Fullerene C₇₀ as Photoredox Catalyst for the Synthesis of Pyrrolo[2,1-a]isoquinolines by 1,3-Dipolar Cycloaddition-Aromatization Sequence

Herein, fullerene (C₇₀ ) is introduced as an effective photoredox catalyst for the construction of a highly functionalised pyrrolo[2,1-a]isoquinoline framework by 1,3-dipolar cycloaddition-aromatisation reaction sequence. The ability of C₇₀ to efficiently harvest visible light, its long-triplet state lifetime, good photostability, and strong singlet oxygen generation potential (Φ_▵ ≈1), make it an efficient photoredox catalyst. Upon photoirradiation, C₇₀ promotes the formation of singlet oxygen and superoxide radical by energy transfer (EnT) and single electron transfer (SET) mechanism. The superoxide radical acts as a potential oxidant in the formation of azomethine ylide through the oxidation-deprotonation tandem process. Azomethine ylide further participates in [3+2]-cycloaddition reaction protocol with alkene/alkyne to give the corresponding pyrrolo[2,1-a]isoquinolines. Interestingly, this protocol allows the activation of a wide range of substrates giving access to a diverse library of 48 well-decorated pyrrolo[2,1-a]isoquinolines with good functional group tolerance.