Photomechanochemistry: harnessing mechanical forces to enhance photochemical reactions

• Francesco Mele,
• Ana M. Constantin,
• Andrea Porcheddu,
• Raimondo Maggi,
• Giovanni Maestri,
• Nicola Della Ca’ and
• Luca Capaldo

Beilstein J. Org. Chem. 2025, 21, 458–472, doi:10.3762/bjoc.21.33

• mechanistic scenario than that operating in solution [71], where photogenerated thiyl radicals proved crucial intermediates. Parallelly, Hernández reported a photomechanochemical approach for the borylation of aryldiazonium salts in a ball milling apparatus equipped with a transparent polymethylmethacrylate

• content is not subject to CC BY 4.0 Photomechanochemical borylation of aryldiazonium salts. The photo in Scheme 8 was reproduced from [72] (© 2017 J. G. Hernández et al., published by Beilstein-Institut, distributed under the terms of the Creative Commons Attribution 4.0 International License, https

Advances in the use of metal-free tetrapyrrolic macrocycles as catalysts

• Mandeep K. Chahal

Beilstein J. Org. Chem. 2024, 20, 3085–3112, doi:10.3762/bjoc.20.257

• metal-free macrocycles for the C–H arylation of five-membered heteroarenes using aryldiazonium salts, with porphyrin serving as the photoredox catalyst [92]. Control experiments indicated that H2TPP (18), when irradiated with light, gave 80% yield of the C–H arylated product 77 for the reaction of furan

• of enol acetates with aryldiazonium salts [93]. The excitation of the porphyrin macrocycles by light irradiation initiated the catalytic cycle, generating aryl radicals from the diazonium salts, similar to findings by Gryko and co-workers. They explored both batch and continuous-flow photocatalysis

5th International Symposium on Synthesis and Catalysis (ISySyCat2023)

• Anthony J. Burke and
• Elisabete P. Carreiro

Beilstein J. Org. Chem. 2024, 20, 2704–2707, doi:10.3762/bjoc.20.227

• -dihydro-1H-pyrroles using aryldiazonium salts and (S)-PyraBox, followed by sequential Jones oxidation. They showcased their methodology by preparing both (R)-rolipram and (R)-baclofen hydrochloride. Tóth et al. reported the design and synthesis of new analogues of HeE1-2Tyr, a nonnucleoside SARS-CoV-2

Multicomponent syntheses of pyrazoles via (3 + 2)-cyclocondensation and (3 + 2)-cycloaddition key steps

• Ignaz Betcke,
• Alissa C. Götzinger,
• Maryna M. Kornet and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2024, 20, 2024–2077, doi:10.3762/bjoc.20.178

Carbonylative synthesis and functionalization of indoles

• Alex De Salvo,
• Raffaella Mancuso and
• Xiao-Feng Wu

Beilstein J. Org. Chem. 2024, 20, 973–1000, doi:10.3762/bjoc.20.87

• interesting method toward indole-3-yl aryl ketones was reported by Zhang et al. Considering the ability of the aryldiazonium salts to act as aryl radical source, in presence of the suitable metal catalyst or taking advantage of photocatalysis, they decided to perform a direct carbonylation of indoles with

Enantioselective synthesis of β-aryl-γ-lactam derivatives via Heck–Matsuda desymmetrization of N-protected 2,5-dihydro-1H-pyrroles

• Arnaldo G. de Oliveira Jr.,
• Martí F. Wang,
• Rafaela C. Carmona,
• Danilo M. Lustosa,
• Sergei A. Gorbatov and
• Carlos R. D. Correia

Beilstein J. Org. Chem. 2024, 20, 940–949, doi:10.3762/bjoc.20.84

• herein an enantioselective palladium-catalyzed Heck–Matsuda reaction for the desymmetrization of N-protected 2,5-dihydro-1H-pyrroles with aryldiazonium salts, using the chiral N,N-ligand (S)-PyraBox. This strategy has allowed straightforward access to a diversity of 4-aryl-γ-lactams via Heck arylation

• -lactam ring is a privileged scaffold widely present in drugs and natural products [12][13][14], as shown in Scheme 1. Herein, we report the effective desymmetrization strategy of N-protected 2,5-dihydro-1H-pyrroles using aryldiazonium salts and the chiral N,N-ligand (S)-PyraBox (Scheme 2). The obtained

• on our previous results regarding the desymmetrization of hidantoins [17], we started this study with the N-Boc-protected dihydropyrrole 1a using different electronic-demanding aryldiazonium salts and the standard reaction conditions for similar Heck–Matsuda reactions (Scheme 3), i.e., Pd(TFA)2 as

