Graduate School of Life and Environmental Sciences, Kyoto Prefectural University, 1-5 Hangi-cho, Shimogamo, Sakyo-ku, Kyoto 606-8522, Japan.
Division of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba, Tenodai 1-1-1, Tsukuba, Ibaraki 305-8571, Japan.
J Org Chem. 2021 Dec 17;86(24):17620-17628. doi: 10.1021/acs.joc.1c01726. Epub 2021 Nov 24.
Bridged indigos were synthesized by bridging the two nitrogen atoms in the indigo structure with a carbon chain, and their properties were carefully examined. These bridged indigos have intrinsic planar chirality, and the enantiomers were separated using chiral high-performance liquid chromatography. When the chiral bridged indigos were subjected to thermo- and photoisomerization, the corresponding ()-indigo was not observed at all, and racemization was observed. This phenomenon is caused by the low activation energy of inversion due to the 1.5 bond order of the double bond of the indigo skeleton and the large energy difference between the ground states of ()-indigo and ()-indigo.
桥连靛蓝是通过在靛蓝结构的两个氮原子之间桥接一个碳链合成的，并对其性质进行了仔细的研究。这些桥连靛蓝具有内在的平面手性，并使用手性高效液相色谱法分离对映异构体。当手性桥连靛蓝发生热和光异构化时，根本没有观察到相应的 ()-靛蓝，而是观察到外消旋化。这种现象是由于靛蓝骨架双键的 1.5 键级导致反转的活化能较低，以及 ()-靛蓝和 ()-靛蓝的基态之间的能量差较大所致。
