N-Heterocyclic Carbene-Catalyzed α,β-Unsaturated Aldehydes Umpolung in Fullerene Chemistry: Construction of [60]Fullerene-Fused Cyclopentan-1-ones and Cyclohex-2-en-1-ones.

The first umpolung strategy for the cycloacylation of fullerene using a N-heterocyclic carbene organocatalyst is reported. The coupling of [60]fullerene with different structural α,β-unsaturated aldehydes efficiently furnishes interesting [60]fullerene-fused cyclopentan-1-ones or cyclohex-2-en-1-ones in good to excellent yields. This new reaction displays a wide substrate scope and excellent functional-group tolerance, and diverse substituents such as aryl, heteroaryl, alkenyl, alkyl, and ester can be installed by using the corresponding enals.