Hayashi T, Hirate S, Kitayama K, Tsuji H, Torii A, Uozumi Y
Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo, Kyoto 606-8502, Japan.
J Org Chem. 2001 Feb 23;66(4):1441-9. doi: 10.1021/jo001614p.
In the palladium-catalyzed asymmetric hydrosilylation of styrene (3a) with trichlorosilane, several chiral monophosphine ligands, (R)-2-diarylphosphino-1,1'-binaphthyls (2a-g), were examined for their enantioselectivity. The highest enantioselectivity was observed in the reaction with (R)-2-bis[3,5-bis(trifluoromethyl)phenyl]phosphino-1,1'-binaphthyl (2g), which gave (S)-1-phenylethanol (5a) of 98% ee after oxidation of the hydrosilylation product, 1-phenyl-1-(trichlorosilyl)ethane (4a). The palladium complex of 2g also efficiently catalyzed the asymmetric hydrosilylation of substituted styrenes on the phenyl ring or at the beta position to give the corresponding chiral benzylic alcohols of over 96% ee. Deuterium-labeling studies on the hydrosilylation of regiospecifically deuterated styrene revealed that beta-hydrogen elimination from 1-phenylethyl(silyl)palladium intermediate is very fast compared with reductive elimination giving hydrosilylation product when ligand 2g is used. The reaction of o-allylstyrene (9) with trichlorosilane catalyzed by (R)-2g/Pd gave (1S,2R)-1-methyl-2-(trichlorosilylmethyl)indan (10) (91% ee) and (S)-1-(2-(propenyl)phenyl)-1-trichlorosilylethanes (11a and 11b) (95% ee). On the basis of their opposite configurations at the benzylic position, a rationale for the high enantioselectivity of ligand 2g is proposed.
在钯催化的苯乙烯（3a）与三氯硅烷的不对称硅氢化反应中，考察了几种手性单膦配体，即（R）-2-二芳基膦基-1,1'-联萘（2a - g）的对映选择性。在用（R）-2-双[3,5-双（三氟甲基）苯基]膦基-1,1'-联萘（2g）进行的反应中观察到了最高的对映选择性，在将硅氢化产物1-苯基-1-（三氯硅基）乙烷（4a）氧化后，得到了对映体过量（ee）为98%的（S）-1-苯乙醇（5a）。2g的钯配合物也能有效地催化苯环上或β位取代苯乙烯的不对称硅氢化反应，得到对映体过量超过96%的相应手性苄醇。对区域特异性氘代苯乙烯的硅氢化反应进行的氘标记研究表明，当使用配体2g时，与生成硅氢化产物的还原消除相比，1-苯乙基（硅基）钯中间体的β-氢消除非常快。（R）-2g/Pd催化邻烯丙基苯乙烯（9）与三氯硅烷的反应得到了（1S,2R）-1-甲基-2-（三氯硅基甲基）茚（10）（ee为91%）和（S）-1-（2-（丙烯基）苯基）-1-三氯硅基乙烷（11a和11b）（ee为95%）。基于它们在苄基位置的相反构型，提出了配体2g具有高对映选择性的理由。
