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

1
College of Chemistry and Healthy Food Evaluation Research Center, Sichuan University, Chengdu 610064, China
2
Institute of Environmental Sciences, Department of Chemistry, Shanxi University, Taiyuan 030006, China
3
Shanghai Advanced Research Institute, Chinese Academy of Science, Shanghai 201210, China
*
Authors to whom correspondence should be addressed.
Symmetry 2019, 11(6), 773; https://doi.org/10.3390/sym11060773
Received: 16 May 2019 / Revised: 31 May 2019 / Accepted: 4 June 2019 / Published: 9 June 2019
(This article belongs to the Special Issue Chiral Auxiliaries and Chirogenesis II)
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 RP (RP, RP, RP, RP, and RP)- and SP (SP, SP, SP, SP, and SP)-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 CH2Cl2 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. View Full-Text
Keywords: pillar[5]arene; planar chirality; chiral resolution; racemization kinetics; supramolecular chemistry pillar[5]arene; planar chirality; chiral resolution; racemization kinetics; supramolecular chemistry
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MDPI and ACS Style

Xiao, C.; Liang, W.; Wu, W.; Kanagaraj, K.; Yang, Y.; Wen, K.; Yang, C. Resolution and Racemization of a Planar-Chiral A1/A2-Disubstituted Pillar[5]arene. Symmetry 2019, 11, 773.

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