Anefficient approach to chiral fullerene derivatives by catalytic enantioselective 1,3-dipolar cycloadditions

Fullerene chirality is an important but undeveloped issue of paramount interest in fields such as materials science and medicinal chemistry. So far, enantiopure fullerene derivatives have been made from chiral starting materials or obtained by separating racemic mixtures. Here, we report the enantioselective catalytic synthesis of chiral pyrrolidinofullerenes (the most widely studied fullerene derivatives), which proceeds in high yields under very mild conditions at low temperatures. The combination of a particular metal catalyst-Ag(I) or Cu(II)-and a chiral ligand is able to direct the cycloaddition of buckminsterfullerene C(60), the first non-coordinating dipolarophile used in such reactions, to opposite enantiofaces of N-metallated azomethine ylides. This methodology has proven to be quite general, affording enantiomeric excesses of greater than 90%. Furthermore, well-defined chiral carbon atoms linked to the fullerene sphere are able to perturb the inherent symmetry of the fullerene π-system as revealed by circular dichroism measurements.