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Abstract: An intriguing reaction of 4-hydroxycoumarins with 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) occurred in the presence of catalytic acetic acid in ethanol at reflux with the products being obtained in high yields. [Copyright &y& Elsevier]

Abstract: The strategy of bridging the anisole units at the upper rim of calix[6]arene has been applied to strain the conformations of calix[6]arene. Based on the selective formylation of the 1,3,5-tri-p-tert-butylcalix[6]arene, several new calix[6]arene derivatives with different 1,3-bridged chains or a 1,3,5-tripod bridge at the upper rim have been prepared with moderate yields. The 1H NMR spectra indicate that these calix[6]arene derivatives adopt a cone conformation, which has also been confirmed by the theoretical calculation at AM1 level. X-ray crystal structure of 1,3,5-tripod bridged compound 5 discloses that the calix[6]arene host stands in a cone conformation with approximate C 3v symmetry, and that a methanol molecule is enclosed in its hydrophobic cavity and stabilized by multi hydrogen bonds. [Copyright &y& Elsevier]