that contain an anti-1,3-diol fragment.[‌83‌–‌87‌] ‌Scheme 23‌ also shows three such applications; thus, the β-hydroxy ketone ‌69‌ is regioselectively reduced to give the ester ‌70‌ in 76% yield.[‌88‌] Similarly, the aldehyde ‌71‌, which contains electron-rich sulfur atoms, is converted into the corresponding ester ‌72‌ in 70% yield,[‌89‌] and in the final illustration the highly functionalized aldehyde ‌73‌ is converted into the ester ‌74‌ in an almost quantitative yield.[‌90‌] Catalysts based on other transition metals can also be employed in the Evans–Tishchenko reaction, including scandium(III) trifluoromethanesulfonate,[‌91‌] a zirconocene complex [Zr(Cp)2H2],[‌92‌] trimethylaluminum,[‌93‌] binuclear aluminum alkoxide,[‌94‌] and zirconium(IV) tert-butoxide.[‌95‌]

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References