Photocatalytic Synthesis of N-Fused Pyrroles

Photocatalytic Synthesis of N-Fused Pyrroles


Carbon nitrides can be used as heterogeneous photocatalysts to promote organic reactions. Potassium poly(heptazine imide) (K-PHI), for example, is a member of the carbon nitride family and can efficiently catalyze different oxidation processes. One such reaction is the addition of aminium radicals (R2N) to double bonds. Examples of this type of reaction with C=O bonds, however, are rare.

Aleksandr Savateev, Max-Planck Institute of Colloids and Interfaces, Potsdam, Germany, and colleagues have developed a photocatalytic reaction between tetrahydroisoquinoline and chalcones (a type of aromatic ketone) that gives N-fused pyrroles (pictured). The reaction uses K-PHI as a heterogeneous, recyclable photocatalyst that is active under visible light. Using tetrahydroisoquinoline (THIQ) derivatives as a source of aminium radicals, the team converted a range of chalcones to the corresponding N-fused pyrroles, i.e., 1,3-disubstituted-5,6-dihydropyrrolo[2,1-a]isoquinolines (DHPIQ), in the presence of K-PHI under a blue LED.

The reaction proceeds in good to excellent yields. According to the researchers, the C–N bond between THIQ and the carbon atom of the C=O group is formed by the coupling of a THIQ-derived radical and a chalcone-derived radical. The pyrrole ring is then formed via a Mannich-like cyclization. The products show strong fluorescence in the blue region with an internal quantum efficiency (IQE) of up to 24 %.


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