Synthesis of Indoles Using Visible Light: Photoredox Catalysis for Palladium‐Catalyzed CH Activation

Abstract

A combined palladium- and photoredox-catalyzed C-H olefination enables the synthesis of indoles. By using visible light, the direct C-H activation of aromatic enamines can be achieved and a variety of indole derivatives can be obtained in good yields under mild reaction conditions.

Photoredox Catalysis in Organic Chemistry

“…90 Here, the photocatalyst is proposed to facilitate reoxidation of the generated Pd(0) catalyst by either direct SET or through reductive generation of superoxide. Subsequently, Rueping demonstrated that photoredox catalysis could also aid Ru- and Rh-catalyzed oxidative Heck reactions in a mechanistically analogous manner.…”

Catalysis with Palladium Complexes Photoexcited by Visible Light

“…[2] Recently,i tw as reported that excitation by visible light in the absence of exogenous photosensitizers [3][4][5] resulted in the generated photoexcited Pd complexes undergoing single-electron transfer (SET) processes to generate hybrid Pd/radical species [6] through aP d 0 / Pd I pathway (Scheme 1, excited state). [7] Thes cope and mechanistic aspects of this new reactivity are discussed, and is organized by the type of hybrid Pd/radical intermediates produced. Additionally,the photoexcited Pd complexes are also capable of dramatically accelerating known Pd-catalyzed transformations,s uch as Heck and Negishi cross-coupling reactions of aryl halides.T his Minireview summarizes the recent progress in the emerging area of photoexcited Pd catalysis without employment of exogenous photosensitizers.…”

Merging Visible‐Light Photocatalysis and Palladium Catalysis for C−H Acylation of Azo‐ and Azoxybenzenes with α‐Keto Acids

“…In contrast, when the same solution was under the blue LED irradiation, a signal of trapped radical O 2 − ⋅ was clearly observed (Figure b). It revealed that the superoxide radical anion (O 2 − ⋅) is generated from the molecular oxygen by single‐electron transfer (SET),, under the present reaction conditions.…”