A visible-light-induced, metal-free bis-arylation of 2,5-dichlorobenzoquinone

• Pieterjan Winant and
• Wim Dehaen

Beilstein J. Org. Chem. 2021, 17, 2315–2320, doi:10.3762/bjoc.17.149

• Pieterjan Winant Wim Dehaen Molecular Design and Synthesis, Department of Chemistry, KU Leuven, Celestijnenlaan 200F, 3001 Leuven, Belgium 10.3762/bjoc.17.149 Abstract A metal-free protocol for the direct bis-arylation of 2,5-dichlorobenzoquinone with aryldiazonium salts is reported. The reactive

• , aryldiazonium salts have long played an essential role as radical precursors [20]. Their use in CH-arylation reactions of olefins, catalyzed by copper salts, was first published by Meerwein in 1939 [21]. Recently, we published a Meerwein arylation/cyclization sequence to benzofuropyridine derivatives in this

• journal [22]. Attempts at reducing aryldiazonium salts organocatalytically have also been successful [23][24][25][26]. Inspired by the seminal work by Sanford [27], König et al. [28] designed a simple and effective CH-arylation reaction combining diazonium chemistry with photoredox catalysis. By using

Application of the Meerwein reaction of 1,4-benzoquinone to a metal-free synthesis of benzofuropyridine analogues

• Rashmi Singh,
• Tomas Horsten,
• Rashmi Prakash,
• Swapan Dey and
• Wim Dehaen

Beilstein J. Org. Chem. 2021, 17, 977–982, doi:10.3762/bjoc.17.79

• polycyclic derivatives was designed. The procedures towards such polycyclic building blocks include C–H-arylation strategies. In the classical Meerwein reaction, aryldiazonium salts are used as the reagents to couple aryl groups to electron-poor alkenes, and this process is assumed to proceed via a free

• -radical mechanism [29]. Similar reaction intermediates can be prepared using precursors such as organoboron reagents [30]. However, due to the accessibility, aryldiazonium salts are the reagents of choice. They can be prepared starting from the commercially available corresponding anilines. The present

When metal-catalyzed C–H functionalization meets visible-light photocatalysis

• Lucas Guillemard and
• Joanna Wencel-Delord

Beilstein J. Org. Chem. 2020, 16, 1754–1804, doi:10.3762/bjoc.16.147

• transformation concerned the direct arylation of various aromatic compounds bearing different DGs with aryldiazonium salts (Figure 20). In her initial study in 2005, Sanford reported a similar arylation and diazonium salts were already identified as appropriate coupling partners. However, harsh reaction

• independently published alternative procedures based on the same dual catalytic system merging C–H activation and photoredox catalysis. In 2017, Xu’s group reported a variation of the ortho-arylation of acetanilides and benzamides with aryldiazonium salts [84], now compatible with a cheaper photosensitizer, i.e

• bicoordinating DGs to facilitate C(sp3)–H metalation, Polyzos’s group reported the direct arylation of aliphatic bonds with aryldiazonium salts via a palladium/photoredox dual catalysis (Figure 26) [88]. The method utilized an 8-aminoquinoline-derived bidentate auxiliary, and, in contrast with a vast majority of

Copper-based fluorinated reagents for the synthesis of CF₂R-containing molecules (R ≠ F)

• Louise Ruyet and
• Tatiana Besset

Beilstein J. Org. Chem. 2020, 16, 1051–1065, doi:10.3762/bjoc.16.92

• )aryldiazonium salts, a panel of difluoromethylated arenes and heteroarenes was obtained (26 examples, up to 84% yield). Note that the transformation was also carried out starting from 4-methoxyaniline followed by the in situ formation of the corresponding diazonium salt. In the same vein, the authors used this

• functionalization of alkyl bromides, alkyl mesylates, aryldiazonium salts [43] as well as electron-rich arenes [44] (Scheme 4). In 2015, the group of Qing investigated the oxidative difluoromethylation reaction of terminal alkynes with TMSCF2H via a copper-mediated reaction [45]. Using a stoichiometric amount of

• turned out to be functional group tolerant. The same group extended their protocol to the functionalization of aryldiazonium salts [79]. Very recently, a similar protocol was applied to the pentafluoroethylation of (hetero)aryl halides as well as alkenyl iodides derived from natural compounds (e.g

Recent applications of porphyrins as photocatalysts in organic synthesis: batch and continuous flow approaches

• Rodrigo Costa e Silva,
• Luely Oliveira da Silva,
• Aloisio de Andrade Bartolomeu,
• Timothy John Brocksom and
• Kleber Thiago de Oliveira

