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Nickel-Promoted First Ene−Diyne Cycloaddition Reaction on C60:  Synthesis and Photochemistry of the Fullerene Derivatives

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journal contribution
posted on 13.11.1998, 00:00 by Tsung-Yu Hsiao, K. C. Santhosh, Kou-Fu Liou, Chien-Hong Cheng
A novel method for the construction of a fused cyclohexadiene ring on C60 based on a nickel-promoted [2+2+2] cycloaddition of 1,6-diynes is described. Treatment of C60 with terminal 1,6-diynes (HC⋮CCH2)2X) in the presence of NiCl2(PPh3)2, Zn, and PPh3 at 90 °C in toluene afforded [2+2+2] bicyclic hexadiene derivatives (X = C(CO2Me)2 (2a), C(CO2Et)2 (2b), C(COMe)2 (2c), CH2 (2d), O (2e), NSO2-p-C6H5CH3 (2f), C(SO2Ph)2 (2g), and (2h) in good yields. Spectral data for products 2ah indicated that the cycloaddition of diynes to C60 occurs across a 6,6-ring junction on the fullerene. On the basis of the established chemistry of metal-mediated [2+2+2] cycloaddition, a mechanism is proposed to account for the present nickel-mediated reaction. All the hexadiene derivatives 2ah in solution are readily oxidized by molecular oxygen in the presence of light at ambient temperature. The oxidation process of compound 2a in chloroform-d was monitored by 1H NMR spectroscopy, and the results showed that 2a first reacted with molecular oxygen to form peroxide 3 and was subsequently converted to dialdehyde 4 and C60-containing polymeric material. Photochemical properties of some cyclohexadiene derivatives were then investigated. Upon irradiation (350 nm), compounds 2ac, 2f, and 2h readily underwent [4+4] cycloaddition to give the corresponding bisfulleroids 5ac, 5f, and 5h in excellent yields.

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