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The Mukaiyama aldol addition is a Lewis acid-mediated addition of enol silanes to carbonyl (C=O) compounds. In this reaction, compounds with various organic groups can be used (see educts). [ 3 ] A basic version ( R 2 = H) without the presence of chiral catalysts is shown below.
The aldol reaction (aldol addition) is a reaction in organic chemistry that combines two carbonyl compounds (e.g. aldehydes or ketones) to form a new β-hydroxy carbonyl compound. Its simplest form might involve the nucleophilic addition of an enolized ketone to another:
A Mukaiyama aldol addition (magnesium bromide / toluene) took place between aldehyde 7 and ketene silyl acetal 8 with 71% stereoselectivity to alcohol 9 which was protected as the TBS ether 10 (TBSOTf, 2,6-lutidine). The ester group was reduced with DIBAL to an alcohol and then back oxidized to aldehyde 11 by Swern oxidation.
Silyl enol ethers are used in many reactions resulting in alkylation, e.g., Mukaiyama aldol addition, Michael reactions, and Lewis-acid-catalyzed reactions with S N 1-reactive electrophiles (e.g., tertiary, allylic, or benzylic alkyl halides).
Then aldol, the aldol addition product itself is then formed. After which it may undergo dehydration to give a unsaturated carbonyl compound, the aldol condensation product. The scheme shows a simple mechanism for the base-catalyzed aldol reaction of an aldehyde with itself. Base-catalyzed aldol reaction
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The first two reactions shown below are from the syntheses of (+)-lycoflexine [32] and zaragozic acid C, [33] respectively, which are direct applications of Sakurai and Mukaiyama reactions. The third reaction, en route to (+)-fawcettimine, is a Lewis-acid catalyzed cyclopropane opening that is analogous to a Mukaiyama-Michael reaction. [34]
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