Preparation and Characterization of Six Bis(N-methylpyrrolidine)−C60 Isomers: Magnetic Deshielding in Isomeric Bisadducts of C60

Abstract
A series of isomers of bis(N-methylpyrrolidine)-C(60) 2 (Prato bisadducts) was prepared by the 1,3-dipolar cycloaddition of N-methylazomethine ylide to C(60). Six isomers were separated and characterized by ESI-MS, UV/vis, and (1)H and (13)C NMR spectroscopy. The structures of these bisadducts were assigned based on (1) comparison of their molecular symmetries with their (1)H and (13)C NMR spectra, (2) comparison of their UV/vis spectra with those of corresponding Bingel-Hirsch bisadducts, and (3) the order of deshielding of the methylene and N-methyl (1)H NMR resonances. Prato bisaddition is less chemoselective than Bingel-Hirsch bisaddition to C(60).