Optically Pure Calix[6]tris-ammoniums:  Syntheses and Host−Guest Properties toward Neutral Guests

• Published in: Journal of organic chemistry Vol. 70; no. 25; pp. 10552 - 10560
• Main Authors: Darbost, Ulrich, Zeng, Xianshun, Giorgi, Michel, Jabin, Ivan
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 09.12.2005; Amer Chemical Soc
• Subjects: Alicyclic compounds; Alicyclic compounds, terpenoids, prostaglandins, steroids; Calixarenes - chemical synthesis; Calixarenes - chemistry; Chemistry; Chemistry, Organic; Exact sciences and technology; Magnetic Resonance Spectroscopy; Molecular Conformation; Organic chemistry; Phenols - chemical synthesis; Phenols - chemistry; Physical Sciences; Preparations and properties; Quaternary Ammonium Compounds; Science & Technology; CHIRAL RECOGNITION; LIGANDS; FLUORESCENCE; X-RAY; RECEPTOR; BEARING; BINDING; DERIVATIVES; COMPLEXATION; CALIXARENES; Neutral medium; Calixarene; Inclusion compound; Chemical synthesis; Ammonium compound
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo051886y

Optically pure calix[6]arenes bearing chiral amino arms 4, 7, and 10 have been synthesized in high yields from the known symmetrically 1,3,5-trismethylated calix[6]arene. For both compounds 7 and 10, the key step consists of an efficient selective alkylation on the narrow rim of the calix[6]arene with Ba(OH)2 as the base. All of these chiral calix[6]tris-amines possess a similar flattened cone conformation with the cavity occupied by the methoxy groups. In contrast to 4 and 7, upon protonation, the enantiopure calix[6]arene 10 can switch to the opposite flattened cone conformation through self-assembly of its ammonium arms in an ion-paired cap which closes the cavity. As shown by NMR host−guest studies and an X-ray structure, the obtained polarized host (10 · 3H + ) behaves as a remarkable endo-receptor for small polar neutral molecules. Thanks to the tris-cationic chiral binding site of 10 · 3H + , it was shown that the guests experience a chiral environment upon inclusion. Finally, the first example of enantioselective molecular recognition inside the cavity of a calix[6]arene has been evidenced with a racemic 1,2-diol guest.