Abstract:The synthesis and properties of a number of functionalized calix[4]pyrroles are described. To date, two generalized preparative approaches have been pursued. The first involves modifying the basic pyrrole-plus-ketone synthesis of calix[4]pyrrole by using modified precursors or by co-condensing more than one ketone with pyrrole. The second approach relies on the reaction of a pre-formed calix[4]pyrrole with an electrophile. In both cases, the resulting species can be subject to further manipulation. In this way a range of structures, including ones bearing ancillary recognition subunits, electro-or photochemical reporter groups, and/or water solubilizing substituents may be obtained. Solid supports bearing calix[4]pyrroles may also be produced in this way.

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In this Communication, a new approach to enhancing the efficacy of liquid-liquid anion exchange is demonstrated. It involves the concurrent use of appropriately chosen hydrogen-bond-donating (HBD) anion receptors in combination with a traditional quaternary ammonium extractant. The fluorinated calixpyrroles 1 and 2 and the tetraamide macrocycle 4 were found to be particularly effective receptors. Specifically, their use allowed the extraction of sulfate by tricaprylmethylammonium nitrate to be effected in the presence of excess nitrate. As such, the present work provides a rare demonstration of overcoming the Hofmeister bias in a competitive environment and the first to the authors’ knowledge wherein this difficult-to-achieve objective is attained using a neutral HBD-based anion binding agent under conditions of solvent extraction.