The diastereoselective addition of 1,3-bis(trimethylsilyloxy)-1-methoxybutadiene 2 to readily available alpha-heterosubstituted aldehydes (S)-1 affords after syn-diastereoselective reduction HMG-CoA-reductase-inhibitor-precursors (S,R,S)-4 and 5 with various substitution patterns and high enantiomeric and diastereoisomeric excesses (ee = 93- > 96%; de 95- > 96%) in good yields.