We have successfully developed the asymmetric hydrogenation of β‐silyl‐α,β‐unsaturatedesters to prepare chiral 3‐substituted‐3‐silylpropionic esterproducts catalyzed by rhodium/bisphosphine‐thiourea (ZhaoPhos) with excellent results (up to 97% yield, >99% ee, 1500 TON). Moreover, our hydrogenation products can be efficiently converted to other important organic molecules, such as chiral ethyl (R
Carbon−Carbon Bond-Forming Enantioselective Synthesis of Chiral Organosilicon Compounds by Rhodium/Chiral Diene-Catalyzed Asymmetric 1,4-Addition Reaction
作者:Ryo Shintani、Kazuhiro Okamoto、Tamio Hayashi
DOI:10.1021/ol051978+
日期:2005.10.1
new syntheticmethod for chiral organosilicon compounds through a rhodium-catalyzed asymmetric 1,4-addition of arylboronic acids to beta-silyl alpha,beta-unsaturated carbonyl compounds has been developed. By employing (R,R)-Bn-bod* as a ligand, a range of arylboronic acids can be coupled with these substrates in very high enantiomeric excess. The resulting beta-silyl 1,4-adducts can be converted to
Acicular purplish crystals were obtained from Cu(acac)(2) and a chiral bipyridine ligand. Although the crystals were not soluble, they nevertheless catalyzed asymmetric silyl conjugate addition of lip ophilic substrates in water. Indeed, the reactions proceeded efficiently only in water; they did not proceed well either in organic solvents or in mixed water/organic solvents in which the catalyst/substrates were soluble. This is in pronounced contrast to conventional organic reactions wherein the catalyst/substrates tend to be in solution. Several advantages of the chiral Cu(II) catalysis in water over previously reported catalyst systems have been demonstrated. Water is expected to play a prominent role in constructing and stabilizing sterically confined transition states and accelerating subsequent protonation to achieve high yields and enantioselectivities.