One-pot Synthesis of Indolino[2′,3′:1,2][60]fullerenes from Fullerene Epoxide: Lewis Acid-assisted Nucleophilic Addition Followed by Intramolecular Cyclization

Abstract

An efficient one-pot method for the synthesis of indolino[2′,3′:1,2][60]fullerene derivatives was developed, in which the formation and cyclization of a β-amino alcohol intermediate by the nucleophilic reaction of fullerene epoxide with aromatic amines was promoted in the presence of aprotic heterogeneous catalysts.

Notably Enhanced Reactivity of the Fulleroid anti‐Bredt Double Bond in Diels–Alder Reactions

“…[12b,12d] Accordingly, the diagnostic methine protons of 1b (3.8 ppm), 1c (3.7 ppm) and 1d (4.1 ppm) are comparably in agreement with the location above the hexagon ring of [5,6]-opened fulleroid. The lower field resonances of 1b and 1c compared with that of 1a (2.9 ppm) may be due to the presence of the geminal, electron-withdrawing R 2 substituents.…”

“…Fullerenes can easily undergo various types of reactions such as nucleophilic addition and cycloaddition exclusively at the [6,6]-conjugated double bond. [1] The major driving force for such addition reactions is the resulting relief of strain due to the higher pyramidalization [2] of angles of the sp2 C atoms in the fullerene spherical surface as well as the highly π-conjugated lowest unoccupied molecular orbital (LUMO).…”

“…For example, fullerene epoxide, [4] with a highly reactive three-membered ring, has been used as a reactive candidate to obtain structurally-defined biaryl- [5] and cycloaminofullerenes. [6] However, the initial epoxidation of fullerene by photooxy-…”

“…Based on product analysis, the enhanced reactivity was ascribed to the exclusive addition at the highly strained bridgehead double bond of the transannular [5,6] open ring orifice. It was concluded that the twisted anti-Bredt double bond can perform a topologically suitable [ π 2 s + π 4 s ] orbital interaction with the less congested, labile dienes.…”

“…[9] An alternative way of endowing the fullerene cages with enhanced reactive sites is the introduction of a transannular [5,6]opened bond as in fulleroids and azafulleroids. Azafulleroids have been widely used as reagents for the ring-enlargement of a fullerene orifice by the regioselective [2 + 2] addition of singlet oxygen to the bridgehead olefin.…”