Chiral Non-Planar Oligophenylenes bridged by Urea Linkage: Synthesis through Intramolecular Direct Arylation, Chiroptical Behavior, and Theoretical Investigation
Chiral Non-Planar Oligophenylenes bridged by Urea Linkage: Synthesis through Intramolecular Direct Arylation, Chiroptical Behavior, and Theoretical Investigation
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通过脲键桥接的手性非平面低聚亚苯基：通过分子内直接芳基化、手性光学行为和理论研究进行合成
DOI：
10.1002/ejoc.201900191
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发表时间：
2019
影响因子：
2.8
通讯作者：
I. Azumaya
中科院分区：
文献类型：
--
作者：
K. Takagi,* Y. Hirano;K. Mikami,* S. Kikkawa;I. Azumaya
用钯催化剂对N，N′-二己基- N′-（2 -溴苯基）- N′-苯脲进行分子内直接芳化反应，产率达75%。同样制备了长terphenyl化合物（TPbU）。其他四种共轭低聚物（BPtU、BPU‐1Np、BPU‐2Np和BPU‐Ant）均由bpuin在短反应步骤中合成。X射线晶体学表明，具有硫脲骨架的bptu具有准C=N双键性质。每个对映体在手性高效液相色谱上进行光学拆分，显示镜像棉花效应和单信号CD模式。通过高效液相色谱法评估了对映体过量（ee.）值，bpud和tpbu具有相当的外消旋能垒（ΔG‡rac= 23.3 kcal mol-1和23.4 kcal mol-1）。bptu的外消旋能势垒相当高（ΔG‡rac= 30.1 kcal mol-1），这可能是由于准C=N双键的性质。另一方面，BPU - 2nn和BPU - Anthaving π -共轭体系分别表现出23.8 kcal mol-1和24.0 kcal mol-1的ΔG‡racrac1。理论分析很好地解释了这些实验结果。
The intramolecular direct arylation ofN,N′‐dihexyl‐N‐(2‐bromophenyl)‐N′‐phenylurea using palladium catalyst gaveBPUin 75 % yield. Longer terphenyl compound (TPbU) was likewise prepared. Other four conjugated oligomers (BPtU,BPU‐1Np,BPU‐2Np, andBPU‐Ant) were synthesized fromBPUin short reaction steps. From the X‐ray crystallography,BPtUwith the thiourea skeleton was suggested to have a quasi C=N double bond character. Each enantiomer was optically resolved on chiral HPLC to show mirroring Cotton effects and monosignate CD patterns. The enantiomeric excess (ee.) values were evaluated by HPLC, from whichBPUandTPbUexhibited comparable racemization energy barriers (ΔG‡rac= 23.3 kcal mol–1and 23.4 kcal mol–1). The racemization energy barrier ofBPtUwas considerably high (ΔG‡rac= 30.1 kcal mol–1) likely due to the quasi C=N double bond character. On the other hand,BPU‐2NpandBPU‐Anthaving the π‐conjugated system exhibited ΔG‡racof 23.8 kcal mol–1and 24.0 kcal mol–1, respectively. These experimental results were well explained by theoretical analyses.