Alkylation and Conformational Restriction in Calix[6]arene Derivatives: the Synthesis and Structure of 1,2,4,5-Tetrakis(ethoxycarbonylmethyl)-p-t-butylcalix[6]arene Benzene Disolvate

Abstract

Alkylation of p-t-butylcalix[6]arene with ethyl bromoacetate results in a mixture of product ethers from which a tetraether can most easily be isolated in moderate yield; this product exhibited a degree and pattern of substitution which were unexpected given the literature on reactions of this type. A room-temperature, single-crystal X-ray study shows the tetraether compound to be triclinic P^-1, a 16·375(5), b 14·296(9), c 10·29(2) Å, α 72·4(1), β 87·12(9), γ 72·22(4)°, Z = 1; conventional R on |F| was 0·095 for 2858 independent 'observed' reflections. The molecule is disposed about a crystallographic inversion centre and adopts a 1,2,3-alternate conformation distorted by different ethoxycarbonylmethyl substituent dispositions within the inversion-related halves. The benzene molecules occupy lattice sites between the calixarene molecules and are well removed from inclusion in the calixarene cavity, which is largely blocked by two of the ethoxycarbonylmethyl substituents.