Locking the Dynamic Axial Chirality of Biphenyl Crown Ethers through Threading

Kimura, Tomoe; Miyagawa, Shinobu; Takaya, Hikaru; Naito, Masaya; Tokunaga, Yuji

doi:10.1002/asia.202001046

Cited by 4 publications

(3 citation statements)

References 60 publications

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“…A much higher value of the racemization barrier was obtained for the pseudo[2]rotaxane 3-Et 2 NH 2 + , namely, 47.1 kcal mol −1 . This value is higher even than the one reported by Kimura et al for urea-rotaxane (45 kcal mol −1 in o-dichlorobenzene, Kimura et al, 2020). A proposed racemization mechanism for the 3-Et 2 NH 2 + species is depicted in Figure 8.…”

Section: Racemization Processesmentioning

confidence: 60%

Solid-State and Theoretical Investigations of Some Banister-Type Macrocycles with 2,2’-Aldoxime-1,1’-Biphenyl Units

et al. 2021

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In the context of helical chirality, bridging of biphenyl units leads to banister-type compounds and the stability of the resulted atropisomers may increase dramatically if suitable changes are performed in the linker unit that coils around the biphenyl moiety. A rigorous density functional theory (DFT) study was conducted for macrocycles containing rigid oxime ether segments connected to the biphenyl backbone in order to determine how the rotation barriers are influenced by the presence of either a flexible oligoethyleneoxide or a more rigid m–xylylene component in the macrocycle. The calculated values for the racemization barrier were in good agreement with those obtained experimentally and confirm the benefit of introducing a more rigid unit in the macrocycle on the stability of atropisomers. Solid-state data were obtained and computed data were used to assess the contribution brought by supramolecular associations observed in the lattice to the stabilization of the crystal structure. Beside introducing rigidity in the linker, complexation of flexible macrocycles with alkali metal ions is also contributing to the stability of atropisomers, leading to values for the racemization barrier matching that of the rigid macrocycle. Using diethylammonium cation as guest for the macrocycle, a spectacular increase in the barrier to rotation was observed for the resulted pseudo[2]rotaxane.

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Section: Racemization Processesmentioning

confidence: 60%

Solid-State and Theoretical Investigations of Some Banister-Type Macrocycles with 2,2’-Aldoxime-1,1’-Biphenyl Units

et al. 2021

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“…The tert -butyl group was not necessary structurally to introduce chirality, but it allowed selective bromination at positon 3 of catechol and simplified the 1 H NMR spectrum of the resulting rotaxane. Macrocyclization of catechol 4 and dichloride 5 gave mono-crown ether 6 , which was converted to this bis-crown ether 1 through biaryl coupling using a Ni catalyst. Variable-temperature (VT) NMR spectroscopy revealed the dynamic chirality of 1 (Figure S1).…”

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confidence: 99%

“…11 Each of these studies focused on the chiral response, such that the axial chiralities were temporary, and diastereoselectivities were not estimated, although Stoddart has investigated precisely the axial chirality in catenanes. 9 Recently, we reported the locking of a potentially chiral biphenyl moiety in the macrocyclic component of an interlocked structure at ambient temperature, 12 but racemization proceeded at higher temperatures.…”

mentioning

confidence: 99%