Some new results on asymmetric synthesis via the addition of α-metalated methyl tolyl sulfoxides to imines are presented. Good diastereoselectivity (up to >98% d.e. for product 3g) can be obtained under conditions of kinetic control (short reaction time, low temperature). The transition state (a six-membered "flat chair") was probed by quantum mechanical calculations, which underpinned the idea of using external chiral ligands to enhance the diastereoselectivity of otherwise moderately selective reactions. In this way, the diastereomeric ratio of the product 3a could be raised from (84:16) to (>99:1) by use of a readily available C2-symmetric bis(sulfonamide) ligand.
介绍了通过将α-
金属化甲基
甲苯亚磺酰氧化物加入
亚胺中进行不对称合成的一些新结果。在动力学控制条件下(反应时间短,温度低),可以获得良好的对映选择性(产品3g的对映选择性高达> 98%)。量子力学计算探测到了过渡态(六元“平椅”),从而支持了使用外部手性
配体增强反应对映选择性的想法。通过使用易得的C2-对称双(磺酰胺)
配体,可以将产物3a的对映异构比从(84:16)提高到(> 99:1)。