Photoredox-Catalyzed Carbon Radical Generation from -Keto-N,O-acetals: Synthesis of Functionalized Azepino[1,2-a]indoles and Azepino[1,2-a]furo[3,2-b]indoles

C10a-Acetoxylated perhydroazepino[1,2-a]-indoles, accessible via visible light-mediated sensitized photooxygenation of cyclo-hepta[b]indoles, are precursors to structurally elaborate carbon-centered radicals. Their photoredox-catalyzed SET reduction by phenothiazine or phenoxazine photocatalysts, followed by fragmentation and C-O bond cleavage, liberates tricyclic alpha-amino-alpha-carbonyl radicals that readily engage in radical addition reactions with silyl enol ethers and silyl ketene acetals. The C-C functionalized azepinoindole[1,2-a]indoles are useful building blocks for the synthesis of polycyclic indole derivatives as shown by the controlled borohydride reduction of a C10a-methylenecarboxylate derivative, which leads stereoselectively to tetracyclic azepino[1,2-a]furo[3,2-b]indoles. The photocatalytic method developed herein is also suitable for the radical functionalization of simple alpha-acetoxy acetophenones.