High-Yielding, Regiospecific Synthesis of cis(4,4′)-Di(carbomethoxybenzo)-30-crown-10, Its Conversion to a Pyridyl Cryptand and Strong Complexation of 2,2′- and 4,4′-Bipyridinium Derivatives

A high yielding (93%), regiospecific synthesis of cis(4,4′)-di(carbomethoxybenzo)-30-crown-10 (1c) is reported. The derived crown ether diol 1d was converted to pyridyl cryptand 12 in 44% yield by reaction with pyridine-2,6-dicarbonyl chloride. Binding of two different 4,4′-bipyridinium (paraquat) species (3) and 2,2′-bipyridinium (diquat) 4 by 12 was explored via ¹H NMR spectroscopy, NOE experiments, mass spectrometry, X-ray crystallographic analyses, and isothermal titration calorimetry. Cryptand 12 exhibits the highest association constant for diquat ever reported (K_a = 1.9 × 10⁶ M⁻¹) and very high association constants for paraquats (K_a > 10⁵ M⁻¹) in acetone at 22 °C. The binding constant of diquat 4 by cryptand 12 is nearly 6-times higher than any other reported host.