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 enantio selective 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 start ing materials for a number of stereoselective reactions. Acylsilanes o f this type upon treatment with organometallic reagents gave rise to 1 ,2-addition products with high degrees of stereoselectivities. The res pective alpha-hydroxysilanes could be stereospecifically desilylated t o chiral secondary alcohols, or, depending on the substitution pattern , further used as starting compounds for stereocontrolled oxidation, C ope- or Claisen-type rearrangement reactions. Chiral alpha-metallated vinyl-silanes were converted to alpha-silyl-substituted allylic alcoho ls and to alpha-substituted alpha,beta-unsaturated ketones. The prior led to chiral allenes in a Peterson-type reaction - however, without s tereoselectivity - the latter delivered stereoselectively beta-chiral silicon-free ketones upon stereocontrolled conjugate cuprate addition followed by removal of the silicon auxiliary.