Evans-Tishchenko Reaction
The Evans–Tishchenko reaction is the diastereoselective reduction of β-hydroxy ketones to the corresponding anti 1,3-diol monoesters. The reaction employs a Lewis acid, often samarium iodide, and an aldehyde.
Evans-Tishchenko Reaction
Reaction Mechanism
The reaction mechanism involves the attack of the aldehyde from the free alcohol group. The Lewis acid can then chelate between the two oxygen atoms to form a cyclic, 6-membered transition state. Subsequent hydride shift leads to the regeneration of the catalyst and formation of the product.
Experimental Procedure
To a solution of the β-hydroxy ketone (5.0 mmol, 1.0 eq) and propionaldehyde (50 eq) in anhydrous THF (50 mL) under Ar was added dropwise freshly prepared SmI2 (0.1 M solution in THF, 1.1 eq) at ‒10 °C. The solution was warmed to room temperature and stirred for an additional 2 h before quenching with sat. aq. NaHCO3 and extracted with ether. The combined organic layers were dried over Na2SO4 and concentrated under reduced pressure. Purification of the crude residue via silica gel flash column chromatography gave the corresponding anti 1,3-diol monoester (90% yield).
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