Anion recognition by N-confused calix[4]pyrrole-alpha-carbaldehyde and its Knoevenagel reaction derivatives

The synthesis of a N-confused calix[4]pyrrole--carbaldehyde is reported, together with its Knoevenagel reaction derivatives. The X-ray crystal structure of the aldehyde and two derivatives are reported showing the macrocycles adopting confused 1,3-alternate conformations in all cases. The affinity of these macrocycles for a range of anionic guests has been measured in DMSO-d6/0.5% water, and the results compared with the parent N-confused calix[4]pyrrole parent macrocycle. These studies show that the derivatives have a significantly higher affinity for anionic guests than the parent syste