Formation of calix[4]arenes with acyloxycarboxylate functions

Calix[4]arenes are an exciting class of multifunctional compounds. Their ability to bind small molecules and ions actively make them useful tools in many scopes of application. While looking for a suitable chelating agent, a particular modification of the calix[4]arene lead to an unexpected side reaction. In this work, we will describe the selective formation of the observed acyloxy-acetate derivatives, which can be tuned by the choice of wet solvents. This side reaction is not described in the literature so far. All new compound were obtained in yields >45% and fully characterized by NMR, MS, and X-ray crystallography. Using the monomeric derivatives of calixarenes and X-ray data, an explanation for the reaction mechanism was postulated. Further, we report on different reaction conditions that were investigated to verify and elaborate this type of reaction. Finally, two additional derivatives of this class were synthesized according to this mechanism to support our considerations.