Chemistry of Unique Chiral Olefins. 2. Unexpected Thermal Racemization of cis-1,1‘,2,2‘,3,3‘,4,4‘-Octahydro-4,4‘- biphenanthrylidene
Chemistry of Unique Chiral Olefins. 2. Unexpected Thermal Racemization of cis-1,1‘,2,2‘,3,3‘,4,4‘-Octahydro-4,4‘- biphenanthrylidene
复制标题
独特手性烯烃的化学。 2. cis-1,1,2,2,3,3,4,4-八氢-4,4-联菲的意外热外消旋化
DOI：
10.1021/ja970668m
复制
发表时间：
1997
影响因子：
15
通讯作者：
B. Feringa
中科院分区：
文献类型：
--
作者：
N. Harada;A. Saito;N. Koumura;D. Roe;W. Jager;R. Zijlstra;B. D. Lange;B. Feringa
在研究独特的手性烯烃（E）-1，1 '，2，2'，3，3 '，4，4'-八氢-4，4 '-联菲叉（1）及其（Z）-异构体（2）的过程中，我们发现顺式烯烃（2）在室温下发生了意想不到的热消旋反应。旋光化合物2的CD光谱显示出强度的快速下降，在室温下半衰期t1/2 = 1.2 h。在CD Cotton效应消失后，通过具有手性固定相的HPLC检查顺式烯烃2的样品，并且检测到顺式烯烃2的两种对映体，但从未检测到反式烯烃1。空间位阻较大的顺式烯烃2的外消旋化通过两种对映异构体（M，M）-（Z）-2和（P，P）-（Z）-2之间的直接相互转化而发生，而不形成作为中间体的反式烯烃1。用核磁共振磁化转移技术研究了2的两个对映体之间的相互转化。通过CD和NMR光谱研究，得到了2的对映体互变动力学数据，并由此得到了2的活性。
During the studies of the unique chiral olefins, (E)-1,1‘,2,2‘,3,3‘,4,4‘-octahydro-4,4‘-biphenanthrylidene (1) and its (Z)-isomer (2), we found the unexpected thermal racemization of cis-olefin 2 at room temperature. The CD spectrum of optically active 2 shows rapid decrease of intensity with the half-life time t1/2 = 1.2 h at room temperature. After the CD Cotton effects vanish, the sample of cis-olefin 2 was checked by HPLC with a chiral stationary phase, and two enantiomers of cis-olefin 2 were detected, but trans-olefin 1 was never detected. The racemization of sterically more-hindered cis-olefin 2 occurs by the direct interconversion between the two enantiomers (M,M)-(Z)-2 and (P,P)-(Z)-2 without formation of trans-olefin 1 as an intermediate. The enantiomeric interconversion between the two enantiomers of 2 was also studied by the 1H NMR magnetization transfer technique. The kinetic values of the enantiomeric interconversion of 2 were obtained by CD and NMR spectroscopic studies and lead to an activ...