On the Barton Copper-Catalyzed C3-Arylation of Indoles using Triarylbismuth bis(trifluoroacetate) Reagents

We disclose herein our detailed investigation into the Barton copper-promoted C3-arylation of indoles using triarylbismuth bis(trifluoroacetates). The arylation of unsubstituted 1H-indole using Barton's conditions gave a low yield of the C3-arylated indole, along with small amounts of the product of double C2/C3-arylation and traces of the product of C2 arylation. On the contrary, the arylation of indoles blocked at the C2 position is highly efficient, affording the desired products of C3-arylation in good to excellent yields. The reaction operates under simple conditions, shows good substrate scope, excellent functional group compatibility, and allows the transfer of electron-neutral or deficient aryl groups. Computational studies propose a mechanism involving a trifluoroacetate-assisted C-H activation step.

Automated summary

In this study, we investigated the Barton copper-promoted C3-arylation of indoles using triarylbismuth bis(trifluoroacetates) in detail. Under Barton's conditions, the arylation of unsubstituted 1H-indole gave low yield of C3-arylated indole, along with small amounts of double C2/C3-arylation product and traces of C2 arylation product. On the contrary, the arylation of indoles blocked at the C2 position was highly efficient and provided desired products of C3-arylation in good to excellent yields. The reaction showed simple conditions, good substrate scope, excellent functional group compatibility, and allowed the transfer of electron-neutral or deficient aryl groups. Computational studies proposed a mechanism involving a trifluoroacetate-assisted C-H activation step.