Approaches to Open Fullerenes:  Synthesis and Kinetic Stability of Diels−Alder Adducts of Substituted Isobenzofurans and C₆₀

Abstract

We have examined the reactions of 1,3-disubstituted isobenzofurans with the fullerene C60 in the context of an approach to open a large orifice on the fullerene framework. A variety of substituted isobenzofurans (6a-h), generated from the reaction of 1,4-substituted 1,4-epoxynaphthalenes 3a-h with 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine (4a) or 1,2,4,5-tetrazine (4b), were added to C60 to afford the Diels-Alder adducts 7a-h. The thermal stability of these adducts toward retro-Diels-Alder fragmentation differs greatly in solution from that in the solid state. In solution, the relatively facile retro-Diels-Alder fragmentation of monoadducts 7a and 7c, to give C60 and the free isobenzofurans 6a and 6c, have rate constants (and activation barriers) of k=9.29x10(-5) s-1 at 70 degrees C (Ea=32.6 kcal mol-1) and k=1.36x10(-4) s-1 at 40 degrees C (Ea=33.7 kcal mol-1), respectively, indicating that the addition of isobenzofurans to C60 is readily reversible at those temperatures. In the solid state, thermogravimetric analysis of adduct 7a indicates that its decomposition occurs only within the temperature range of 220-300 degrees C. As a result, these compounds can be stored at room temperature in the solid state for several weeks without significant decomposition but have to be handled within several hours in solution.

Biobased C6-Furans in Organic Synthesis and Industry: Cycloaddition Chemistry as a Key Approach to Aromatic Building Blocks

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Diels−Alder Chemistry of Graphite and Graphene: Graphene as Diene and Dienophile

“…A further increase in temperature led to products with a decreased amount of functionality because of the thermal instability of the DA adducts; the cycloreversion process was complete at 150 °C. Diels−Alder adducts of fullerenes were found to be stable up to temperatures of ∼40 °C in solution but were much more thermally stable in the solid state …”

Regio- and stereospecific synthesis of a new benzoconduritol-C derivative

“…Oxabenzonorbornadiene 5 was prepared using benzenediazonium-2-carboxylate hydrochloride and furan. 37,38 This compound was used to synthesise 3-(2-bromo-phenoxy)-1,2,3,4-tetrahydronaphthalene-1,2,4-triol 10. This synthesis was inspired from the key compound.…”