Functionalization of Bambusurils by a thiol-ene click reaction and a facile method for the preparation of anion-free Bambus[6]urils

Abstract : New sulfide‐functionalized bambus[4]urils ((RS)$_8$BU[4]) and bambus[6]urils ((RS)$_{12}$BU[6]) have been synthesized through thiol‐ene click coupling reactions (TEC) of allylbambus[n]urils. 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 AgSbF$_6$ to prepare anion‐free BU[6]. NMR methods were used to estimate association constants of these new empty BU[6] with different anions. Quantum chemistry calculations were employed to rationalize the observed results. These new functionalized bambusuril scaffolds in alternate conformation could find applications as multivalent binders.