ON THE OCCURRENCE OF THE 1,3,5-TRISUBSTITUTION PATTERN IN THE O-ALKYLATION OF P-TERT-BUTYLCALIX[6]ARENE

1,3,5-Trisubstitution at the phenolic hydroxyls of p-tert-butylcalix[6]arene (1), previously obtained in sizeable yield only with Mel (Casnati ct al. J. Chem. Sec., Chem. Commun. 1991, 1413), has been now achieved by direct O-alkylation with alkyl iodides (Et, n-Pr, n-Bu) and p-X-benzyl bromides, (X = tert-Bu, Me, Br, NO2) in the presence of a weak base (K2CO3 or CsF). These results suggest that 1,3,5-trisubstitution can also be extended to other alkylating agents provided that an appropriate weak base is used. The 1,3,5-tris(p-X-benzyl) ethers 6-9, whose structure have been established by H-1-NMR spectral analysis and chemical correlation, in CDCl3 solution adopt a conformation with only a 2-fold symmetry element bisecting two aromatic rings.