Diastereoselective syntheses and oxygenation of silyl fulleroids

The addition of silyl diazomethane (1a–d) to fullerene C60 at room temperature provided the mono-adducts, the bis- and tris-adducts of silyl fulleroid (3a–d) in moderate yields. The structures of the silyl fulleroids were characterized by mass spectroscopy, as well as 1H and 13C NMR. The gated 1H NMR and 13C–1H COLOC analyses of 3a–d showed a correlation between the methine proton resonances and three fullerene carbons. These observations, as well as the 1H NMR chemical shifts of the methine protons, suggest a remarkable diastereoselectivity, with the silyl groups located above a five-membered ring. Two transition states of the thermal nitrogen-extrusion of pyrazoline intermediate (2a) were theoretically obtained, the structures of which disclosed that the diastereoselectivity is a consequence of minimization of the repulsive interaction between the silyl groups and the N2 moiety. The bridgehead Cdouble bond; length as m-dashC double bond of the silyl fulleroid is thought to be reactive by POAV analyses. The silyl fulleroids (3a,b) were found to react with singlet oxygen to afford the silyl enol ether (9a,b) via 1,3-silyl migration of a diketone (8a,b). This is the first example of 1O2 oxygenation of fulleroids.