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

7,15,23-Tri-tert-butyl-25,26,27-trihydroxy-2,3,10,11,18,19-hexahomo-3,11,19-trioxacalix[3]arene (1H₃) 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 (1R₃) 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 1Me₃, 1Et₃, and 1Pr₃ whereas it is inhibited for 1Bu₃, (ii) the cone/partial-cone equilibrium in 1Et₃ and 1Pr₃ is predominantly inclined to partial-cone, indicating the thermodynamic stability of partial-cone conformers, and (iii) in the product distribution of 1Bu₃ 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-1Bu₃ are discussed. 1R₃ showed the selectivity toward K⁺ among alkali metal cations and the cone conformers had the extractability (Ex%) higher than the partial-cone conformers. Cone-1R₃ showed the high affinity for BuNH₃⁺ because of (averaged) C₃ symmetry common to both cone-1R₃ host and BuNH₃⁺ guest.