title: Comprehensive Synthesis of Monohydroxy-Cucurbit[n]urils (n = 5, 6, 7, 8): High Purity and High Conversions.
abstract: We describe a photochemical method to introduce a single alcohol function directly on cucurbit[n]urils (n = 5, 6, 7, 8) with conversions of the order 95-100% using hydrogen peroxide and UV light. The reaction was easily scaled up to 1 g for CB[6] and CB[7]. Spin trapping of cucurbituril radicals combined with MS experiments allowed us to get insights about the reaction mechanism and characterize CB[5], CB[6], CB[7], and CB[8] monofunctional compounds. Experiments involving (18)O isotopically labeled water indicated that the mechanism was complex and showed signs of both radical and ionic intermediates. DFT calculations allowed estimating the Bond Dissociation Energies (BDEs) of each hydrogen atom type in the CB series, providing an explanation of the higher reactivity of the "equatorial" C-H position of CB[n] compounds. These results also showed that, for CB[8], direct functionalization on the cucurbituril skeleton is more difficult because one of the methylene hydrogen atoms (Hb) has its BDE lowering within the series and coming close to that of Hc, thus opening the way to other types of free radicals generated on the CB[8] skeleton leading to several side products. Yet CB[5]-(OH)1 and CB[8]-(OH)1, the first CB[8] derivative, were obtained in excellent yields thanks to the soft method presented here.
authors.affiliation: †Aix-Marseille Université, CNRS, Institut de Chimie Radicalaire, UMR 7273, 13397 Marseille, France.|‡Department of Chemistry, Gebze Technical University, P.K.:141, 41400 Gebze, Kocaeli, Turkey.
authors.forename: Mehmet M
authors.initials: MM
authors.lastname: Ayhan
authors.affiliation: †Aix-Marseille Université, CNRS, Institut de Chimie Radicalaire, UMR 7273, 13397 Marseille, France.
authors.forename: Hakim
authors.initials: H
authors.lastname: Karoui
authors.affiliation: †Aix-Marseille Université, CNRS, Institut de Chimie Radicalaire, UMR 7273, 13397 Marseille, France.
authors.forename: Micaël
authors.initials: M
authors.lastname: Hardy
authors.affiliation: § Institute of Materials and Environmental Chemistry, Hungarian Academy of Sciences, Department of Physics, Budapest University of Technology and Economics, Budafoki ut 8, 1111 Budapest, Hungary.
authors.forename: Antal
authors.initials: A
authors.lastname: Rockenbauer
authors.affiliation: †Aix-Marseille Université, CNRS, Institut de Chimie Radicalaire, UMR 7273, 13397 Marseille, France.
authors.forename: Laurence
authors.initials: L
authors.lastname: Charles
authors.affiliation: ∥Aix-Marseille Université, CNRS, Spectropole, FR 1739, 13013 Marseille, France.
authors.forename: Roselyne
authors.initials: R
authors.lastname: Rosas
authors.affiliation: ⊥National Research Council Canada, 100 Sussex Drive, Ottawa, ON K1A 0R6, Canada.
authors.forename: Konstantin
authors.initials: K
authors.lastname: Udachin
authors.affiliation: †Aix-Marseille Université, CNRS, Institut de Chimie Radicalaire, UMR 7273, 13397 Marseille, France.
authors.forename: Paul
authors.initials: P
authors.lastname: Tordo
authors.affiliation: †Aix-Marseille Université, CNRS, Institut de Chimie Radicalaire, UMR 7273, 13397 Marseille, France.
authors.forename: David
authors.initials: D
authors.lastname: Bardelang
authors.affiliation: †Aix-Marseille Université, CNRS, Institut de Chimie Radicalaire, UMR 7273, 13397 Marseille, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Ouari