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)cyclohexan e (8 mol%) provides chiral allylic alcohols in good yields (60-90%) an d excellent enantioselectivity (usually in the range of 85-95% ee). Th e synthetic utility of these allylic alcohols as chiral building black s is demonstrated. The gamma-stannylated allylic alcohols were submitt ed 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. Fina lly, the desilylation of the gamma-silylated alcohols gave chiral ally lic alcohols having a terminal double bond. The catalytic asymmetric a ddition was found to show an important inverse temperature dependance. A mechanism for this addition is proposed.