Ketones Meet Their Match

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Science  12 Apr 2002:
Vol. 296, Issue 5566, pp. 221
DOI: 10.1126/science.296.5566.221b

Numerous methods exist for controlling the stereochemistry for the addition of ketones and esters to aldehydes to form an aldol (a β-hydroxy carbonyl). Methods for accomplishing the addition to the less reactive ketones, instead of aldehydes, are few and limited to α-diketones and pyruvate esters. Previous studies have shown that the trichlorosilyl enolate of methyl acetate (1) is highly reactive toward aldehydes, so much so that it is difficult to control the stereochemistry of the outcome. Denmark and Fan now show that 1 will add to a wide variety of ketones, such as acetophenone (2a), but in a highly enantioselective manner in the presence of N-oxide promoters. Mechanistic studies indicate that two catalyst molecules are involved in the transition state, and the authors found that bis-N-oxides gave yields of about 90%, with enantiomeric excesses of 80 to 85%.—PDS

J. Am. Chem. Soc. 10.1021/ja025670e (2002).

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