Cationic Ir/Me-BIPAM-Catalyzed Asymmetric Intramolecular Direct Hydroarylation of α-Ketoamides
作者:Tomohiko Shirai、Hajime Ito、Yasunori Yamamoto
DOI:10.1002/anie.201400147
日期:2014.3.3
Asymmetricintramoleculardirecthydroarylation of α‐ketoamides gives various types of optically active 3‐substituted 3‐hydroxy‐2‐oxindoles in high yields with complete regioselectivity and high enantioselectivities (84–98 % ee). This is realized by the use of the cationic iridium complex [Ir(cod)2](BArF4) and the chiral O‐linked bidentate phosphoramidite (R,R)‐Me‐BIPAM.
α-酮酰胺的不对称分子内直接氢芳基化反应可高产率获得各种类型的旋光3-取代3-羟基2-羟吲哚,具有完全的区域选择性和高对映选择性(84–98%ee)。这是通过使用阳离子铱络合物[Ir(cod)2 ](BAr F 4)和手性O联双齿亚磷酰胺(R,R)-Me-BIPAM来实现的。
Scope and Mechanistic Studies of the Cationic Ir/Me-BIPAM-Catalyzed Asymmetric Intramolecular Direct Hydroarylation Reaction
作者:Tomohiko Shirai、Yasunori Yamamoto
DOI:10.1021/om501260w
日期:2015.7.27
Results of mechanistic studies on asymmetric hydroarylation of alpha-keto amides Via direct C-H bond addition to a carbonyl group catalyzed by a cationic Ir/Me-BIPAM complex are presented in this paper. A catalytic cycle involving C-H bond cleavage to give an Ar-[Ir](+) intermediate, insertion of a carbonyl group into the aryl-iridium bond, giving iridium alkoxide, and finally reductive elimination to reproduce active [Ir](+) species is proposed. The mechanistic insight for the iridium hydride species indicated that the C-H bond cleavage is caused in a reversible manner. Furthermore, the kinetic isotope effect was measured by product analysis of the reaction to compare HID, and it was determined that k(H)/k(D) was 1.85. These experimental results suggest that the C-H bond cleavage step is not included hi the turnover-limiting step. In addition, Hammett studies of substrates (rho = -0.99) demonstrated that electron-donating groups at the para position to the reactive C-H bond accelerate the reaction rate. This linear relationship obtained in the Hammett plot indicates that the nucleophilicity of the aryl-iridium intermediate is an important factor in this reaction. All of the data indicate that carbonyl insertion into aryl-iridium is included in the turnover-limiting step of the catalytic cycle.