{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,11,9]],"date-time":"2025-11-09T07:45:26Z","timestamp":1762674326187,"version":"build-2065373602"},"reference-count":40,"publisher":"MDPI AG","issue":"6","license":[{"start":{"date-parts":[[2019,6,9]],"date-time":"2019-06-09T00:00:00Z","timestamp":1560038400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Symmetry"],"abstract":"<jats:p>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.<\/jats:p>","DOI":"10.3390\/sym11060773","type":"journal-article","created":{"date-parts":[[2019,6,10]],"date-time":"2019-06-10T03:16:51Z","timestamp":1560136611000},"page":"773","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":18,"title":["Resolution and Racemization of a Planar-Chiral A1\/A2-Disubstituted Pillar[5]arene"],"prefix":"10.3390","volume":"11","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-1668-5062","authenticated-orcid":false,"given":"Chao","family":"Xiao","sequence":"first","affiliation":[{"name":"College of Chemistry and Healthy Food Evaluation Research Center, Sichuan University, Chengdu 610064, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3275-9965","authenticated-orcid":false,"given":"Wenting","family":"Liang","sequence":"additional","affiliation":[{"name":"Institute of Environmental Sciences, Department of Chemistry, Shanxi University, Taiyuan 030006, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8969-1148","authenticated-orcid":false,"given":"Wanhua","family":"Wu","sequence":"additional","affiliation":[{"name":"College of Chemistry and Healthy Food Evaluation Research Center, Sichuan University, Chengdu 610064, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9263-1277","authenticated-orcid":false,"given":"Kuppusamy","family":"Kanagaraj","sequence":"additional","affiliation":[{"name":"College of Chemistry and Healthy Food Evaluation Research Center, Sichuan University, Chengdu 610064, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0785-9446","authenticated-orcid":false,"given":"Yafen","family":"Yang","sequence":"additional","affiliation":[{"name":"Shanghai Advanced Research Institute, Chinese Academy of Science, Shanghai 201210, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Ke","family":"Wen","sequence":"additional","affiliation":[{"name":"Shanghai Advanced Research Institute, Chinese Academy of Science, Shanghai 201210, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2049-1324","authenticated-orcid":false,"given":"Cheng","family":"Yang","sequence":"additional","affiliation":[{"name":"College of Chemistry and Healthy Food Evaluation Research Center, Sichuan University, Chengdu 610064, China"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2019,6,9]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"2325","DOI":"10.1016\/S0040-4039(01)92246-4","article-title":"Induced circular dichroism of benzoylbenzoic acids in \u03b2-cyclodextrin","volume":"15","author":"Takenaka","year":"1974","journal-title":"Tetrahedron Lett."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"8101","DOI":"10.1021\/jp983286r","article-title":"Application of a General Rule to Induced Circular Dichroism of Naphthalene Derivatives Complexed with Cyclodextrins","volume":"102","author":"Kodaka","year":"1998","journal-title":"J. Phys. Chem. A"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"3702","DOI":"10.1021\/ja00062a040","article-title":"A general rule for circular dichroism induced by a chiral macrocycle","volume":"115","author":"Kodaka","year":"1993","journal-title":"J. Am. Chem. Soc."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"1687","DOI":"10.1021\/cr030052h","article-title":"Fluorescence of Organic Molecules in Chiral Recognition","volume":"104","author":"Pu","year":"2004","journal-title":"Chem. Rev."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"3313","DOI":"10.1021\/cr960144p","article-title":"Enantiomeric Recognition of Amine Compounds by Chiral Macrocyclic Receptors","volume":"97","author":"Zhang","year":"1997","journal-title":"Chem. Rev."},{"key":"ref_6","doi-asserted-by":"crossref","unstructured":"Khose, V.N., John, M.E., Pandey, A.D., Borovkov, V., and Karnik, A.V. (2018). Chiral Heterocycle-Based Receptors for Enantioselective Recognition. Symmetry, 10.","DOI":"10.3390\/sym10020034"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"460","DOI":"10.1021\/ja9818699","article-title":"An Efficient Catalyst for Asymmetric Epoxidation of Terminal Olefins","volume":"121","author":"Collman","year":"1999","journal-title":"J. Am. Chem. Soc."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"2801","DOI":"10.1039\/b305582e","article-title":"Novel chiral N4S2- and N6S3-donor macrocyclic ligands: Synthesis, protonation constants, metal-ion binding and asymmetric catalysis in the Henry reaction","volume":"1","author":"Gao","year":"2003","journal-title":"Org. Biomol. Chem."