Chemistry of crown ethers: Synthesis of crown ethers based on α,β-bis(halomethyl)- or α,β-bis(hydroxymethyl)-substituted aromatics

Abstract

Two types of novel crown ethers in which a polyether chain is linked, via C atoms, with two adjacent C atoms of an aromatic or heteroaromatic ring have been synthesized by reaction of α,β-bis(halomethyl)-substituted aromatics with polyethylene glycolates. Both 1:1 and 2:2 cyclic reaction products were formed, in yields varying from 1 to 53% and from 0 to 24%, respectively. The relatively high yields of these macrocyclic polyethers (rings containing from 11 to 34 atoms), obtained without operating at high dilution, depend both on the chain length of the glycol and on the nature of the cation. This can be explained in terms of a “template” effect of the cation in the cyclization step. Experimental evidence supporting such an effect was obtained from the relationship between the 1:1 product selectivity and the glycol chain length for cations with different ionic radii (L +, Na + and K +). Furthermore, a correlation has been established between the ratio of the yields of 1:1 and 2:2 cyclic products from the reaction of 1,2-bis(bromomethyl)benzene and dipotassium triethylene glycolate and the ratio of the relative complexation constants of these compounds with potassium salts.