Photoredox‐Catalyzed Carbon Radical Generation from α‐Keto‐N,O‐acetals: Synthesis of Functionalized Azepinoindoles and Azepinofuroindoles

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, fo...

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Bibliographic Details
Published in:Advanced synthesis & catalysis 2024-01, Vol.366 (1), p.24-30
Main Authors: Seefeldt, Paul, Villinger, Alexander, Brasholz, Malte
Format: Article
Language:English
Subjects:
Acetals
Carbon
Carbonyls
Ethers
Indoles
Photocatalysis
Reduction
Synthesis
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Summary: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.
ISSN:1615-4150
1615-4169
DOI:10.1002/adsc.202300967