Abstract
The Lewis acid mediated aldol-type reaction of nucleophilic alkenes (alkyl enol ethers, enol esters) has been investigated since 1939 and is well documented in the literature. 1 The first breakthrough in this field was in 1973–74 when Mukaiyama and coworkers found that silyl enol ethers are much more effective than alkyl enol ethers in Lewis acid mediated additions to carbonyl compounds. 2 This is related to the fact that silicon is markedly more electropositive than carbon (1.8 versus 2.5), resulting in a stronger polarization of Si O bonds and in a stronger tendency for nucleophilic attack at silicon with consequent Si O bond heterolysis. 3 Since then the ’Mukaiyama reaction‘ has become a useful chemo- and regio-selective synthetic method. During the 1980s several researchers made a second breakthrough by succeeding in making this reaction diastereo- and enantio-selective. These stereochemical aspects are the subject of the present review. The reader should be aware that progress in this area is still rapid and that some of the tentative conclusions drawn in this review are likely to change. Because of the mass of data that has accrued in this field, this chapter is selective and critical rather than exhaustive. The reader is referred to earlier reviews for further discussion of individual points. 3,4
Published Version
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