High-Yielding, Regiospecific Synthesis of <i>cis</i>(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 <i>cis</i>(4,4′)-di(carbomethoxybenzo)-30-crown-10 (<b>1c</b>) is reported. The derived crown ether diol <b>1d</b> was converted to pyridyl cryptand <b>12</b> in 44% yield by reaction with pyridine-2,6-dicarbonyl chloride. Binding of two different 4,4′-bipyridinium (paraquat) species (<b>3</b>) and 2,2′-bipyridinium (diquat) <b>4</b> by <b>12</b> was explored via <sup>1</sup>H NMR spectroscopy, NOE experiments, mass spectrometry, X-ray crystallographic analyses, and isothermal titration calorimetry. Cryptand <b>12</b> exhibits the highest association constant for diquat ever reported (<i>K</i><sub>a</sub> = 1.9 × 10<sup>6</sup> M<sup>−1</sup>) and very high association constants for paraquats (<i>K</i><sub>a</sub> > 10<sup>5</sup> M<sup>−1</sup>) in acetone at 22 °C. The binding constant of diquat <b>4</b> by cryptand <b>12</b> is nearly 6-times higher than any other reported host.