Atropisomerism in 1,5-Bridged Calix[8]arenes

The first example of two discrete calix[8]arene conformational isomers, has been obtained by exhaustive benzylation of 1,5-tetramethylene-bridged calix[8]arene. It is demonstrated, with the aid of X-ray cristallography, that these atropisomers have two 3/4-cone halves oriented syn or anti with respect to the bridge/bridgeheads moiety. VT NMR studies indicate that the tert-butyl-through-the-annulus inversion is inhibited, while groups larger than n-hexyl or benzyl are required for curtailing the O-through-the- annulus route.