Reinhold Tacke, Haryanto Linoh, Burghard Stumpf, Wolf-Rainer Abraham, Klaus Kieslich, Ludger Ernst

• The trimethylsilylalkyl acetoacetates 1 b and 2 b as well as their carba analogues 1 a and 2 a have been reduced microbiologically by Kloeckera corticis (ATCC 20109), leading to the corresponding ( + )-3(S)-hydroxybutanoates 3b, 4b, 3a, and 4a. The enantiomeric purity was found to be 80% (3a, 3b, 4b) and 65% (4a), respectively. The reduction of lb and 2b is - to our knowledge - the first example for a controlled microbiological transformation of organosilicon substrates.