Controlling Factors in the Synthesis of Cucurbituril and Its Homologues

The acid-catalyzed synthesis of cucurbitnurils from formaldehyde and glycoluril is poorly understood. In this paper, we examine a wide range of reaction conditions that include the effects of acid type, acid concentration, reactant concentrations, and temperature to both probe the mechanism and optimize the yields of isolated cucurbitnurils, where n = 5-10. A mechanism for the formation of these cucurbitnurils is presented. Individual cucurbitnurils were unambiguously identified in reaction mixtures using ESMS and (13)C NMR.