5,10-Diacylcalix[4]pyrroles: synthesis and anion binding studies.

5,10-Diacylcalix[4]pyrrole, a new positional isomer of the recently reported 5,15-diacylcalix[4]pyrrole, is synthesized as its two configurational isomers by acid catalysed condensation of meso-diacyltripyrrane with pyrrole. The solution phase anion binding of the two isomers of 5,10-diacylcalix[4]pyrrole was investigated by (1)H NMR spectroscopy in chloroform-d and isothermal titration calorimetry (ITC) in acetonitrile to gain insights into the positional and conformational effects of substituents on the macrocycle periphery towards anion binding. During the investigation, a functionalized, stable pyrrole-2-carbinol was isolated and subsequently converted to the corresponding tripyrrane in situ.