Synthesis and Structural and Photoswitchable Properties of Novel Chiral Host Molecules: Axis Chiral 2,2‘-Dihydroxy-1,1‘-binaphthyl-Appended stiff-Stilbene1

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 β-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 Å 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 (λ = 365 nm) in CH3CN or benzene at 23 °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 °C (λ = 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) × 103 for F-
and (4.6 ± 0.72) × 102 M-1 for Cl-) and cis-1 (host/guest = 1/1, Kassoc = (1.0 ± 0.13) × 103 for F- and
(5.9 ± 0.69) × 10 M-1 for Cl-), but H2PO4- interacted differently:  the cis-isomer formed the 1/1 complex
(Kassoc = (9.38 ± 2.67) × 10 M-1), whereas multistep equilibrium was expected for the trans-isomer.

本研究成功合成了新颖的、光控手性主体，该主体具备轴手性2,2'-二羟基-1,1'-双萘基(BINOL)附加的刚性苯乙烯基团。合成过程以钯催化的Suzuki-Miyaura偶联反应和低价钛催化的McMurry偶联反应为关键步骤。通过多种核磁共振光谱技术对其进行了全面表征。在CD光谱中，trans-1的对映异构体展现出近乎完美的镜像，并在萘基发色团的β-跃迁处观察到222和235 nm处的两个分裂的科顿效应(激子耦合)，但在365 nm处的刚性苯乙烯发色团中未观察到科顿效应。通过X射线结构分析确认了(R)-10和trans-(R,R)-1的结构。大语言模型(MO)计算优化后的cis-1结构具有直径为7-8 Å的宽手性腔，而trans-1根据X射线数据无法形成分子内腔。在23°C下，以365 nm的黑光照射(R,R)-trans-1于CH3CN或苯中，可将其转化为相应的cis异构体，这一转化过程可通过1H NMR、UV-vis和CD光谱进行监测。在光稳态下，苯中的cis-1/trans-1比为86/14，而CH3CN中的比为75/25。另一方面，在23°C下，使用超高压汞灯照射cis-1/trans-1(75/25)混合物于CH3CN中至光稳态，根据1H NMR光谱，估计cis-1/trans-1比为9/91。cis-trans和trans-cis之间的相互转换可重复进行10次而不导致C=C双键的分解。因此，一种新型的光控分子已被开发出来，trans-1和cis-1在光照条件下表现出极高的稳定性。通过在CDCl3中进行的1H NMR滴定实验，研究了trans-和cis-(R,R)-1的BINOL基团与F-、Cl-和H2PO4-的客体结合特性。在trans-1和cis-1中，均观察到与F-和Cl-的相似相互作用：(host/guest = 1/1，F-的Kassoc = (1.0 ± 0.13) × 10^3，Cl-的Kassoc = (4.6 ± 0.72) × 10^2 M^-1)，而H2PO4-的相互作用则有所不同：cis异构体形成了1/1的复合物(Kassoc = (9.38 ± 2.67) × 10^M^-1)，而trans异构体则预期会形成多步骤的平衡。