Beilstein J. Org. Chem. 2020, 16, 917–955, doi:10.3762/bjoc.16.83

• reported a metal-free photoarylation of five-membered heteroarenes with aryldiazonium salts and meso-arylated porphyrin derivatives as photoredox catalyst [11]. Compounds such as furan, thiophene, and N-Boc-pyrrole derivatives were obtained by this methodology in 29–81% yields (Scheme 3). The key-step of

• ). For an oxidative quenching, the photoarylation of heteroarenes and alkynes with aryldiazonium salts, and the oxidative decarboxylative coupling between cinnamic acid and tetrahydrofuran also showed better results when NiTPP was used instead of eosin [32][33][34] (Scheme 10). Regarding protocols

• for the alkylation of aldehydes with diazo acetates in the presence of TPP. Arylation of heteroarenes with aryldiazonium salts using TPFPP as photocatalyst, and corresponding mechanism. A) Scope with different aryldiazonium salts and enol acetates. B) Photocatalytic cycles and comparison between TPP

A systematic review on silica-, carbon-, and magnetic materials-supported copper species as efficient heterogeneous nanocatalysts in “click” reactions

• Pezhman Shiri and
• Jasem Aboonajmi

Beilstein J. Org. Chem. 2020, 16, 551–586, doi:10.3762/bjoc.16.52

• reflux conditions for one day. The resulting powder was filtered off, washed with methanol, and dried. Finally, excess copper was removed by the Soxhlet extraction method (Scheme 9). The 1,3-dipolar reaction of organic alkynes, organic bromides (or aryldiazonium salts or epoxides), and sodium azide

Copper-promoted/copper-catalyzed trifluoromethylselenolation reactions

• Clément Ghiazza and
• Anis Tlili

Beilstein J. Org. Chem. 2020, 16, 305–316, doi:10.3762/bjoc.16.30

• , this species is in an equilibrium with the −SeCF3 anion. As proposed by Hor and Weng, Deng and Xiao also suggested that CuSeCF3 was the active species in the mechanism. In 2016, the group of Rueping described a sequential copper-catalyzed selenocyanation of aryldiazonium salts, followed by

Synthesis of indolo[1,2-c]quinazolines from 2-alkynylaniline derivatives through Pd-catalyzed indole formation/cyclization with N,N-dimethylformamide dimethyl acetal

• Antonio Arcadi,
• Sandro Cacchi,
• Giancarlo Fabrizi,
• Francesca Ghirga,
• Antonella Goggiamani,
• Antonia Iazzetti and
• Fabio Marinelli

Beilstein J. Org. Chem. 2018, 14, 2411–2417, doi:10.3762/bjoc.14.218

• -catalyzed reaction of o-(o-aminophenylethynyl) trifluoroacetanilides 5 with aryl halides and aryldiazonium salts led to the formation of 12-arylindolo[1,2-c]quinazolin-6(5H)-ones 8 in moderate to excellent yields (Scheme 2a) [23]. Very likely, under these reaction conditions, the palladium-catalyzed

Cobalt bis(acetylacetonate)–tert-butyl hydroperoxide–triethylsilane: a general reagent combination for the Markovnikov-selective hydrofunctionalization of alkenes by hydrogen atom transfer

• Xiaoshen Ma and
• Seth B. Herzon

Beilstein J. Org. Chem. 2018, 14, 2259–2265, doi:10.3762/bjoc.14.201

• transfer (HAT) to the alkene substrate, followed by interception of the resulting alkyl radical intermediate with a SOMOphile. In addition, we report the first reductive couplings of unactivated alkenes and aryldiazonium salts by an HAT pathway. The simplicity and generality of the Co(acac)2–TBHP–Et3SiH

• properties were examined. These experiments revealed that this coupling is compatible with a broad range of functional groups and aryl substitution patterns (7d–j, 52–97%). The naphthylazo derivative 7k was obtained in 69% yield using 1-naphthyldiazonium tetrafluoroborate. However, aryldiazonium salts

• unactivated alkenes (H–X addition, X = H, F, Cl, Br, I, O, S, Se, N, and C). We have also reported the first reductive coupling reactions of alkenes and aryldiazonium salts under HAT conditions. These transformations proceed in high regioselectivity and efficiency. Further efforts will focus on expanding the

Synthesis of 9-arylalkynyl- and 9-aryl-substituted benzo[b]quinolizinium derivatives by Palladium-mediated cross-coupling reactions

• Siva Sankar Murthy Bandaru,
• Darinka Dzubiel,
• Heiko Ihmels,
• Mohebodin Karbasiyoun,
• Mohamed M. A. Mahmoud and
• Carola Schulzke

