Treatment of p-t-butylcalix[4]arene with bromoacetone–potassium carbonate yields a crystalline tetraketone which shows exceptionally high phase-transfer activity towards alkali metal cations in aqueous solutions; X-ray and n.m.r. analyses show that the receptor possesses a cone conformation in which the carbonyl groups are pre-organised for ion binding.
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Ferguson et al. (1987) studied this question.