Redox activated amines in the organophotoinduced alkylation of coumarins

Singh, Shashank; Tripathi, Krishna N.; Singh, Ravi P.

doi:10.1039/d2ob00943a

Cited by 7 publications

(4 citation statements)

References 61 publications

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“…Recently, Singh et al . reported the alkylation of coumarin‐3‐carboxylates by photocatalysis [13a,b] . Subsequently, Roy et al reported the alkylation of coumarin‐3‐carboxylates through a ligand‐to‐metal charge transfer (LMCT) approach by Lewis acid catalysis [13c] …”

Section: Introductionmentioning

confidence: 99%

Visible Light‐Induced Metal‐free Arylation of Coumarin‐3‐carboxylates with Arylboronic Acids

Banik,

Saikiran,

Permula

et al. 2024

Chemistry An Asian Journal

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The present work reports a novel methodology for the selective arylation of coumarin‐3‐carboxylates with arylboronic acids via a photochemical route, marking the first‐ever attempt for the direct alkenyl C‐H arylation using rose bengal as a photocatalyst, which is a readily available and cost‐effective alternative to transition metal catalysis. The reaction proceeds smoothly in MeOH/H2O solvent media in the presence of radical initiator affording the arylated products in good yields (60‐80%). The reaction parameters such as visible light, radical initiator, oxidant, anhydrous solvent, and inert atmosphere play a crucial role for the success of this methodology. The substituents present on the substrate show a significant effect on the conversion. This study provides a valuable contribution to the field of organic synthesis offering a new and efficient approach to the arylation of coumarin‐3‐carboxylic acid esters with a broad substrate scope and high functional group tolerance. It is a versatile method and provides a direct access to biologically relevant 4‐arylcoumarin‐3‐carboxylates.

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Section: Introductionmentioning

confidence: 99%

Visible Light‐Induced Metal‐free Arylation of Coumarin‐3‐carboxylates with Arylboronic Acids

Banik,

Saikiran,

Permula

et al. 2024

Chemistry An Asian Journal

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“…The emergence of photoredox chemistry in recent years was pioneered by the introduction of photocatalysts (PC) based on metals such as Ru and Ir [1][2][3][4][5][6]. However, due to the high cost and limited availability of precious metals, organic photocata-lysts have become a focal point of academic and industrial research [7][8][9][10][11][12][13][14][15]. Most of the established organic catalysts (acridinium salts [16][17][18][19], cyanoarenes [8,[20][21][22], quinones [23,24], etc.)…”

Section: Introductionmentioning

confidence: 99%

Mechanistic investigations of polyaza[7]helicene in photoredox and energy transfer catalysis

Rocker,

Zähringer,

Schmitz

et al. 2024

Beilstein J. Org. Chem.

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Organic photocatalysts frequently possess dual singlet and triplet photoreactivity and a thorough photochemical characterization is essential for efficient light-driven applications. In this article, the mode of action of a polyazahelicene catalyst (Aza-H) was investigated using laser flash photolysis (LFP). The study revealed that the chromophore can function as a singlet-state photoredox catalyst in the sulfonylation/arylation of styrenes and as a triplet sensitizer in energy transfer catalysis. The singlet lifetime is sufficiently long to exploit the exceptional excited state reduction potential for the activation of 4-cyanopyridine. Photoinduced electron transfer generating the radical cation was directly observed confirming the previously proposed mechanism of a three-component reaction. Several steps of the photoredox cycle were investigated separately, providing deep insights into the complex mechanism. The triplet-excited Aza-H, which was studied with quantitative LFP, is formed with a quantum yield of 0.34. The pronounced triplet formation was exploited for the isomerization reaction of (E)-stilbene to the Z-isomer and the cyclization of cinnamyl chloride. Catalyst degradation mainly occurs through the long-lived Aza-H triplet (28 µs), but the photostability is greatly increased when the triplet efficiently reacts in a catalytic cycle such that turnover numbers exceeding 4400 are achievable with this organocatalyst.

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“…Visible-light induced reactions have attracted extensive attention because of the advantages such as environmental friendliness, operational simplicity, and sustainability. , Aldehyde C–H bonds can be cleaved by hydrogen abstraction by radical species to generate acyl radicals. Such a radical-mediated S H 2 (homolytic bimolecular substitution) type hydrogen atom transfer (HAT) has excellent potential for site-selectivity .…”

Section: Introductionmentioning

confidence: 99%

Visible Light-Induced Cross-Dehydrocoupling of 3-Cyanocoumarins with Unactivated Aliphatic Aldehydes Enables Access to 4-Acylated Coumarins

Qian

Guan

2023

J. Org. Chem.

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We report visible light-induced cross-dehydrocoupling of 3-cyanocoumarins with unactivated aliphatic aldehydes for the direct synthesis of 4-acylated coumarins. Inexpensive and readily available (n-Bu)4NBr was used as a precursor of the hydrogen atom transfer (HAT) catalyst and [Ir(ppy)2(dtbbpy)PF6] as a photocatalyst. A variety of aldehydes including linear, branched, cyclic, and α,β-unsaturated aliphatic aldehydes were suitable for this reaction yielding the desired acylated coumarin derivatives in 41–98% yields. This method provides a mild, atom-economical, and environmentally friendly synthetic route for the direct acylation of 3-cyanocoumarins. This is the first example so far of C-4 aliphatic acylation of coumarins.

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Redox activated amines in the organophotoinduced alkylation of coumarins

Abstract: A metal-free photoinduced deaminative strategy for C-4 alkylation of coumarins using redox activated secondary and benzylic amine derived Katritzky pyridinium salts has been established and demonstrated efficiently.

Cited by 7 publications

References 61 publications

Visible Light‐Induced Metal‐free Arylation of Coumarin‐3‐carboxylates with Arylboronic Acids

Visible Light‐Induced Metal‐free Arylation of Coumarin‐3‐carboxylates with Arylboronic Acids

Mechanistic investigations of polyaza[7]helicene in photoredox and energy transfer catalysis

Visible Light-Induced Cross-Dehydrocoupling of 3-Cyanocoumarins with Unactivated Aliphatic Aldehydes Enables Access to 4-Acylated Coumarins

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