Shimasaki Toshiaki, Kato Shin-ichiro, Ideta Keiko, Goto Kenta, Shinmyozu Teruo
Institute for Materials Chemistry and Engineering (IMCE) and Department of Molecular Chemistry, Graduate School of Sciences, Kyushu University, Hakozaki 6-10-1, Higashiku, Fukuoka 812-8581, Japan.
J Org Chem. 2007 Feb 16;72(4):1073-87. doi: 10.1021/jo061127v.
Novel photoswitchable chiral hosts having an axis chiral 2,2'-dihydroxy-1,1'-binaphthyl (BINOL)-appended stiff-stilbene, trans-(R,R)- and -(S,S)-1, were synthesized by palladium-catalyzed Suzuki-Miyaura coupling and low-valence titanium-catalyzed McMurry coupling as key steps, and they were fully characterized by various NMR spectral techniques. The enantiomers of trans-1 showed almost complete mirror images in the CD spectra, where two split Cotton effects (exciton coupling) were observed in the beta-transitions of the naphthyl chromophore at 222 and 235 nm, but no Cotton effect was observed in the stiff-stilbene chromophore at 365 nm. The structures of (R)-10 and trans-(R,R)-1 were confirmed by X-ray structural analysis. The optimized structure of cis-1 by MO calculations has a wide chiral cavity of 7-8 A in diameter, whereas trans-1 cannot form an intramolecular cavity based on the X-ray data. Irradiation of (R,R)-trans-1 with black light (lambda = 365 nm) in CH3CN or benzene at 23 degrees C led to the conversion to the corresponding cis-isomer, as was monitored by 1H NMR, UV-vis, and CD spectra. At the photostationary state, the cis-1/trans-1 ratio was 86/14 in benzene or 75/25 in CH3CN. On the other hand, irradiation of the cis-1/trans-1 (75/25) mixture in CH3CN with an ultra-high-pressure Hg lamp at 23 degrees C (lambda = 410 nm) led to the photostationary state, where the cis-1/trans-1 ratio was estimated to be 9/91 on the basis of the 1H NMR spectra. The cis-trans and trans-cis interconversions could be repeated 10 times without decomposition of the C=C double bond. Thus, a new type of photoswitchable molecule has been developed, and trans-1 and cis-1 were quite durable under irradiation conditions. The guest binding properties of the BINOL moieties of trans- and cis-(R,R)-1 with F-, Cl-, and H2PO4- were examined by 1H NMR titration in CDCl3. Similar interaction with F- and Cl- was observed in trans-1 (host/guest = 1/1, Kassoc = (1.0 +/- 0.13) x 103 for F- and (4.6 +/- 0.72) x 102 M-1 for Cl-) and cis-1 (host/guest = 1/1, Kassoc = (1.0 +/- 0.13) x 103 for F- and (5.9 +/- 0.69) x 10 M-1 for Cl-), but H2PO4- interacted differently: the cis-isomer formed the 1/1 complex (Kassoc = (9.38 +/- 2.67) x 10 M-1), whereas multistep equilibrium was expected for the trans-isomer.
以钯催化的铃木-宫浦偶联反应和低价钛催化的麦克默里偶联反应为关键步骤，合成了具有轴手性2,2'-二羟基-1,1'-联萘（BINOL）修饰的刚性二苯乙烯的新型光开关手性主体，即反式-(R,R)-1和-(S,S)-1，并通过各种核磁共振光谱技术对其进行了全面表征。反式-1的对映体在圆二色光谱中显示出几乎完全镜像的特征，在萘发色团的β跃迁中，于222和235 nm处观察到两个分裂的科顿效应（激子耦合），但在365 nm处的刚性二苯乙烯发色团中未观察到科顿效应。通过X射线结构分析确定了(R)-10和反式-(R,R)-1的结构。通过分子轨道计算得到的顺式-1的优化结构具有直径为7-8 Å的宽手性空腔，而根据X射线数据，反式-1无法形成分子内空腔。在23℃下，在乙腈或苯中用黑光（λ = 365 nm）照射(R,R)-反式-1，通过1H NMR、紫外可见光谱和圆二色光谱监测到其转化为相应的顺式异构体。在光稳态下，苯中顺式-1/反式-1的比例为86/14，乙腈中为75/25。另一方面，在23℃下用超高压汞灯（λ = 410 nm）照射乙腈中的顺式-1/反式-1（75/25）混合物至光稳态，根据1H NMR光谱估计顺式-1/反式-1的比例为9/91。顺反和反顺互变可以重复10次而不破坏C=C双键。因此，开发了一种新型的光开关分子，反式-1和顺式-1在照射条件下相当稳定。通过在CDCl3中进行1H NMR滴定，研究了反式和顺式-(R,R)-1的BINOL部分与F-、Cl-和H2PO4-的客体结合性能。在反式-1（主体/客体 = 1/1，F-的缔合常数Kassoc = (1.0 ± 0.13)×103 M-1，Cl-的缔合常数Kassoc = (4.6 ± 0.72)×102 M-1）和顺式-1（主体/客体 = 1/1，F-的缔合常数Kassoc = (1.0 ± 0.13)×103 M-1，Cl-的缔合常数Kassoc = (5.9 ± 0.69)×10 M-1）中观察到与F-和Cl-的类似相互作用，但H2PO4-的相互作用不同：顺式异构体形成1/1配合物（缔合常数Kassoc = (9.38 ± 2.67)×10 M-1），而反式异构体预期会出现多步平衡。
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