Synthesis and complexation study of calix[4]arene containing stilbene and crown ether

Abstract

A series of stilbene-bridged calix[4]arenes were synthesized in high yields through an intramolecular reductive McMurry coupling of bisbenzaldehyde calix[4]arene using high dilution condition and a large excess of TiCL[subscript4] . Tetra- and pentaethylene glycol chains were tethered to the opposite phenolic groups of calix[4]arene to form stilbene-bridged calix[4]arene crown-5 and crown-6 respectively. The presence of stilbene bridge over the calix[4]arene rim effectively prevents the connection of the polyether chains in the cone conformation resulting in the exclusive formation of 1,3 alternate stilbene-bridged calix[4]arene crown product. Comparing to the cone conformation, the 1.3 alternate calix[4]arene crown ethers have greater extractability and selectivity toward Cs[superscript+] . The attempts to construct the crown ethers for trans-isomer of m-stilbene-bridged calix[4]arene from m-trans-stilbene-bridged calix[4]arene have not been successful, yielding only intractable meterials. Extensive conformation analyses and synthesis of non crown analogues revealed that the length of m-trans-stilbene-bridge is so long that force calix[4]arene into a pinched cone conformation in which the hydroxyl rim is too narrow to allow that phenyl ring flip. The results from this work provide a very logical and reliable insight for the synthesis of cone, pinched cone, partial cone and 1,3-altenate calix[4]arene derivatives.