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

College of Chemistry and Healthy Food Evaluation Research Center, Sichuan University, Chengdu 610064, China
Institute of Environmental Sciences, Department of Chemistry, Shanxi University, Taiyuan 030006, China
Shanghai Advanced Research Institute, Chinese Academy of Science, Shanghai 201210, China
Authors to whom correspondence should be addressed.
Symmetry 2019, 11(6), 773;
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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