CATALYTIC ASYMMETRIC ADDITION OF POLYFUNCTIONAL DIALKYLZINCS TO BETA-STANNYLATED AND BETA-SILYLATED UNSATURATED ALDEHYDES

The addition of functionalized dialkylzincs to readily available beta-stannylated or beta-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 blacks is demonstrated. The gamma-stannylated allylic alcohols were submitted to a Stille coupling leading to polyfunctional allylic alcohols and gamma-alkoxy enones. A treatment with CuCN in N-methylpyrrolidone at 130 degrees C provided chiral unsaturated gamma-hydroxy nitriles. Finally, the desilylation of the gamma-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.