Clean, efficient syntheses of cyclotriveratrylene (CTV) and tris-(O-allyl)CTV in an ionic liquid

Abstract

Cyclic cyclotriveratrylene (CTV) type supramolecular host compounds are traditionally synthesized under harsh dehydrating conditions and require the use of large quantities of organic solvent in the reaction workup. We now report both solvent-free and ionic liquid reaction media in efficient ‘green’ syntheses of CTVs under mild conditions. The ionic liquid tributylhexylammonium bis(trifluoromethylsulfonyl)amide (N₆₄₄₄ Imide) provides a safe, non-volatile reaction medium that is readily recycled. This methodology obviates the need for the use of large quantities of organic solvent and strong dehydrating acids yet provides pure crystalline product in high yields. Unlike most traditional synthetic routes to these compounds extensive recrystallisation or chromatographic steps are avoided and the molten salt reaction medium is readily recovered. Interestingly, condensation also occurs under ambient conditions on grinding of solid benzyl alcohol monomers with a suitable solid acid to afford the corresponding CTV. Ionic liquids have, as yet, been little explored as reaction media or solvents yet these offer significant advantages over volatile (and often toxic) organic solvents. Human exposure to potentially harmful vapours is obviated and recycling of the ionic liquid reaction medium significantly reduces waste generated. The procedures described here serve to extend the use of ionic liquids as reaction media.