Stereoselective Transformations Starting with Chiral (Alkoxy)methyl-Substituted Organosilicon Compounds
The following short review summarizes the results we achieved with the investigation of chiral silicon groups as auxiliaries for the enantioselective synthesis. (Alkoxy)methyl-substituted silicon compounds with 'Si-centered chirality', which were prepared in optically active form by application of a bioreduction, have been efficiently used as starting materials for a number of stereoselective reactions. Acylsilanes of this type upon treatment with organometallic reagents gave rise to 1,2-addition products with high degrees of stereoselectivities. The respective α-hydroxysilanes could be stereospecifically desilylated to chiral secondary alcohols, or, depending on the substitution pattern, further used as starting compounds for stereocontrolled oxidation, Cope- or Claisen-type rearrangement reactions. Chiral α-metallated vinylsilanes were converted to α-silyl-substituted allylic alcohols and to α-silyl-substituted α,β-unsaturated ketones. The prior led to chiral allenes in a Peterson-type reaction – however, without stereoselectivity – the latter delivered stereoselectively β-chiral silicon-free ketones upon stereocontrolled conjugate cuprate addition followed by removal of the silicon auxiliary.
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