Diastereoselective addition of silyl metals to γ-alkoxy substituted α,β-unsaturated esters

Dimethylphenylsilyllithium adds to Z-γ-alkoxy-α,β-unsaturated esters to produce almost exclusively (i) the anti-adducts when the reaction is carried out in THF and (ii) the anti-adduct when carried out in the presence of HMPA. Poor stereocontrol is achieved with stereoisomeric E-γ-alkoxy-α,β-unsaturated esters.