Guest-regulated chirality switching of planar chiral <i>pseudo</i>[1]catenanes

Yang, Yafen; Hu, Weibo; Shi, Lei; Li, Shenggang; Zhao, Xiao‐Li; Liu, Yahu A.; Li, Jiusheng; Jiang, Biao; Wen, Ke

doi:10.1039/c8ob00156a

Cited by 29 publications

(24 citation statements)

References 32 publications

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“…Normal pillar [5]arenes have two enantiomeric conformers with all hydroquinone ether units adapting a planar chiral R p , (R p , R p , R p , R p , and R p ) or S p , (S p , S p , S p , S p , and S p ) configuration. In general, these two conformers are rapidly interconvertible in a solution by flipping the ring units around the methylene bridges, the so-called oxygen-through-annulus rotation [17]. The inhibition of the oxygen-through-annulus rotation will lead to a pair of planar-chiral enantiomers.…”

Section: Introductionmentioning

confidence: 99%

Resolution and Racemization of a Planar-Chiral A1/A2-Disubstituted Pillar[5]arene

Xiao

Liang

et al. 2019

Symmetry

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Butoxycarbonyl (Boc)-protected pillar[4]arene[1]-diaminobenzene (BP) was synthesized by introducing the Boc protection onto the A1/A2 positions of BP. The oxygen-through-annulus rotation was partially inhibited because of the presence of the middle-sized Boc substituents. We succeeded in isolating the enantiopure R P (R P , R P , R P , R P , and R P )-and S P (S P , S P , S P , S P , and S P )-BP, and studied their circular dichroism (CD) spectral properties. As the Boc substituent is not large enough to completely prevent the flip of the benzene units, enantiopure BP-f1 underwent racemization in solution. It is found that the racemization kinetics is a function of the solvent and temperature employed. The chirality of the BP-f1 could be maintained in n-hexane and CH 2 Cl 2 for a long period at room temperature, whereas increasing the temperature or using solvents that cannot enter into the cavity of BP-f1 accelerated the racemization of BP-f1. The racemization kinetics and the thermodynamic parameters of racemization were studied in several different organic solvents. or bithienyl groups, have been chemically grafted onto one or more hydroquinone ether units, and the oxygen-through-annulus rotation was restrained or completely stopped [21,22]. It occurred to us that if introducing a group of suitable size, the oxygen-through-annulus could still be allowed, but the rotation velocity is slowed down. This will then provide a powerful tool to study the effect of the external factors, such as the temperature and solvent, on the rotational kinetics of pillar[5]arene. Herein, we report on the successful isolation of butoxycarbonyl (Boc)-protected pillar[4]arene-[1]diaminobenzene (BP) planar chiral enantiomers. Two middle-sized Boc-protected substituents on the A1/A2 positions significantly decelerated the flip of pillar[5]arene, to allow for the racemization of BP with an observable velocity. The thermodynamics and kinetics of the racemization were investigated under different solvent and temperature conditions, which may serve as a guideline in the isolation and control of the enantiomeric conformations of pillar[n]arenes by manipulating the external factors. Materials and MethodsAll of the compounds and reagents were obtained from commercial suppliers and were used as received. Chiral analytical HPLC was performed with a Chiralpak IA column (0.46 × 25 cm) by a Shimadzu LC Prominence 20 HPLC instrument (Shimadzu, Tokyo, Japan) equipped with a UV-VIS detector (conditions: injection volume: 20 µL of rac-BP (0.2 mM); mobile phase: hexane/dichloromethane, 70/30 (v/v); flow rate: 1.0 mL/min at 20 • C; retention time (t R ): 5.3 min for BP-f1, 5.7 min for BP-f2). Preparative column chromatography was carried out with a Chiralpak IA column (1.0 × 25 cm) by a recycling preparative HPLC LC9210NEXT instrument (JAI, Tokyo, Japan) equipped with a UV-VIS detector (conditions: injection volume: 3 mL of rac-BP (2 mM); mobile phase: hexane/dichloromethane, 70/30 (v/v); flow rate: 4.0 mL/min at 20 • C; retention time (t R ): 11.4 min ...

