Visible-Light-Induced Decarboxylative Cyclization of 2-Alkenylarylisocyanides with α-Oxocarboxylic Acids: Access to 2-Acylindoles

Cu(II)-Catalyzed Decarboxylative (4 + 2) Annulation of Coumarin-3-Carboxylic Acids with In Situ Generated α,β-Unsaturated Carbonyl Compounds from tert-Propargylic Alcohols

Cu(II)-catalyzed decarboxylative oxidative (4 + 2) annulation of coumarin-3-carboxylic acids with tert-propargylic alcohols, via the in situ generated α,β-unsaturated carbonyl compounds by the Meyer-Schuster rearrangement, has been developed. This protocol involving indirect C-H functionalization offers access to diverse naphthochromenone architectures with good to excellent yields.

An MCM-41-immobilized dichloro(pyridine-2-carboxylato)gold(III) complex: an efficient and recyclable catalyst for the annulation of anthranils and ynamides

A new mesoporous MCM-41-immobilized dichloro(pyridine-2-carboxylato)gold(III) complex [MCM-41-PicAuCl₂] was synthesized via an addition reaction of a dichloro(3-hydroxypyridine-2-carboxylato)gold(III) complex to triethoxy(3-isocyanatopropyl)silane, followed by immobilization on MCM-41 and was characterized by different physico-chemical techniques. In the presence of 5 mol% of MCM-41-PicAuCl₂, the annulation reaction between anthranils and ynamides proceeded smoothly under mild conditions to afford diverse 6- or 5-formylindoles with high atom economy and good to excellent yields. This new heterogenized gold(III) complex can be easily recovered through a simple filtration process and recycled more than seven times without any apparent loss of its catalytic efficiency.

Mn(III)-Mediated Radical Addition/Cyclization of Isocyanides with Aryl Boronic Acids/Diarylphosphine Oxides: Access to 11-Functionalized Dibenzodiazepines

A Mn(III)-mediated radical addition/cyclization reaction of isocyanides with aryl boronic acids/diarylphosphine oxides has been developed. A series of 11-arylated/-phosphorylated dibenzodiazepines were efficiently constructed in moderate to excellent yields under mild reaction conditions via imidoyl radical process. The present protocol offers novel access to functionalized seven-membered N-heterocycles.

Visible-light-promoted decarboxylative radical cascade cyclization to acylated benzimidazo/indolo[2,1-a]isoquinolin-6(5H)-ones in water

A metal-free visible-light-induced decarboxylative radical addition/cyclization procedure at room temperature was described for the synthesis of acylated benzimidazo/indolo[2,1-a]isoquinolines. The procedure was prepared in water via a reaction of functionalized 2-arylbenzoimidazoles or 2,3-diarylindoles and α-oxocarboxylic acids in the presence of phenyliodine(iii) diacetate (PIDA) in one step under mild reaction conditions. In this procedure, traditional heating and metal reagents could be effectively avoided to access 1,4-dicarbonyl-containing benzimidazo/indolo[2,1-a]isoquinoline-6(5H)-ones in satisfactory yields.

Photoactive Metal Carbonyl Complexes Bearing N-Heterocyclic Carbene Ligands: Synthesis, Characterization, and Viability as Photoredox Catalysts

This report details the synthesis and characterization of a small family of previously unreported, structurally related chromium, molybdenum, tungsten, manganese, and iron complexes bearing N-heterocyclic carbene and carbonyl supporting ligands. These complexes have the general form [ML(CO)₃X] or [ML(CO)₃], where X = CO or Br and L = 1-phenyl-3-(2-pyridyl)imidazolin-2-ylidene. Where possible, the solid-state, spectroscopic, electrochemical, and photophysical properties of these molecules were studied using a combination of experiment and theory. Photophysical studies reveal that decarbonylation occurs when these complexes are exposed to ultraviolet light, with the CO ligand being replaced with a labile acetonitrile solvent molecule. To obtain insights into the potential utility, scope, and applications of these complexes in visible-light-mediated photoredox catalysis, their capacity to facilitate a range of photoinduced reactions via the reductive or oxidative functionalization of organic molecules was investigated. These chromium, molybdenum, and manganese catalysts efficiently facilitated atom-transfer radical addition processes. In light of their photolability, these types of catalysts may potentially allow for the development of photoinduced reactions involving less conventional inner-sphere electron-transfer pathways.

