Kambara T, Tomioka K
Graduate School of Pharmaceutical Sciences, Kyoto University, Japan.
Chem Pharm Bull (Tokyo). 2000 Oct;48(10):1577-80. doi: 10.1248/cpb.48.1577.
A catalytic amount of external chiral bisoxazoline ligand 3a bearing an isopropyl group as a stereocontrolling group catalyzed a reaction of a lithium ester enolate 4b, generated from 3-pentyl 2-methylpropionate, with benzaldehyde anisidine-imine 5 to afford corresponding beta-lactam 6 in higher 70% ee than that obtained by the reaction using a stoichiometric amount of the ligand. A bulkier ligand 3d bearing a phenyl group gave 81% and 6% ees in stoichiometric and catalytic reactions, respectively. Examination of the varying factors suggested the involvement of mixed aggregates as a reactive species. A working model is presented for prediction of the sense of asymmetric induction.
催化量的带有异丙基作为立体控制基团的外消旋双恶唑啉配体3a催化了由2-甲基丙酸3-戊酯生成的锂酯烯醇化物4b与苯甲醛茴香胺亚胺5的反应，得到相应的β-内酰胺6，其对映体过量（ee）为70%，高于使用化学计量的该配体进行反应所得到的ee值。带有苯基的体积更大的配体3d在化学计量和催化反应中分别给出了81%和6%的ee值。对各种变化因素的研究表明，混合聚集体作为反应物种参与其中。提出了一个用于预测不对称诱导方向的工作模型。
