Exploring Sulphonated Calix[n]arenes as Catalysts in Organic Reactions

Abstract

Catalysis plays a crucial role in modern chemistry, with macrocyclic compounds like calixarenes serving as key players in organic transformations through supramolecular chemistry. These macrocycles, synthesized from phenol and formaldehyde condensation, exhibit a variety of conformations, such as cone and partial-cone, due to their flexible structures. Their effectiveness as catalysts arises from their lipophilic cavities and the ease of functionalization on both the upper and lower rims. Water-soluble calixarenes, in particular, have gained attention for their ability to interact with hydrophobic cavities, facilitating molecular recognition in aqueous environments. A landmark achievement in this field was Shinkai's synthesis of water-soluble calix[4]arene in 1984, which involved sulphonation using tert-butyl groups, resulting in compounds known for their low toxicity and encapsulation capabilities. This review provides a comprehensive overview of the advancements in sulphonated calixarenes as catalysts, emphasizing their diverse applications and potential for future development. Key catalytic reactions and their substrate scopes are discussed, along with future perspectives on how these compounds can further revolutionize catalytic processes.