Pd-Catalyzed Cyclocarbonylation of 2-(2-Bromoaryl)indoles with CO as a C1 Source: Selective Access to 6H-Isoindolo[2,1-a]indol-6-ones and Indeno[1,2-b]indol-10(5H)-ones

A highly efficient and regioselective synthetic route to 6H-isoindolo[2,1-a]indol-6-ones and indeno[1,2-b]indol-10(5H)-ones through the Pd-catalyzed cyclocarbonylation of 2-(2-bromoaryl)indoles under atmospheric CO pressure has been achieved. Notably, the regioselectivity of the reaction was exclusively dependent on the structural characteristics of the indole substrates. With N-unsubstituted indoles as the starting materials, the reaction afforded 6H-isoindolo[2,1-a]indol-6-ones in good-to-excellent yields. On the other hand, with N-substituted indoles as the substrates, the reaction gave indeno[1,2-b]indol-10(5H)-ones in a highly regioselective manner.