The calix[4]pyrroles are a class of old but new heterocalixarene analo
gues that show interesting anion and neutral substrate binding propert
ies. Calix[4]pyrroles are easy to make and functionalize. As such,they
have been employed in the production of separation media for anionic
and neutral species. Calixpyrroles also provide useful precursors for
the generation of novel calixpyridinopyrroles and calixpyridines.