Abstract
The addition of functionalized dialkylzincs to readily available β-stannylated or β-silylated unsaturated aldehydes in the presence of a catalytic amount of (1R,2R)-1,2-bis(trifluorosulfonamido)-cyclohexane (8 mol%) provides chiral allylic alcohols in good yields (60-90%) and excellent enantioselectivity (usually in the range of 85-95% ee). The synthetic utility of these allylic alcohols as chiral building blocks id demonstrated. The γ-stannylated allylic alcohols were submitted to a Stille coupling leading to polyfunctional allylic alcohols and γ-alkoxy enones. A treatment with CuCN in N-methylpyrrolidone at 130°C provided chiral unsaturated γ-hydroxy nitriles. Finally, the desilylation of the γ-silylated alcohols gave chiral allylic alcohols having a terminal double bond. The catalytic asymmetric addition was found to show an important inverse temperature dependance. A mechanism for this addition is proposed
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