β-Selective Aroylation of Activated Alkenes by Photoredox Catalysis

Late-stage synthesis of α,β-unsaturated aryl ketones remains an unmet challenge in organic synthesis. Reported herein is a photocatalytic non-chain-radical aroyl chlorination of alkenes by a 1,3-chlorine atom shift to form β-chloroketones as masked enones that liberate the desired enones upon workup. This strategy suppresses side reactions of the enone products. The reaction tolerates a wide array of functional groups and complex molecules including derivatives of peptides, sugars, natural products, nucleosides, and marketed drugs. Notably, addition of 2,6-di-tert-butyl-4-methyl-pyridine enhances the quantum yield and efficiency of the cross-coupling reaction. Experimental and computational studies suggest a mechanism involving PCET, formation and reaction of an α-chloro-α-hydroxy benzyl radical, and 1,3-chlorine atom shift.

Acyl Radical Smiles Rearrangement To Construct Hydroxybenzophenones by Photoredox Catalysis

The first visible-light-induced acyl radical Smiles rearrangement to transform biaryl ethers to hydroxybenzophenones under mild and metal-free conditions is reported. Using the dual catalysis of hypervalent iodine(III) reagents and organophotocatalysts, ketoacids readily generate acyl radicals and undergo 1,5- ipso addition. This method can construct electron-deficient and electron-rich hydroxybenzophenones with excellent chemoselectivity and on gram scale. The performance of the reaction in neutral aqueous conditions holds potential for future biomolecule applications.

Synthesis of indolo[2,1-a]isoquinoline derivatives via visible-light-induced radical cascade cyclization reactions

We describe a photocatalyzed transformation for the synthesis of the indolo[2,1-a]isoquinoline core structure.

Access to 2,3-Fused Pyrroles via Visible Light Driven Coupling of α-Azidochalcones with 1/2-Naphthols, or 2-Hydroxy-1,4-Naphthoquinone

α-Azidochalcones were coupled with 1/2-naphthols or 2-hydroxy-1,4-naphthoquinone using Ru(bpy)₃(PF₆)₂ as a photocatalyst under blue LED light irradiation to yield 2,3-fused pyrroles in high yields (68-84%). The overall transformation involves photosensitized decomposition of α-azidochalcones into highly reactive 2 H-azirines which are trapped by 1/2-naphthols or 2-hydroxy-1,4-naphthoquinone, leading to the construction of two new C-N and one new C-C bonds.

Photoredox Catalysis for Building C-C Bonds from C(sp2)-H Bonds

Transition metal-catalyzed C-H bond functionalizations have been the focus of intensive research over the last decades for the formation of C-C bonds from unfunctionalized arenes, heteroarenes, alkenes. These direct transformations provide new approaches in synthesis with high atom- and step-economy compared to the traditional catalytic cross-coupling reactions. However, such methods still suffer from several limitations including functional group tolerance and the lack of regioselectivity. In addition, they often require harsh reaction conditions and some of them need the use of strong oxidant, in a stoichiometric amount, avoiding these processes to be truly eco-friendly. The use of photoredox catalysis has contributed to a significant expansion of the scope of C(sp²)-H bond functionalizations which include the direct arylations, (perfluoro)alkylations, acylations, and even cyanations. Most of these transformations involve the photochemical induced generation of a radical followed by its regioselective addition to arenes, heteroarenes, or alkenes, leading to the building of a new C(sp²)-C bond. The use of photoredox catalysis plays crucial roles in these reactions promoting electron transfer, enabling the generation of radical species and single electron either oxidation or reduction. Such reactions operating at room temperature allow the building of C-C bonds with high chemo-, regio-, or stereoselectivity. This review surveys the formation of C(sp²)-C bonds initiated by photoredox catalysis which involves a C(sp²)-H bond functionalization step, describes the advantages compared to traditional C(sp²)-H bond functionalizations, and presents mechanistic insights into the role played by the photoredox catalysts.

Photoredox-Induced Intramolecular 1,5-H Transfer Reaction of Aryl Iodides for the Synthesis of Spirocyclic γ-Lactams

This work develops a photocatalysis method for the synthesis of γ-spirolactams through a tandem intramolecular 1,5-HAT reaction-cyclization process. A variety of novel γ-spirolactams are prepared in good to excellent yields with this method. This transformation features mild reaction conditions and exceptional functional group tolerance. Additionally, γ-terpinene is applied to this transformation as a hydrogen atom donor for the first time.

Visible-Light-Mediated Ipso-Carboacylation of Alkynes: Synthesis of 3-Acylspiro[4,5]trienones from N-(p-Methoxyaryl)propiolamides and Acyl Chlorides

A novel visible-light-mediated ipso-carboacylation of N-(p-methoxyaryl)propiolamides with acyl chloride has been established for the synthesis of diverse 3-acylspiro[4,5]trienones with high selectivity and efficiency. This method represents a new difunctionalization of alkynes through cross coupling of the acyl chloride C-Cl bonds with an ipso-aromatic carbon by simultaneously forming two new carbon-carbon bonds and one carbon-oxygen double bond.

The radical acylarylation of N-arylacrylamides with aliphatic aldehydes using the photolysis of hypervalent iodine(iii) reagents

This article describes a variety of 3,3-disubstituted 2-oxindoles that bear carbonyl groups, which are efficiently obtained from a radical reaction between N-arylacrylamides and aliphatic aldehydes. The reaction is initiated by the photolysis of hypervalent iodine(iii) reagents and proceeds smoothly under mild, metal-free conditions.

Visible-light induced tandem radical cyanomethylation and cyclization of N-aryl acrylamides: access to cyanomethylated oxindoles

A visible-light induced cyanomethylation of N-aryl acrylamides with bromoacetonitrile followed by intramolecular cyclization has been explored.