Influence of the hydrogen bond on the iteroselective O-alkylation of calix[4]resorcinarenes

Abstract

The effect of the hydrogen bond on the reactivity of hydroxyl groups of tetra( p -hydroxyphenyl)calix[4]resorcinarene with glycidyl methacrylate was studied. When the O -alkylation reaction was carried out with tetra( p -methoxyphenyl)calix[4]resorcinarene, the exposed hydroxyl groups of the upper rim did not react in the presence of NaOH or pyridine. When the O -alkylation reaction of tetra( p -hydroxyphenyl)calix[4]resorcinarene was carried out in the presence of NaOH, the expected tetraalkylation product in the lower rim was obtained, whereas the monoalkylation product in the lower rim was obtained, when the reaction was carried out with pyridine as base. Spectroscopic evidence showed that the reaction is selective for one hydroxyl group in the lower rim without affecting the hydroxyl groups in the upper rim. Suitable crystals of tetra( p -hidroxyphenyl)calix[4]resorcinarene in DMSO were obtained from the reaction and were characterized through an X-ray crystal structure determination and showed that asymmetric unit contains eight molecules of DMSO, and analysis indicated that calix[4]resorcinarene prefers a chair configuration in the solid state. In the crystal array, classical hydrogen bond O–H⋯O interactions and intermolecular contacts were observed. The formation of these crystals confirms the low reactivity of this conformer in the process. • O -Alkylation is regioselective. • Crown conformer is reactive. • Resorcinarene in chair conformation does not react.