Highly selective preparation of conformationally rigid stereoisomeric calix[4]arenes with two carboxymethoxy groups

Abstract

Highly selective formation of the 1,3-alternate and partial cone conformational isomers of p-tert-butylcalix[4]arene diesters 5 with two butoxy and two methoxycarbonylmethoxy groups was achieved by alkylations of disubstituted calix[4]arenes 3 and 4, respectively, with KH as the base in THF. The potassium diphenoxide form of 3 was shown by NMR spectroscopy to adopt a 1,3-alternate conformation which provides strong evidence for a template effect of potassium cations on the conformation of the calix[4]arene reactant. Alkylation with subsequent hydrolysis of the diesters provides an effective route for the preparation of the 1,3-alternate and partial cone isomers of p-tert-butylcalix[4]arenedicarboxylic acids 6.