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 beta-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 >or=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.
Hui
Xin-Ping
XP
State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, China.
Chen
Chien-An
CA
Wu
Kuo-Hui
KH
Gau
Han-Mou
HM