Mukaiyama aldol addition
The Mukaiyama aldol addition is an organic reaction and a type of aldol reaction between a silyl enol ether and an aldehyde or formate. The reaction was discovered by Teruaki Mukaiyama (born 1927) in 1973. His choice of reactants allows for a crossed aldol reaction between an aldehyde and a ketone or a different aldehyde without self-condensation of the aldehyde. For this reason the reaction is used extensively in organic synthesis.
The Mukaiyama aldol addition is a Lewis acid mediated addition of enol silanes to carbonyl compounds. In this reaction compounds with various organic groups can be used (see educts). A basic version (R2 = H) without the presence of chiral catalysts is shown below.
A racemic mix of enantiomers is built. If Z- or E-enol silanes are used in this reaction a mixture of four products occurs, yielding two racemates.
If the anti-diastereomer or the syn-diastereomer is built largely depends on reaction conditions, substrates and Lewis acids.
The archetypical reaction is that of the silyl enol ether of cyclohexanone with benzaldehyde. At room temperature it produces a diastereomeric mixture of threo (63%) and erythro (19%) β-hydroxyketone as well as 6% of the exocyclic enone condensation product. In its original scope the Lewis acid (titanium chloride) was used in stoichiometric amounts but truly catalytic systems exist as well. The reaction is also optimized for asymmetric synthesis.
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