Conformationally Rigid Chiral Bicyclic Skeleton-Tethered Bipyridine<i>N,N′-</i>Dioxide as Organocatalyst: Asymmetric Ring Opening of<i>meso</i>-Epoxides
作者:Elumalai Gnanamani、Nagamalla Someshwar、Jayakumar Sanjeevi、Chinnasamy Ramaraj Ramanathan
DOI:10.1002/adsc.201400029
日期:2014.7.7
N′‐dioxide (−)‐9 has been designed, synthesized and examined as an organocatalyst in the enantioselective ring opening of meso‐epoxides using tetrachlorosilane (SiCl4). The catalyst (−)‐9 is found to exhibit good enantioselectivity for substituted cis‐stilbene epoxides; whereas, the saturated cyclic meso‐epoxides display a moderate enantioselectivity. At −30 °C in chloroform, the catalyst (−)‐9 with 0
使用四氯硅烷(SiCl 4)设计,合成和检查了构象刚性的手性双环骨架束缚联吡啶N,N'-二氧化氮(-)- 9作为有机催化剂。发现催化剂(-)- 9对取代的顺式-二苯乙烯环氧化物具有良好的对映选择性;而,饱和环状内消旋环氧化物显示适度的对映选择性。在−30°C的氯仿中,负载量为0.5 mol%的催化剂(−)‐ 9生成氯醇,产率高达97%,ee高达93%。由于构象刚性的手性双环骨架束缚的联吡啶N,N'-二氧化物的存在,可能在高价硅物种周围产生短暂的轴向手性环境,这可能是介观中环氧化物去对称化中这种对映选择性的原因。