Metal-Free Synthesis of <i>N</i>-Alkyl-2,5-Unsubstituted/Monosubstituted Fulleropyrrolidines: Reaction of [60]Fullerene with Paraformaldehyde and Amines

A series of scarce N-alkyl-2,5-unsubstituted/monosubstituted fulleropyrrolidines were synthesized in moderate to excellent yields by the simple one-step thermal reaction of [60]fullerene with primary/secondary amines in the presence of paraformaldehyde without the addition of valuable metal salts. Intriguingly, the reaction with primary amines unexpectedly afforded N-alkyl-2,5-unsubstituted fulleropyrrolidines instead of the anticipated 2,5-monosubstituted fulleropyrrolidines. A plausible reaction pathway is proposed to elucidate the above-mentioned reaction process based on the experimental results.