Polystyrene‐supported N ‐sulfonylated amino alcohols and their applications to titanium(IV) complexes catalyzed enantioselective diethylzinc additions to aldehydes

Crosslinked polystyrene‐supported resins 4 , 7a , and 7b containing N ‐sulfonylated β‐amino alcohol in 98, 20, and 40% loadings are prepared. Asymmetric diethylzinc additions to benzaldehyde employing titanium complexes of 10 mol % resins 4 , 7a , or 7b are examined and the best performed 7a /Ti(O‐ i ‐Pr) 4 catalytic system applies to various aldehydes to afford desired secondary alcohols in excellent enantioselectivities up to 95% ee. The resin 7a is reused five times, giving the product with enantioselectivities ≥86% ee and an 81% ee is obtained when the resin is used the sixth time. The used resin 7a is refreshed with 1 M HCl and the asymmetric reaction employing the regenerated resin 7a gives the product in 88% ee. Chirality, 2006. © 2006 Wiley‐Liss, Inc.