SYNTHESIS AND COMPLEXATION STUDIES OF REGIOISOMERS AND CONFORMATIONALISOMERS OF P-TERT-BUTYLCALIX[4]ARENE BEARING PYRIDINE OR PYRIDINE N-OXIDE PENDANT GROUPS AT THE LOWER RIM

Selected title compounds have been prepared in order to provide calix[ 4]arene ligands having different shapes of the calix[4]arene skeleton (cone, partial cone, 1,2-alternate, or 1,3-alternate) and spacial arra ngements (syn-proximal, syn-distal, or anti-distal) of pendant pyridin e or pyridine N-oxide binding groups. The structure of 1,2-alternate t etrakis[(2-pyridylmethyl)oxy]calix[4]arene 9, obtained in low yield by direct alkylation of the parent p-tert-butylcalix[4]arene 1 with PicC l . HCl and Cs2CO3, has been elucidated by single crystal X-ray analys is. N-Oxide derivatives have been obtained in good yield by m-CPBA oxi dation of the appropriate pyridinocalix[4]arene precursors in dry Et(2 )O or THF. The H-1 and C-13 NMR spectral changes upon N-oxide formatio n are discussed. Extraction studies with alkali metal picrates from an aqueous solution into CH2Cl2 have shown that the ionophoric efficienc y is low. The highest phase-transfer values are observed for cone tetr apyridinocalix[4]arene 7 (selectivity follows the order Na+ > K+ > Rb > Cs+ > Li+), whereas the corresponding N-oxide 7a has no activity. H owever, NMR complexation studies with Na+ and K+, while confirming a l ow complexation rate, indicate that in aprotic solvents tetra-N-oxide derivative 7a is a good complexer having a faster kinetic than its pyr idino precursor 7.