A Lewis Acid Promoted Asymmetric Umpolung Reaction with ChiralN-Sulfinyl Imines as the Electrophiles
作者:Xin Xu、Jun-ying Liu、Dian-jun Chen、Cody Timmons、Guigen Li
DOI:10.1002/ejoc.200400775
日期:2005.5
An new asymmetric umpolung reaction has been developed by reacting N-sulfinyl imines with 2-lithio-2-phenyl-1,3-dithiane. The reaction was conducted at between –20 and–25 °C in THF in the presence of Et2AlCl as the Lewis acid promoter. Excellent diastereoselectivities (up to >95 % de) and chemical yields (64–95 %) have been achieved for nine substrates with all individual isomers separated and characterized
通过将 N-亚磺酰基亚胺与 2-lithio-2-phenyl-1,3-dithiane 反应,开发了一种新的不对称 umpolung 反应。在 Et2AlCl 作为路易斯酸促进剂存在的情况下,反应在 –20 至 –25 °C 的 THF 中进行。九种底物实现了出色的非对映选择性(高达 >95% de)和化学产率(64–95%),所有单独的异构体都被分离和表征。手性产物的绝对结构已通过合成转化为已知样品明确确定。发现 2-Lithio-2-phenyl-1,3-dithiane 的反应性远低于其 2-甲基对应物,这是最近报道的。所有单独的异构体都可以很容易地通过柱色谱分离。手性产物的绝对结构已通过转化为已知化合物明确确定。这种方法可以轻松获得对映异构纯的 α-氨基酮。(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)