Heterogeneous Photocatalytic C–H Functionalization of Indoles with Diazo Compounds Enabled by Carbon Nitride

Abstract

Herein, we reported the heterogeneous photocatalytic C–H alkylation of indoles with diazo compounds using graphitic carbon nitride (g-C3N4) as the photocatalyst. The reaction was carried out under a simple operation and mild conditions. In addition, the catalyst was found to be stable and reusable after five reaction cycles. The photochemical reaction proceeds via an intermediary of a carbon radical, which is generated from diazo compounds through a visible-light-promoted proton-coupled electron transfer (PCET) process.

Visible Light-Induced Reactions of Diazo Compounds and Their Precursors

“…A year later, Hajra and co-workers reported a similar radical approach using diazo compounds for C3-alkylation of imidazopyridines under the same reaction conditions (Scheme b) . In addition to aforementioned Ru complex, graphitic carbon nitride (g-C 3 N 4 ) also could serve as a photocatalyst in alkylation of indoles with diazo compounds, as shown by Zhou and Guo …”

Catalytic C(sp2)−H Trifluoroethylation of Indoles via Iron‐Carbene Insertion

“…[25][26][27] However, on the other hand, CÀ H bond activation could be an attractive way to incorporate fluoroalkyl groups into drug candidates. Nevertheless, despite the great progress made in transition metal-catalyzed CÀ H activation (Figure 1a), [28][29][30][31][32][33][34][35] there are still a few notable techniques available for this specific kind of transformation. Although CF 3 CHN 2 has been exploited well as a versatile organic reagent and building block in the field of synthetic organic chemistry, there is still no specific protocol for the CÀ H functionalization of electron-rich arenes via trifluoroethylation.…”