Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan.
J Am Chem Soc. 2020 Oct 28;142(43):18317-18323. doi: 10.1021/jacs.0c09080. Epub 2020 Oct 16.
Enantioconvergent intramolecular coupling of α-(2-bromobenzoylamino)benzylboronic esters was achieved using a copper catalyst having helically chiral macromolecular bipyridyl ligand, PQXbpy. Racemic α-(2-bromobenzoylamino)benzylboronic esters were converted into ()-configured 3-arylisoindolinones with high enantiopurity using right-handed helical PQXbpy as a chiral ligand in a toluene/CHCl mixed solvent. When enantiopure ()- and ()-configured boronates were separately reacted under the same reaction conditions, both afforded ()-configured products through formal stereoinvertive and stereoretentive processes, respectively. From these results, a mechanism involving deracemization of organocopper intermediates in the presence of PQXbpy is assumed. PQXbpy switched its helical sense to left-handed when a toluene/1,1,2-trichloroethane mixed solvent was used, resulting in the formation of the corresponding ()-products from the racemic starting material.
使用具有螺旋手性大分子联吡啶配体 PQXbpy 的铜催化剂，实现了 α-(2-溴苯甲酰氨基)苄基硼酸酯的对映体收敛的分子内偶联。在甲苯/CHCl 混合溶剂中，使用右手螺旋 PQXbpy 作为手性配体，将外消旋的 α-(2-溴苯甲酰氨基)苄基硼酸酯转化为具有高对映纯度的 ()-构型 3-芳基异吲哚啉酮。当对映纯的 ()-和 ()-构型硼酸酯分别在相同的反应条件下反应时，它们分别通过正式的立体反转和立体保留过程，得到 ()-构型产物。根据这些结果，假设在 PQXbpy 的存在下，有机铜中间体的消旋化涉及到一种机制。当使用甲苯/1,1,2-三氯乙烷混合溶剂时，PQXbpy 会将其螺旋方向切换为左手，从而从外消旋起始原料中形成相应的 ()-产物。
