Recent Advancements in Calix[4]pyrrole-Based Anion-Receptor Chemistry

Calix[4]pyrroles and their congeners are conformationally flexible, nonplanar tetrapyrrolic macrocycles that can recognize anionic substrates. Although the mother calix[4]pyrrole was reported more than 100 years ago, anion recognition accompanied with conformational changes was first discovered in 1996. These compounds have shown preferential binding of halide anions such as fluoride and chloride as well as that of phosphate and carboxylate anions. Extensive efforts have been made to improve the affinity and selectivity. Continuous expansion of related research makes this easy-to-make macrocycle more promising. In this review, recent synthetic developments and the anion binding properties of newly developed calix[4]pyrroles are discussed and accomplishments to date are summarized. We hope that this review provides a seed for future developments in this area of chemistry.