Indole Functionalization via Photoredox Gold Catalysis.

The use of photoredox catalyst [Au2(dppm)2]Cl2 to initiate free-radical cyclizations onto indoles is reported. Excitation of the dimeric Au(I) photocatalyst for the reduction of unactivated bromoalkanes and bromoarenes is used for the generation of carbon-centered radicals. Previous to this work, reduction processes leading to indole functionalization utilizing photoredox catalysts were limited to activated benzylic or α-carbonyl-positioned bromoalkanes. This method offers a mild and safe alternative to organostannanes and pyrophoric initiators for access to high energy radicals that were previously inaccessible through catalytic or stoichiometric means.