Electrochemical and H/D-labeling study of oxazolino[60]fullerene rearrangement.

Isomerization of an oxazoline cycle from a [6,6]- to [5,6]-junction on the C(60) sphere of dianionic [60]fullero-oxazoline (1(2-)) during a 1,4-addition is studied by electrochemistry and a stepwise addition of PhCH(2)Br and PhCD(2)Br. Cyclic voltammerty of the in situ generated 1(2-) shows a very unusual positive shift for the anodic peak corresponding to the oxidation of 1(2-), indicating that the C(60) cage of dianionic 1 bears only one unit negative charge due to the heterolytic cleavage of the C(60)-O bond. Further study with a stepwise addition of PhCH(2)Br and PhCD(2)Br, which are used to differentiate the aryl groups added at each step onto dianionic 1, shows explicitly there is an exclusive selectivity of the C-O bond for the ring-opening and ring-closure during the isomerization of the heterocycle. A reaction mechanism is proposed on the basis of the experimental results and computational calculations.