Photoredox Catalyzed Radical Cascade Aroylation (Sulfonylation)/Cyclization Enables Access to Fused Indolo-pyridones

Abstract

A visible-light-initiated radical cascade reaction toward the synthesis of structurally diverse fused Indolo-pyridones is described. The reaction involves the addition of aroyl or sulfonyl radicals to N-alkyl-acryloyl-1H-indole-3-carboxamides, cyclization, and oxidative aromatization. This telescoped method circumvents lengthy prefunctionalization steps of radical precursors, which is further underpinned by the superior compatibility with a series of C-centered radicals, allowing the rapid and facile construction of numerous valuable architectures.

Radical Cascade Cyclization of Alkene‐Tethered Compounds: Versatile Approach towards Ring‐Fused Polycyclic Structures

“…In 2021, He and Guan's group described a photoredox catalyzed radical cascade aroylation(sulfonylation)/cyclization of N ‐alkyl‐acryloyl‐1 H ‐indole‐3‐carboxamides for the synthesis of aroylated and sulfonylated indolo‐pyridones (Scheme 64). [108] Aroyl and sulfonyl chlorides were used as the radical sources.…”

C−N and C−C Bond Formation in Annulation and Aromatization through Metal‐Catalyzed Photoredox C−H Functionalization

“…The corresponding compounds were produced in moderate to good yields by the radical acceptors which had indole rings protected by N‐benzyl and N−Ts [Scheme 39]. [47] …”

“…The corresponding compounds were produced in moderate to good yields by the radical acceptors which had indole rings protected by Nbenzyl and NÀ Ts [Scheme 39]. [47] Another protocol to construct Oxaindoles 170 by hydroarylation of activatyed alkene 169 via proton coupled electron transfer was reported by Liu and group in 2021. In the following neutral hydroarylation reaction feasibility occurs for the reaction of the reaction of N-methyl-N-phenyl methacrylamide 169 (0.2 mmol), irridium as a photocatalyst (2.0 mol %) with TfOH (1.0 equiv), LiBr (30 mol %), H 2 O (20 equiv), and PhCl (0.2 M) under a N 2 atmosphere and 35 W blue LEDs at room temperature (25-35 °C) for 24 h. The photocatalytic system combines with brønsted acid and bromide additive features high 5-exo-trig selectivity through proton-coupled electron transfer (PCET) and SET.…”

Metal-Free Generation of Acyl Radical via Photoinduced Single-Electron Transfer from Lewis Base to Acyl Chloride

“…Photoredox-catalyzed acyl radical chemistry has been developed to be a powerful tool for the synthesis of a wide range of heterocycles and (α,β-unsaturated) aryl ketones from carboxylic acids, anhydrides, pyruvic acids, thioesters, aldehydes, etc . In this regard, significant progress has been achieved in the photoredox-catalyzed generation of acyl radicals from acyl chlorides by the research groups of Xu, Ngai, and others (Figure C) . Generally, most of these procedures rely on strongly reducing photocatalysts.…”