A ‘building block’ approach to functionalized calix[4]pyrroles

Iodocalix[4]pyrrole 2 and trimethylsilylethynylcalix[4]pyrrole 3 are key intermediates en route to the preparation of the alkynyl-substituted calix[4]pyrrole system 4. This latter species, in turn, provides a versatile precursor that can be used to prepare a range of arylalkynyl-functionalized calix[4]pyrroles (viz., 5–9) by reacting with an appropriate aryl iodide under Sonogashira conditions (i.e., in the presence of tetrakis(triphenylphosphine)palladium(0)). Significant red-shifts in the λmax values and broadenings of the absorption peaks are seen in the UV–vis spectra of systems 6 and 7 upon addition of anions (e.g., F−, Cl−, H2PO4−) in CH2Cl2, a finding that leads to the suggestion that these or other analogous systems could find application as anion sensors.