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

Electrochemical synthesis of γ-carbolinones via sulfonylation-triggered cyclization of indole-3-carboxamides

A novel electrochemical radical cyclization reaction of N-acryloyl-indole-3-carboxamides with sodium sulfinates as coupling partners has been developed, which delivers multi-substituted γ-carbolinones as products with up to 70% yields. This study represents the first example of the radical cyclization reaction of indole-3-carboxamides under electrochemical conditions. The reaction features a broad substrate scope of sodium sulfinates and indole-3-carboxamides, and provides a new and efficient strategy for the synthesis of γ-carbolinone derivatives.

Visible-light-induced radical cascade sulfonylation/cyclization towards indole-fused pyridine derivatives

Indole-fused pyridines are an important motif in pharmaceuticals and functional molecules. A visible-light induced Ru(bpy)3Cl2·6H2O catalyzed radical cascade sulfonylation/cyclization strategy for the synthesis of indole-fused pyridine derivatives was developed. Diverse indole-fused pyridines bearing different functional groups were obtained in moderate to good yields. Compared with previous work, the easily accessible starting materials, molecular nitrogen as byproduct, and eco-friendly visible light as an energy source all make this transformation more sustainable and practical.

Visible light-induced cascade sulfonylation/annulation of ortho-allyloxy chalcones with sodium sulfinates for the synthesis of sulfonated chromane derivatives

A visible-light-induced radical cascade reaction for the synthesis of structurally diverse sulfonated chromanes is described. The protocol involves the addition of sulfonyl radicals to ortho-allyloxy chalcones and intramolecular Michael addition reactions in the presence of eosin Y as a photocatalyst. Additionally, this protocol shows that it is also an effective method to construct seven-membered oxygen-containing heterocycles. The method features a wide substrate scope, the use of easily accessible materials and excellent functional group tolerance with high to excellent yields. Control experiments and mechanistic studies indicate that a visible light-induced radical cascade process is involved in the transformation.

Photocatalytic Sulfonylation: Innovations and Applications

Photosynthesis, converting sustainable solar energy into chemical energy, has emerged as a promising craft to achieve diverse organic transformations due to its mild reaction conditions, sustainability, and high efficiency. The synthesis of sulfonated compounds has drawn significant attention in the pharmaceuticals, agrochemicals, and materials industries due to the unique structure and electronic properties of the sulfonyl groups. Over the past decades, many photocatalytic sulfonylation reactions have been developed. In this review, the recent advances in photocatalyzed sulfonylation have been reviewed since 2020, with a primary focus on discussing reaction design and mechanism.

Oxidant-Assisted Sulfonylation/Cyclization Cascade Synthesis of Alkylsulfonylated Oxindoles via the Insertion of SO2

An oxidant-assisted tandem sulfonylation/cyclization of electron-deficient alkenes with 4-alkyl-substituted Hantzsch esters and Na2S2O5 for the preparation of 3-alkylsulfonylated oxindoles under mild conditions in the absence of a photocatalyst and transition metal catalyst is established. The mechanism studies show that the alkyl radicals, which come from the cleavage of the C-C bond in 4-substituted Hantzsch esters under oxidant conditions, subsequently undergo the in situ insertion of sulfur dioxide to generate the crucial alkylsulfonyl radical intermediates. This three-component reaction provides an efficient and facile route for the construction of alkylsulfonylated oxindoles and avoids the use of highly toxic alkylsulfonyl chlorides or alkylsulfonyl hydrazines as alkylsulfonyl sources.

Photoinduced N-Heterocyclic Nitrenium-Catalyzed Single Electron Reduction of Acyl Fluorides for Phenanthridine Synthesis

Acyl fluorides are versatile reagents in organic synthesis. However, there is no precedent to employ acyl fluorides as acyl radical precursors. We herein report an N-heterocyclic nitrenium iodide salt-catalyzed photoreduction of acyl fluorides to produce acyl radicals, which could react with 2-isocyanobiaryls to afford various carbonyl phenanthridines.