2,3-Difunctionalized Indoles via Radical Acylation or Trifluoromethylation of ortho-Alkynylphenyl Isonitriles

A radical cascade to 2,3-disubstituted indoles proceeding via acylation or trifluoromethylation of ortho-alkynylphenyl isonitriles is presented. In these cascades, two C-C bonds and one C-O bond are formed using an inexpensive oxidant and a catalytic copper or iron salt. The starting isonitriles are easily accessible, and commercially available aldehydes and fluoromethylation reagents serve as reaction partners. Functional group tolerance is high, as documented by the successful preparation of a series of 2,3-disubstituted indoles.

Fe-catalyzed Fukuyama-type indole synthesis triggered by hydrogen atom transfer

Fe, Co, and Mn hydride-initiated radical olefin additions have enjoyed great success in modern synthesis, yet the extension of other hydrogen radicalophiles instead of olefins remains largely elusive. Herein, we report an efficient Fe-catalyzed intramolecular isonitrile-olefin coupling reaction delivering 3-substituted indoles, in which isonitrile was firstly applied as the hydrogen atom acceptor in the radical generation step by MHAT. The protocol features low catalyst loading, mild reaction conditions, and excellent functional group tolerance.

Recent Advances on Photoinduced Cascade Strategies for the Synthesis of N-Heterocycles

Over the last decade, visible-light photocatalysis has proved to be a powerful tool for the construction of N-heterocyclic frameworks, important constituents of natural products, insecticides, pharmacologically relevant therapeutic agents and catalysts. This account highlights recent developments and established methods towards the photocatalytic cascades for preparation of different classes of N-heterocycles, giving emphasis on our contribution to the field.

Bifunctional acidic ionic liquid-catalyzed decarboxylative cascade synthesis of quinoxalines in water under ambient conditions

An acid-functionalized ionic liquid (IL)-catalyzed cascade decarboxylative cyclization of 2-arylanilines with α-oxocarboxylic acids was developed.

Merging CF3SO2Na photocatalysis with palladium catalysis to enable decarboxylative cross-coupling for the synthesis of aromatic ketones at room temperature

By merging CF₃SO₂Na-mediated photocatalysis with palladium catalysis, an efficient decarboxylative coupling strategy of α-keto acids and aryl boronic acids has been developed for the synthesis of aromatic ketones.

Radical Carbonylative Synthesis of Heterocycles by Visible Light Photoredox Catalysis

Visible light photocatalytic radical carbonylation has been established as a robust tool for the efficient synthesis of carbonyl-containing compounds. Acyl radicals serve as the key intermediates in these useful transformations and can be generated from the addition of alkyl or aryl radicals to carbon monoxide (CO) or various acyl radical precursors such as aldehydes, carboxylic acids, anhydrides, acyl chlorides or α-keto acids. In this review, we aim to summarize the impact of visible light-induced acyl radical carbonylation reactions on the synthesis of oxygen and nitrogen heterocycles. The discussion is mainly categorized based on different types of acyl radical precursors.

Photophysical properties and electron transfer photochemical reactivity of substituted phthalimides

Substituents on phthalimide affect its photophysics and photochemical reactivity. Electron donors generally result in low quantum yields of intersystem crossing and reactivity from singlet excited states.

Recent applications of Rose Bengal catalysis in N-heterocycles: a short review

The visible light harnessing ability of Rose Bengal, an organic dye, has been extensively employed in organic chemistry over the last few years. In visible light mediated reactions, this photoredox catalyst operates through multiple pathways and has the ability to provide distinctly different and valuable results. The most significant of these results are bond creation, bond functionalization, particularly for C–H and C–heteroatom bonds, and cross couplings. It is crucial to study these cases whenever these bond formations and couplings lead to the formation of heterocyclic compounds or their functionalization. The diverse biological activity and medicinal applications of heterocyclic compounds is an extensively explored area. This review primarily attempts to demonstrate the synthetic potential of Rose Bengal for synthesis and site selective functionalization of nitrogen containing heterocycles.

The recent applications of Rose Bengal as a photocatalyst for the synthesis and functionalization of N-heterocycles have been discussed.