Concave reagents. Part 27.1 Steric requirements of intraannular substituents in A,D-bridged calix[6]arenes

Abstract

A series of A,D-m-xylylene bridged calix[6]arenes 5 carrying substituents of different size in 2-position of the bridge have been investigated by dynamic NMR spectroscopy and by force field methods. Molecular mechanics calculations indicate a bean shaped conformation as the global energy minimum in which the calixarene scaffold adopts a half-pinched/half-winged arrangement.