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"4490","DOI":"10.1021\/om0204641","article-title":"Asymmetric Cyclopropanation of Styrene Catalyzed by Chiral Macrocyclic Iron(II) Complexes","volume":"21","author":"Du","year":"2002","journal-title":"Organometallics"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"5786","DOI":"10.1021\/jo800533y","article-title":"Supramolecular Enantiodifferentiating Photocyclodimerization of 2-Anthracenecarboxylate Mediated by Capped \u03b3-Cyclodextrins: Critical Control of Enantioselectivity by Cap Rigidity","volume":"73","author":"Yang","year":"2008","journal-title":"J. Org. Chem."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"6916","DOI":"10.1021\/ja5032908","article-title":"Ammonia-Driven Chirality Inversion and Enhancement in Enantiodifferentiating Photocyclodimerization of 2-Anthracenecarboxylate Mediated by Diguanidino-\u03b3-cyclodextrin","volume":"136","author":"Yao","year":"2014","journal-title":"J. Am. Chem. Soc."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"3959","DOI":"10.1021\/jacs.7b12085","article-title":"Supramolecular Photochirogenesis Driven by Higher-Order Complexation: Enantiodifferentiating Photocyclodimerization of 2-Anthracenecarboxylate to Slipped Cyclodimers via a 2:2 Complex with \u03b2-Cyclodextrin","volume":"140","author":"Wei","year":"2018","journal-title":"J. Am. Chem. Soc."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"19357","DOI":"10.1039\/C8NJ04802A","article-title":"A pillar[5]arene-calix[4]pyrrole enantioselective receptor for mandelate anion recognition","volume":"42","author":"Lv","year":"2018","journal-title":"New J. Chem."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"15405","DOI":"10.1021\/jacs.6b07946","article-title":"Enhanced Triplet\u2013Triplet Energy Transfer and Upconversion Fluorescence through Host\u2013Guest Complexation","volume":"138","author":"Fan","year":"2016","journal-title":"J. Am. Chem. Soc."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"5022","DOI":"10.1021\/ja711260m","article-title":"para-Bridged Symmetrical Pillar[5]arenes: Their Lewis Acid Catalyzed Synthesis and Host\u2013Guest Property","volume":"130","author":"Ogoshi","year":"2008","journal-title":"J. Am. Chem. Soc."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"1017","DOI":"10.1016\/j.cclet.2016.04.021","article-title":"Enhanced head-to-head photodimers in the photocyclodimerization of anthracenecarboxylic acid with a cationic pillar[6]arene","volume":"27","author":"Gui","year":"2016","journal-title":"Chin. Chem. Lett."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"2028","DOI":"10.1039\/C8OB00156A","article-title":"Guest-regulated chirality switching of planar chiral pseudo[1]catenanes","volume":"16","author":"Yang","year":"2018","journal-title":"Org. Biomol. Chem."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"8269","DOI":"10.1002\/ange.201302675","article-title":"Solvent- and Achiral-Guest-Triggered Chiral Inversion in a Planar Chiral pseudo[1]Catenane","volume":"125","author":"Ogoshi","year":"2013","journal-title":"Angew. Chem."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"7590","DOI":"10.1038\/ncomms8590","article-title":"Mechanically selflocked chiral gemini-catenanes","volume":"6","author":"Li","year":"2015","journal-title":"Nat. Commun."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"6869","DOI":"10.1002\/anie.201702542","article-title":"Temperature-Driven Planar Chirality Switching of a Pillar[5]arene-Based Molecular Universal Joint","volume":"56","author":"Yao","year":"2017","journal-title":"Angew. Chem. Int. Ed."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"17436","DOI":"10.1021\/ja3082523","article-title":"Incorporation of an A1\/A2-Difunctionalized Pillar[5]arene into a Metal\u2013Organic Framework","volume":"134","author":"Strutt","year":"2012","journal-title":"J. Am. Chem. Soc."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"8782","DOI":"10.1039\/c3cc44672g","article-title":"Achiral guest-induced chiroptical changes of a planar-chiral pillar[5]arene containing one \u03c0-conjugated unit","volume":"49","author":"Ogoshi","year":"2013","journal-title":"Chem. Commun."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"1079","DOI":"10.1039\/c3ob42044b","article-title":"Dynamic self-inclusion behavior of pillar[5]arene-based pseudo[1]rotaxanes","volume":"12","author":"Guan","year":"2014","journal-title":"Org. Biomol. Chem."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"3877","DOI":"10.1021\/acs.joc.6b00617","article-title":"A1\/A2-Diamino-Substituted Pillar[5]arene-Based Acid\u2013Base-Responsive Host\u2013Guest System","volume":"81","author":"Hu","year":"2016","journal-title":"J. Org. Chem."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"14631","DOI":"10.1021\/ja0207302","article-title":"Enantioselective Formation of a Dynamic Hydrogen-Bonded Assembly Based on the Chiral Memory Concept","volume":"124","author":"Timmerman","year":"2002","journal-title":"J. Am. Chem. Soc."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"2643","DOI":"10.1039\/C8CC00840J","article-title":"Enhanced chiral recognition by \u03b3-cyclodextrin\u2013cucurbit [6] uril-cowheeled [4] pseudorotaxanes","volume":"54","author":"Dai","year":"2018","journal-title":"Chem. Commun."