FUNCTIONALIZATION OF P-TERT-BUTYLCALIX[5]ARENE BY ALKYLATION WITH 2-(CHLOROMETHYL)PYRIDINE HYDROCHLORIDE

A study of the base-catalyzed alkylation of p-tert-butylcalix[5]arene (1) with 2-(chloromethyl)pyridine hydrochloride (PicCl . HCl) in DMF h as led to the isolation and identification of the 7 possible pyridinyl homologues of 1 in the cone conformation. Reactions of 1 with limitin g amounts of alkylating agent (2 to 4 equiv) and base (CsF, KHCO3, BaO /Ba(OH)(2), K2CO3, NaH) produced invariably complex mixtures, which we re separated into the pure components by chromatographic means. Regios elective 1,2,4- or 1,2,3-tri-O-alkylation has been achieved in moderat e yield (21-22%) by an appropriate choice of molar ratios, solvent, an d base. Pentaethers 8-10, endowed with 2-pyridinyl, 3-pyridinyl, and 2 -quinolylmethyl pendant groups at the lower rim, respectively, have be en also prepared in good yield. The cone conformation in solution for all new compounds has been established by NMR spectroscopy and confirm ed for 1,2,3-tri-O-alkylated 5 by a single-crystal X-ray analysis. In the solid state the cone conformation of 5 is mainly determined by the presence of intramolecular hydrogen bonds between adjacent phenolic o xygens, and between the phenolic oxygen and the proximal pyridinyl nit rogen.