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

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Abstract
The synthesis of a N-confused calix[4]pyrrole-α-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 system.