Preparation and identification of bis(formylmethano)[60]fullerene isomers: The first systematic study on bifunctionalized [60]fullerenes with dissymmetric addends

Fourteen isomers of bis(formylmethano)C60 were isolated and characterized. A mixture of the bisadducts was obtained by the reaction of C60 with an -formylsulfonium ylide, and then separated into fifteen fractions by preparative HPLC, preparative TLC, and recycling preparative HPLC. Fourteen of fifteen fractions were found to consist of a single isomer, respectively, which were assigned to the trans-2 (3 diastereo-isomers), trans-3 (3 diastereo-isomers), trans-4 (3 diastereo-isomers), equarorial (2 diastereo-isomers), and cis-2 (3 diastereo-isomers) bisadducts by the comparison of their UV/vis spectra with those of the bisadducts obtained by the Bingel-Hirsch reaction. The 1H- and 13C-NMR analysis, the transformation of the formyl groups, and the dipole moment calculation clarified the stereochemistry of the subsitutents on the two cyclopropane bridge-head carbons (in/in, in/out, and out/out)