Functionalization of Bambusurils by a Thiol-Ene Click Reaction and a Facile Method for the Preparation of Anion-Free Bambus[6]urils

Sulfide-functionalized bambus[4]urils ((RS)(8)BU[4]) and bambus[6]urils ((RS)(12)BU[6]) were synthesized through thiol-ene click coupling reactions (TEC) of allylbambus[n]urils. Thiosugars were grafted to BU[4] and BU[6]. Synthesis of BU[6] derivatives always requires the use of a template anion (iodide, chloride, or bromide), which is enclosed in the cavity of BU[6]. We show that this anion influences the reactivity of bambus[6]urils. An encapsulated iodide makes allyl functions of allyl(12)BU[6] less reactive towards TEC and hydrogenation reactions in comparison to the corresponding chloride or bromide inclusion complexes. This is critical for the chemical reactivity of BU[6] and even more to determine their anion-binding properties. We report a new, facile and fast method using AgSbF6 to prepare anion-free BU[6]. NMR spectroscopic methods were used to estimate association constants of these new empty BU[6] with different anions. Quantum chemical calculations were employed to rationalize the observed results. These new functionalized bambusuril scaffolds in alternate conformations could find applications as multivalent binders.