Achiral and Chiral Higher Adducts of C70 byBingel Cyclopropanation

Regiochemically Controlled Synthesis of a β-4-β′ [70]Fullerene Bis-Adduct

“…The number of possible tetra-adduct isomers that can be obtained starting from the BA-MB-C 70 tris-adduct , is 16, and only one is C 2v -symmetric (Figure b). , …”

“…The NOESY-NMR spectrum of BA-BB-C 70 exhibited a weak correlation between the methyl (−CH 3 ) protons of the ethyl malonates and the methylene protons of the anthracene addends (Figure S8). This correlation shows that the third and fourth additions occurred at the C 2v -symmetric β-bonds close to the anthracene groups and not to the other possible α- or β-bonds, for which no correlation would be observed …”

“…34 signals for the sp 2 carbons were observed in the 13 C NMR spectrum (Figure S6), in agreement with the C s -symmetry observed in the 1 H NMR. The preferential formation of a single C s -symmetric tris-adduct starting from the α-6-α′ bis-adduct was supported by MO calculations, which showed that the calculated α-6-α′ bis-adduct has enhanced LUMO coefficients at the C s -symmetric β-bonds . Addition to any of the other α- or β-bonds will result with a sterically congested product.…”

“…Additionally, we confirmed that MB-C 70 corresponds to the β-isomer by comparison of the UV–vis absorption spectrum with those of previously reported β-pyrrolidine C 70 derivatives (Figure S13). , As far as we know, this synthetic approach becomes the only methodology to selectively synthesize the uncommon β-Bingel mono-adduct. ,, …”

“…Thus, when identical addends are used and additions exclusively to [6,6]-bonds are considered, the number of statistically possible bis-regioisomers are 8 for C 60 and 64 for C 70 . There are very few examples of tris- and tetra-adducts of C 70 : the first one was reported in 1995 by Diederich et al They started from the 5 o’clock or the 12 o’clock bis-adduct α-9-α′ or α-6-α′, respectively, using a recently introduced nomenclature and added an excess of bromo-ethylmalonate to obtain one tris-adduct and one C 2 - or C 2v -symmetric tetra-adduct isomer, respectively. , …”