Calix[4]arenes bridged at the lower rim

Abstract

Calix[41 arenes, in which two opposite p-positions are linked by an aliphatic chain, and their derivatives show transport or complexation properties strongly dependent on the length of this chain. Bicyclo-calix[4]arenes, a special case of 1,3-bridged calix[41 arenes, and annelated calix[41 arenes, a special case of 1 ,&bridged calix [4] arenes, are also described. Although the preferred conformation of calix[4]arenes is the coneconformation due to its stabilization by a cyclic array of hydrogen bonds between the phenolic hydroxyl goups, these molecules are flexible, with a cone to cone inversion rate of about 150 8-1 for a calix[glarene at 47OC (ref. 1). The cone (or any other) conformation may be fixed by derivatisation of the phenolic oxygens. Another possibility is, to connect two p-positions of opposite (1) or adjacent (3) phenolic units by a suitable bridge. Although partial cone or alternate conformations still are possible in these compounds, the complete ring inversion is entirely prevented by the bridge. Compounds of type 1 with (CH2 In -bridges are available by reaction of suitable diphenols with bisbromomethylated phenols in dioxane in the presence of Tic14 (ref. 2).