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"3430","DOI":"10.1021\/acs.joc.6b00130","article-title":"Inherently chiral azonia [6] helicene-modified \u03b2-cyclodextrin: Synthesis, characterization, and chirality sensing of underivatized amino acids in water","volume":"81","author":"Huang","year":"2016","journal-title":"J. Org. Chem."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"1680","DOI":"10.1021\/acs.orglett.8b00520","article-title":"Photocatalytic Supramolecular Enantiodifferentiating Dimerization of 2-Anthracenecarboxylic Acid through Triplet\u2013Triplet Annihilation","volume":"20","author":"Rao","year":"2018","journal-title":"Org. Lett."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"374","DOI":"10.1016\/j.jphotochem.2018.11.038","article-title":"Enhanced irregular photodimers and switched enantioselectivity by solvent and temperature in the photocyclodimerization of 2-anthracenecarboxylate with modified \u03b2-cyclodextrins","volume":"371","author":"Wei","year":"2019","journal-title":"J. Photochem. Photobiol. A Chem."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"898","DOI":"10.1021\/acs.orglett.7b00057","article-title":"Enantiodifferentiation in the photoisomerization of (z, z)-1, 3-cyclooctadiene in the cavity of \u03b3-cyclodextrin\u2013curcubit [6] uril-wheeled [4] rotaxanes with an encapsulated photosensitizer","volume":"19","author":"Yan","year":"2017","journal-title":"Org. Lett."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"4357","DOI":"10.1016\/j.tetlet.2007.04.104","article-title":"A remarkable stereoselectivity switching upon solid-state versus solution-phase enantiodifferentiating photocyclodimerization of 2-anthracenecarboxylic acid mediated by native and 3, 6-anhydro-\u03b3-cyclodextrins","volume":"48","author":"Yang","year":"2007","journal-title":"Tetrahedron Lett."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"5380","DOI":"10.1021\/acs.orglett.8b02297","article-title":"Umpolung of o-Hydroxyaryl Azomethine Ylides: Entry to Functionalized \u03b3-Aminobutyric Acid under Phosphine Catalysis","volume":"20","author":"Chen","year":"2018","journal-title":"Org. Lett."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"3156","DOI":"10.1039\/C9CC00097F","article-title":"Room-temperature phosphorescent \u03b3-cyclodextrin-cucurbit [6] uril-cowheeled [4] rotaxanes for specific sensing of tryptophan","volume":"55","author":"Yu","year":"2019","journal-title":"Chem. Commun."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"2178","DOI":"10.1021\/jo500054v","article-title":"Synthesis, Resolution, Structure, and Racemization of Inherently Chiral 1,3-Alternate Azacalix[4]pyrimidines: Quantification of Conformation Mobility","volume":"79","author":"Li","year":"2014","journal-title":"J. Org. Chem."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"3250","DOI":"10.1002\/chem.201505183","article-title":"Frozen Dissymmetric Cavities in Resorcinarene-Based Coordination Capsules","volume":"22","author":"Imamura","year":"2016","journal-title":"Chem. Eur. J."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"845","DOI":"10.1039\/c3nj01498c","article-title":"Selective recognition of \u201csolvent\u201d molecules in solution and the solid state by 1,4-dimethoxypillar[5]arene driven by attractive forces","volume":"38","author":"Tan","year":"2014","journal-title":"New J. Chem."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"9419","DOI":"10.1016\/j.tet.2012.09.006","article-title":"A facile, moisture-insensitive method for synthesis of pillar[5]arenes\u2014The solvent templation by halogen bonds","volume":"68","author":"Boinski","year":"2012","journal-title":"Tetrahedron"},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"707","DOI":"10.1016\/j.cclet.2013.05.008","article-title":"Selective binding of unsaturated aliphatic hydrocarbons by a pillar[5]arene","volume":"24","author":"Hu","year":"2013","journal-title":"Chin. Chem. Lett."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"1264","DOI":"10.1021\/ol200062j","article-title":"Planar-Chiral Macrocyclic Host Pillar[5]arene: No Rotation of Units and Isolation of Enantiomers by Introducing Bulky Substituents","volume":"13","author":"Ogoshi","year":"2011","journal-title":"Org. Lett."},{"key":"ref_40","unstructured":"Reichardt, C., and Welton, T. (2011). Solvents and Solvent Effects in Organic Chemistry, John Wiley & Sons. [4th ed.]."}],"container-title":["Symmetry"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2073-8994\/11\/6\/773\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T12:57:08Z","timestamp":1760187428000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2073-8994\/11\/6\/773"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2019,6,9]]},"references-count":40,"journal-issue":{"issue":"6","published-online":{"date-parts":[[2019,6]]}},"alternative-id":["sym11060773"],"URL":"https:\/\/doi.org\/10.3390\/sym11060773","relation":{},"ISSN":["2073-8994"],"issn-type":[{"type":"electronic","value":"2073-8994"}],"subject":[],"published":{"date-parts":[[2019,6,9]]}}}