Highly Enantioselective Bromocyclization of Allylic Amides with a P/P=O Double-Site Lewis Base Catalyst
作者:Yuji Kawato、Hiromi Ono、Akino Kubota、Yoshihiro Nagao、Naoki Morita、Hiromichi Egami、Yoshitaka Hamashima
DOI:10.1002/chem.201503153
日期:2016.2.5
enantioselective bromocyclization of allylic amides catalyzed by phosphorus‐containing Lewis bases was examined in detail. A series of control experiments and NMR studies showed that a partially oxidized bis‐phosphine generated in situ serves as the actual enantioselective catalyst. The reaction mechanism involves distinct roles of two Lewis basic sites, P and P=O, with P+Br serving as a fine‐tuning element
详细检查了含磷路易斯碱催化的烯丙基酰胺的对映选择性溴环化。一系列对照实验和NMR研究表明,原位生成的部分氧化的双膦可作为实际的对映选择性催化剂。该反应机理涉及两个路易斯碱性位点P和P = O的独特作用,其中P + Br用作手性环境中底物固定的微调元素,而P + OBr作为向烯烃的Br +转移剂。催化剂的负载量可降低至1 mol%,并且该反应可提供对映体富集的恶唑啉,其ee最高> 99.5%。