title: Approaches to open fullerenes: synthesis and thermal stability of cis-1 bis(isobenzofuran) Diels-Alder adducts of C60.
abstract: In a quest to form wider openings within the cage of the fullerene C60 through controlled bond-breaking reactions, we have examined the double saturation of adjacent C=C bonds within a six-membered ring of C60. We have investigated the double Diels-Alder cycloaddition of two tethered isobenzofurans to the fullerene C60. We obtained cis-1 adducts in good yields after reacting the methylene- or quinoxaline-tethered bis(isobenzofuran) precursors 2a-k with parent 3,6-dihydro-1,2,4,5-tetrazine (3b). The X-ray structure of the methylene-tethered bis(isobenzofuran)-C60 adduct 4b has been obtained; four-eclipsed substituents are held rigidly by the bicyclic addends. The cis-1 bis(isobenzofuran) bisadducts 4b and 4e-j are kinetically far more stable toward thermal retro-Diels-Alder fragmentation than are mono(isobenzofuran) adducts of C60, in solution and in the solid state as determined by 1H NMR spectroscopy or thermogravimetric analysis. A methodology for the reversible solubilization of other fullerene derivatives based on this work is also presented.
authors: Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, USA.
authors: Michael
authors: M
authors: Sander
authors: Thibaut
authors: T
authors: Jarrosson
authors: Shih-Ching
authors: SC
authors: Chuang
authors: Saeed I
authors: SI
authors: Khan
authors: Yves
authors: Y
authors: Rubin
mesh_terms: D001572:Benzofurans / Q000138:chemical synthesis* / Q000737:chemistry; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D003500:Cyclization; D037741:Fullerenes / Q000737:chemistry*; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure; D013237:Stereoisomerism; D013696:Temperature
chemical_list: D001572:Benzofurans; D037741:Fullerenes; C069837:fullerene C60