title: Methylene-bridged glycoluril dimers: synthetic methods.
abstract: Methylene-bridged glycoluril dimers are the fundamental building blocks of cucurbituril (CB[6]), its homologues (CB[n]), and its derivatives. This paper describes three complementary methods for the synthesis of C- and S-shaped methylene-bridged glycoluril dimers (29-34 and 37-44). For this purpose, we prepared glycoluril derivatives (1a-d) bearing diverse functionalities on their convex face. These glycoluril derivatives were alkylated under basic conditions (DMSO, t-BuOK) with 1,2-bis(halomethyl)aromatics 6-15 to yield 4a-d and 16-24, which contain a single aromatic o-xylylene ring and potentially nucleophilic ureidyl NH groups. Glycoluril derivatives bearing potentially electrophilic cyclic ether groups (5a-f) and 25-28 were prepared by various methods including condensation reactions in refluxing TFA containing paraformaldehyde. The condensation reactions of 4a-d and 16-24 with paraformaldehyde under anhydrous acidic conditions (PTSA, ClCH(2)CH(2)Cl, reflux) give, in most cases, the C-shaped and S-shaped methylene-bridged glycoluril in good to excellent yields. In many cases, the C-shaped compound is formed preferentially with high diastereoselectivity. Cyclic ethers 5a,d-f and 25-26 undergo highly diastereoselective dimerization reactions to yield methylene-bridged glycoluril dimers with the formal extrusion of formaldehyde. Last, it is possible to perform selective heterodimerization reactions using both cyclic ethers and glycoluril derivatives bearing ureidyl NH groups. These reactions deliver the desired C- and S-shaped heterodimers with low to moderate diastereoselectivities. This heterodimerization route is the method of choice in cases where the homodimerization reactions fail. The formation of side products (+/-)-35b and (+/-)-35d helps clarify the electronic requirements for a successful CB[n] synthesis. The X-ray structures of 30C, 38C, and 38S allow for a discussion of the structural features of this class of compounds.
authors.affiliation: Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: Anxin
authors.initials: A
authors.lastname: Wu
authors.forename: Arindam
authors.initials: A
authors.lastname: Chakraborty
authors.forename: Dariusz
authors.initials: D
authors.lastname: Witt
authors.forename: Jason
authors.initials: J
authors.lastname: Lagona
authors.forename: Fehmi
authors.initials: F
authors.lastname: Damkaci
authors.forename: Marie A
authors.initials: MA
authors.lastname: Ofori
authors.forename: Jessica K
authors.initials: JK
authors.lastname: Chiles
authors.forename: James C
authors.initials: JC
authors.lastname: Fettinger
authors.forename: Lyle
authors.initials: L
authors.lastname: Isaacs
mesh_terms: D000480:Alkynes; D018360:Crystallography, X-Ray / Q000379:methods; D019281:Dimerization; D006576:Heterocyclic Compounds, 4 or More Rings / Q000138:chemical synthesis* / Q000737:chemistry; D006838:Hydrocarbons; D007093:Imidazoles / Q000138:chemical synthesis* / Q000737:chemistry*; D008697:Methane / Q000031:analogs & derivatives*; D008958:Models, Molecular; D008968:Molecular Conformation; D006574:Heterocyclic Compounds, 2-Ring; D048289:Imidazolidines
chemical_list: D000480:Alkynes; D006576:Heterocyclic Compounds, 4 or More Rings; D006838:Hydrocarbons; D007093:Imidazoles; D008697:Methane; C030011:carbene; C092018:glycoluril; D006574:Heterocyclic Compounds, 2-Ring; D048289:Imidazolidines