A facile, moisture-insensitive method for synthesis of pillar[5]arenes—the solvent templation by halogen bonds

A new, very efficient, and selective preparation method of peralkylated pillar[5]arenes is presented. By replacing typical Lewis acids with trifluoroacetic acid (TFA) we were able to eliminate the need of anhydrous conditions without a loss of effectiveness. The method is highly practical: a) it is moisture-insensitive, b) starting from simple and cheap reagents and reactants, and c) allows for chromatography-free isolation of the products. The results indicate that the interactions with solvent molecules can modulate stability of the products and influence the reaction outcome. Dichloromethane (DCM) and dichloroethane (DCE) are complexed within the cyclopentamer cavity with association constants of 120 M−1 and 600 M−1, respectively (CDCl3). The interactions involve a combination of hydrogen–pi and halogen–pi bonds.