Conformational isomerism in and binding properties to alkali-metals and an ammonium salt of O-alkylated homooxacalix[3]arenes.

Abstract

7,15,23-Tri- tert-butyl-25,26,27-trihydroxy-2,3,10,11,18,19-hexahomo-3,11,19-trioxacalix[3]arene ( 1H 3) was tri- O-alkylated with alkyl halides (RX: R=Me, Et, n-Pr, and n-Bu) in the presence of various bases and the products ( 1R 3) were analyzed by HPLC and 1H NMR spectroscopy. It was found that (i) ring inversion which occurs through the oxygen-through-the-annulus rotation is allowed for 1Me 3, 1Et 3, and 1Pr 3 whereas it is inhibited for 1Bu 3, (ii) the cone/partial-cone equilibrium in 1Et 3 and 1Pr 3 is predominantly inclined to partial-cone, indicating the thermodynamic stability of partial-cone conformers, and (iii) in the product distribution of 1Bu 3 partial-cone is yielded in preference for cone, indicating the kinetic preference for partial-cone. From the analysis of the reaction intermediates the possible reaction routes to cone- and partial-cone- 1Bu 3 are discussed. 1R 3 showed the selectivity toward K + among alkali metal cations and the cone conformers had the extractability (Ex%) higher than the partial-cone conformers. Cone- 1R 3 showed the high affinity for BuNH 3 + because of (averaged) C 3 symmetry common to both cone- 1R 3 host and BuNH 3 + guest.