Post‐Synthetic Modification of Calix[4]arene Framework by Iridium–Mediated Alkyne Insertion into an Inert C−C Bond: A Novel Strategy for Unsymmetrical Macrocycles

Abstract

AbstractAs a novel synthetic method for unsymmetrical macrocycles, we herein developed a post‐synthetic modification of calix[4]arenes by insertion of a terminal alkyne into an inert C(methylene)−C(aryl) bond of the macrocyclic framework. In this transformation, C‐iridated calix[4]arenes, readily synthesized through C−H bond activation of the parent calix[4]arene, undergoes C(methylene)−C(aryl) bond cleavage followed by insertion of an alkyne to provide a ring‐expanded calix[4]arene complex. Removal of the iridium metal from the resulting complex was readily accomplished by a simple treatment with an acid. The developed sequential method affords novel unsymmetrical, monofunctionalized macrocyclic compounds via 3 steps from the parent calix[4]arene in good yield. The unique unsymmetrical structures of the alkyne–inserted macrocycles were evaluated by X‐ray single crystal analyses. On the basis of theoretical calculations, we propose a reaction mechanism involving an uncommon C−C bond cleavage step through δ‐carbon elimination for the ring enlargement process.