Intramolecular Ar-O-Ar bond formation in calixarenes

The formal dehydration of two vicinal phenol moieties of p-tert-butylcalix [6] arene was achieved in two steps by mild oxidation of the calixarene fol lowed by treatment of the resulting monospirodienone derivative (9c) with a n ionic hydrogenation mixture (Et3SiH/CF3COOH). Reaction of 9c yielded the unsubstituted xanthenocalix[6]arene 11d, while treatment of the monospirodi enone derivative of a spherand-type calixarene (13) with Et3SiH/CF3COOH aff orded the dibenzofuran derivative 15. The formation of the latter product i ndicates that, at least for 13, the rings forming the Ar-O-Ar bond in the p roduct are not those connected by the spiro bond in the starting material. Methylation of the phenolic hydroxyl groups of 11d with methyl p-toluenesul fonate/K2CO3 or dimethyl sulfate/base afforded its dimethyl and tetramethyl ether derivatives. The parent xanthone calix[6]arene derivative 17b was pr epared by O-methylation of the phenol groups followed by CrO3 oxidation of the xanthene methylene group and deprotection of the OH groups. McMurry cou pling of calixanthone 17a afforded the dixanthylene 18. Calixarenes 11d and 15 (which possess a xanthene and dibenzofuran group, respectively) were st ructurally characterized by X-ray crystallography.