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Section: Introductionmentioning

confidence: 99%

Resolution and Racemization of a Planar-Chiral A1/A2-Disubstituted Pillar[5]arene

Xiao

Liang

et al. 2019

Symmetry

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“…The diaminopillar [5]arene-based macrobicyclic molecule (BC-DAP5)w as preparedb ya na lternative multistep synthetic pathway,a sf ully detailed in the Scheme 1. Initially,b yf ollowing ap rocedure previously reported by our group, [25,26] diaminopillar [5]arene DAP5-1 was obtainedi ng ood yield.T he alkylation of DAP5-1 formed dialkylated pillar [5]arene DAP5-2,f ollowed by removing the Bocg roupsw ith trifluoroacetic acid (TFA) to give dienaminopillar [5]arene DAP5-3.T he cyclization of DAP5-3 using Grubbs metathesis [30] afforded the macrobicyclic molecule BC-DAP5,b ut the reactiony ield was very low ( % 9%), which, we believe, could be due to the instability of the diaminophenyl unit or the poison from the naked amino groupst oG rubbs catalyst (Scheme 1, route 1). Thus, Grubbs metathesis was also carried out on the Boc-protected DAP5-2 (Scheme 1, route 2), and,a se xpected, the reactiona fforded DAP5-4 in excellent yield ( % 93 %).…”

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confidence: 97%

“…However, such studies are rare. It will be very interesting if we could control the motion of one or more phenylu nites of pillar[5]arenes, making the rotation have an on/off state.Recently,s everalp illar[5]arene-based macrobicyclic molecules have been reported, [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] and some of them showeda n [a] Dr.Supporting information and the ORCID identification number(s) for the author(s) of this articlecan be found under: https://doi.Scheme2.The schematicrepresentation of the reversible control of BC-DAP5 locked and unlocked states.…”

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confidence: 99%

“…[23,35] Thus, introducing DB into ap illar [5]arene-based macrobicyclic molecule system would switch the bicyclic molecule from the "in" to "out" state in some extent,w hich in the 1 HNMR spectrum would appear as chemical shifts changes,i ft here were "in" state molecules. [23,25,26] Thus, we used DB to studyt he state of BC-DAP5 in solution. As shown in Figure 2a nd Figure S25 protons of the fused ring of BC-DAP5,e specially H a ,s howed no chemical shifts change, demonstrating that no BC-DAP5 in the "in" state could be switched to the "out" state because of the complexation between DB and the pillar [5]arene cavity.I n other words, BC-DAP5 was in the "out" state in solution.…”

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confidence: 99%

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A Diaminopillar[5]arene‐Based Macrobicyclic Molecule: Synthesis, Characterization and A Lock–Key Story

Wang

Zhao

et al. 2019

Chemistry A European J

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A new macrobicyclic molecule (BC‐DAP5), consisting of a diaminopillar[5]arene cavity and a fused ring, was successfully constructed using a Grubbs metathesis reaction. Further studies indicated that BC‐DAP5 possessed a unique molecular behavior, showing a response to acid/base stimuli. In BC‐DAP5, protons (acid) acted as a lock, locking the fused ring out of the cavity (pillar[5]arene), and a base served as the key, making the fused ring switch in or out freely. Reversible control of the molecular behavior was achieved simply by adding acid and base alternately.

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“…Such chiral P[n]s have been realized with P [5], and chirality inversion by solvent, competitive guests, and temperature have been demonstrated. [13] In our studies on supramolecular chirality, [14] we have previously established the correlation of the circular dichroism (CD) spectrum with the absolute configuration of P [5] and demonstrated a temperature-driven chirality inversion of P [5]-based molecular universal joints (MUJ). [7b] However, the correlation between P[6] configuration and CD responses, which is more challenging owing to the difficulty in the synthesis of enantiomeric P[6], has not yet been reported.…”

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Redox‐Triggered Chirality Switching and Guest‐Capture/Release with a Pillar[6]arene‐Based Molecular Universal Joint

Xiao

Liang

et al. 2020

Angewandte Chemie

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A chiral electrochemically responsive molecular universal joint (EMUJ) was synthesized by fusing a macrocyclic pillar[6]arene (P[6]) to a ferrocene-based side ring. A single crystal of an enantiopure EMUJ was successfully obtained, which allowed, for the first time, the definitive correlation between the absolute configuration and the circular dichroism spectrum of a P[6] derivative to be determined. The self-inclusion and self-exclusion conformational change of the EMUJ led to a chiroptical inversion of the P[6] moiety, which could be manipulated by both solvents and changes in temperature. The EMUJ also displayed a unique redoxtriggered reversible in/out conformational switching, corresponding to an occupation/voidance switching of the P[6] cavity, respectively. This phenomenon is an unprecedented electrochemical manipulation of the capture and release of guest molecules by supramolecular hosts.Supporting information and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

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Guest-regulated chirality switching of planar chiral pseudo[1]catenanes

Cited by 29 publications

References 32 publications

Resolution and Racemization of a Planar-Chiral A1/A2-Disubstituted Pillar[5]arene

Resolution and Racemization of a Planar-Chiral A1/A2-Disubstituted Pillar[5]arene

A Diaminopillar[5]arene‐Based Macrobicyclic Molecule: Synthesis, Characterization and A Lock–Key Story

Redox‐Triggered Chirality Switching and Guest‐Capture/Release with a Pillar[6]arene‐Based Molecular Universal Joint

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