Electrochemical study of two tris-O-substituted calix[4]arenes: 25,27-Dipropoxy-26-hydroxy-28-benzoyloxycalix[4]arene(partial cone) and 25,27-dibenzyl-26-hydroxy-28-benzoyloxy-calix[4]arene(partial cone). Electrosynthesis of the corresponding calix[4]arene-monoquinones

Abstract

The anodic oxidation of 25,27-dipropoxy-26-hydroxy-28-benzoyloxycalix[4]arene 1 and 25,27-dibenzyl-26-hydroxy-28-benzoyloxy-calix[4]arene 2 in dichloromethane was investigated by electrochemical and spectroelectrochemical techniques. For both, the overall reaction is a two-electron oxidation of the phenolic group according to an ECE mechanism resulting in the ultimate formation of an observable phenoxylium cation. After reaction of the latter with traces of water and subsequent internal electron transfer, the corresponding calix[4]-monoquinones are formed.

Electrosynthesis and Structural Studies of 5,17-Di-tert-butyl-26,28-dimethoxycalix[4]arene-25,27-diquinone

“…Calix [4]arenediquinone adopts a partial cone conformation ( Fig. 2) with two rings almost parallel to the main axis of calixarenes, while one arene is rotated by approximately 180˚ and the last ring highly tilted with respect to this axis.…”

“…2) with two rings almost parallel to the main axis of calixarenes, while one arene is rotated by approximately 180˚ and the last ring highly tilted with respect to this axis. The crystal structure showed that this compound crystallizes as a solvate with CH2Cl2 molecules embedded in pairs of calix [4]arenediquinone, which define a cavity (Fig. 3a).…”

“…Preparative oxidation of the calix [4]arene derivative in an acetonitrile solution leads to its corresponding calix [4]arenemonoquinone and calix [4]arenediquinone. 5,17-Di-tert-butyl-26,28-dimethoxycalix [4]arene-25,27-diquinone crystallizes from CH2Cl2 in monoclinic space group P21/a with a = 15.7058 (6) After a consumption of 6 electrons per molecule, the solvent was removed under a vacuum, and a crude oxidation mixture was extracted with diethylether. The ether solution was filtered and evaporated.…”

“…The structure of 5,17-di-tert-butyl-26,28-dimethoxycalix [4]arene-25,27-diquinone, obtained by controlled potential electrolysis on a platinum electrode of 5,11,17,23-tetra-tert-butyl-26,28-dimethoxycalix [4]arene-25,27-diol, was determined by an X-ray diffraction method. Preparative oxidation of the calix [4]arene derivative in an acetonitrile solution leads to its corresponding calix [4]arenemonoquinone and calix [4]arenediquinone.…”

“…The ether solution was filtered and evaporated. Calix [4]arenediquinone (yield = 68%) was separated by chromatography on silica gel with a mixture of dichloromethane-acetone (90/10, v,v) as eluent.…”