Conformational Restriction of the Calix[6]arene Macrocycle by the Ritter Reaction

• Published in: European Journal of Organic Chemistry Vol. 2006; no. 2; pp. 522 - 530
• Main Authors: Vatsouro, Ivan M., Shokova, Elvira A., Shestakova, Alla K., Chertkov, Vyacheslav A., Kovalev, Vladimir V.
• Format: Book Review Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01-01-2006; WILEY‐VCH Verlag
• Subjects: Adamantane; Amides; Calixarenes; Conformation analysis; Regioselectivity
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.200500604

Herein we report on the development of a novel and efficient approach to the restriction of the conformational mobility of calix[6]arenes. The method involves the addition of tertiary alcohols to calix[6]arenes with one, three and six cyanomethoxy groups attached to the lower rim under modified Ritter reaction conditions. Alkylation of monocyanomethoxy‐p‐tert‐butylcalix[6]arene (1) and 37,39,41‐trimethoxy‐38,40,42‐tricyanomethoxy‐p‐tert‐butylcalix[6]arene (2) with 3‐R‐1‐adamantanols (R = H, CH2COOH) in trifluoroacetic acid afforded the corresponding mono‐ and triamides with cone‐like conformations. The partial alkylation of hexanitrile derivatives showed unexpected regioselectivity. Addition of 1‐adamantanol or tert‐butyl alcohol to hexacyanomethoxy‐p‐X‐calix[6]arenes 3a–c (X = tert‐butyl, 1‐adamantyl, 3‐methoxycarbonylmethyl‐1‐adamantyl) gave 37,40‐dinitrile‐38,39,41,42‐tetraamides as the major products. These tetraamides are conformationally restricted in solution over a wide range of temperatures and adopt a flattened 1,2,3‐alternate conformation, as shown by 2D and variable‐temperature NMR experiments. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)