title: Hexameric resorcinarene capsule is a Brønsted acid: investigation and application to synthesis and catalysis.
abstract: Molecular capsules have attracted interest as simple enzyme mimetics and several examples of catalytic transformations in water-soluble metal-ligand based systems have been reported. This is not the case for hydrogen-bond based molecular capsules, which in contrast can be employed in organic solvents. We describe herein our investigations of such a system: The resorcin[4]arene hexamer is one of the largest hydrogen bond-based self-assembled capsules and has been studied intensively due to its ready availability. We present evidence that the capsule acts as a reasonably strong Brønsted acid (pKa approximately 5.5-6). This finding explains the capsule's high affinity toward tertiary amines that are protonated and therefore encounter cation-π interactions inside the cavity. We were able to translate this finding into a first synthetic application: A highly substrate-selective Wittig reaction. We also report that this property renders the capsule an efficient enzyme-like catalyst for substrate selective diethyl acetal hydrolysis.
authors.affiliation: Department Chemie, Technische Universität München , D-85747 Garching, Germany.
authors.forename: Qi
authors.initials: Q
authors.lastname: Zhang
authors.forename: Konrad
authors.initials: K
authors.lastname: Tiefenbacher
mesh_terms: D000080:Acetals / Q000737:chemistry; D064751:Ammonium Compounds / Q000737:chemistry; D047250:Calixarenes / Q000138:chemical synthesis / Q000737:chemistry*; D002384:Catalysis; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D008958:Models, Molecular; D008968:Molecular Conformation; D010649:Phenylalanine / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry; D011522:Protons
chemical_list: D000080:Acetals; D064751:Ammonium Compounds; D011522:Protons; C466160:resorcinarene; D047250:Calixarenes; D010649:Phenylalanine