Propeller substituents imposing steric restraint on crown ethers

Abstract

Crown ethers with steric restraint imposed by a three-bladed propeller substituent have been synthesized and the X-Ray crystal structures of one example and its NaNCS complex indicate approximately the same conformation of the propeller but quite different conformations of the ether ring in the two; n.m.r. solution spectra indicate that the flipping of the propeller and of the crown moieties are mutually restricted in these crown ethers.