Calixarenes 30. Calixquinones

Chlorine dioxide and thallium trifluoroacetate are shown to be useful reagents for the preparation of calixquinones. p-H-Calix4]arene( 1a ),p-H-calix5]arene ( 1b ), and p-H-calix6]arene ( 1c ) are oxidized in modest yields by ClO₂ to the fully quinonoid compounds calix4]tetraquinone ( 2a ), calix5]pentaquinone ( 2b ), and calix6]hexaquinone ( 2c ), respectively. Although Tl(OCOF₃)₃ is less effective for the oxidation of 1a-c , it proves to be the reagent of choice for converting partially etherified or esterified calixarenes carrying p-tert-butyl groups directly to partially quinonoid calixarenes. Thus, monosubstituted calix4]arenes yield triquinones; disubstituted calix4]arenes yield diquinones; trisubstituted calix4]arenes yield monquinones; and tetrasubstituted calix6]arenes yield diquinones. The structures of the calixquinones have been established by elemental analysis, ¹H NMR spectroscopy, mass spectroscopy, and in the case of 2c by X-ray crystallography. Since the starting materials are readily accessible, the calixquinones become easily available compounds for further study.