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The C10a‐acetoxylated tetrahydroazepino[1,2‐a]indole‐6,11‐diones are a class of tricyclic oxindoles that feature an α‐keto‐N,O‐acetal substructure, rendering them highly susceptible to SET reduction followed by fragmentation. In protic medium, they undergo a PCET‐assisted two‐step reduction including an interposed C−O bond cleavage that can be initiated photocatalytically as well as by cathodic reduction, and which generates nucleophilic ketyl radicals. In the presence of acrylonitrile and DIPEA as additional reactants, the photoinduced reaction unfolds as a tandem C−O bond reduction/ketyl radical conjugate addition, to furnish C10a‐reduced, C11‐cyanoethyl‐substituted tricyclic azepino‐[1,2‐a]indole derivatives with high stereoselectivity. [ABSTRACT FROM AUTHOR]

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 α‐amino‐α‐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 α‐acetoxy acetophenones. [ABSTRACT FROM AUTHOR]