Beilstein J. Org. Chem. 2018, 14, 1871–1884, doi:10.3762/bjoc.14.161

• ] between the benzo[b]quinolizinium-9-trifluoroborate (3b) and aryldiazonium salts. We focused our attention on derivatives 1a–d because in these cases a direct comparison with the already reported synthesis with a Suzuki–Miyaura reaction is possible. As we are particularly interested in benzo[b

• conditions by the Pd-catalyzed Suzuki–Miyaura reaction of the aryldiazonium salts 4a–d with benzo[b]quinolizinium-9-trifluoroborate (3b). The latter substrate was obtained as analytically pure product in moderate yield by the reaction of benzo[b]quinolizinium-9-boronic acid (3a) [34] with NaBF4 (Scheme 1

• conditions to avoid the formation of hydroxide ions. To avoid the potential interference of bases, we attempted to improve of the conditions for the Suzuki–Miyaura coupling in the base-free variant using aryldiazonium reagents [39]. Although the coupling reactions between aryldiazonium salts and arylboronic

Progress in copper-catalyzed trifluoromethylation

• Guan-bao Li,
• Chao Zhang,
• Chun Song and
• Yu-dao Ma

Beilstein J. Org. Chem. 2018, 14, 155–181, doi:10.3762/bjoc.14.11

• substrate scope was still need to be expanded. Therefore, more efficient and practical methods were desirable. Trifluoromethylation of aryldiazonium salts (Sandmeyer type trifluoromethylation) Aromatic amines, which are available in great structural diversity, are prevalent chemicals in organic chemistry

CF₃SO₂X (X = Na, Cl) as reagents for trifluoromethylation, trifluoromethylsulfenyl-, -sulfinyl- and -sulfonylation. Part 1: Use of CF₃SO₂Na

• Hélène Guyon,
• Hélène Chachignon and
• Dominique Cahard

Beilstein J. Org. Chem. 2017, 13, 2764–2799, doi:10.3762/bjoc.13.272

• heterocycles. Subsequently, a photoredox-catalysed azotrifluoromethylation of unactivated alkenes was developed by Chen, Xiao and co-workers [32]. The scope was broad for a variety of unactivated alkenes, functionalised or not, and aryldiazonium salts (Scheme 13). Interestingly, the method did not require

Chiral phase-transfer catalysis in the asymmetric α-heterofunctionalization of prochiral nucleophiles

• Johannes Schörgenhumer,
• Maximilian Tiffner and
• Mario Waser

Beilstein J. Org. Chem. 2017, 13, 1753–1769, doi:10.3762/bjoc.13.170

• diazocarboxylates 38. Asymmetric α-fluorination of benzofuranones 4 using diazocarboxylates 38 in the presence of phosphonium salt PTC F1. Anionic phase-transfer-catalysed α-amination of β-ketoesters 1 with aryldiazonium salts 41. Triazolium salt L-catalysed α-amination of different prochiral nucleophiles with in

Mechanochemical borylation of aryldiazonium salts; merging light and ball milling

• José G. Hernández

Beilstein J. Org. Chem. 2017, 13, 1463–1469, doi:10.3762/bjoc.13.144

• Jose G. Hernandez Institute of Organic Chemistry, RWTH Aachen University, Landoltweg 1, D-52074 Aachen, Germany 10.3762/bjoc.13.144 Abstract Merging of photo- and mechanochemical activation permitted studying the role of eosin Y in the borylation of aryldiazonium salts in a ball mill

• –solvent charge-transfer complex formation. Keywords: aryldiazonium salts; borylation; eosin Y; mechanochemistry; photocatalysis; Introduction The use of mechanical force to process materials or to induce chemical transformations is perhaps as old as the history of mankind itself [1]. Similarly, from

• aforementioned context makes one wonder about the potential for conducting chemical reactions under simultaneous photo- and mechanical activation. To test this idea, the photocatalyzed borylation of aryldiazonium salts, first reported in solution by Yan and co-workers was selected as a model reaction [18]. In

Chemoselective synthesis of diaryl disulfides via a visible light-mediated coupling of arenediazonium tetrafluoroborates and CS₂

• Jing Leng,
• Shi-Meng Wang and
• Hua-Li Qin

Beilstein J. Org. Chem. 2017, 13, 903–909, doi:10.3762/bjoc.13.91

• and to minimize the formation of the byproducts was conducted. As recently surveyed, photoredox catalysts are widely employed for the generation of radicals for diverse radical reactions [19]. Further, the application of aryl radicals generated from aryldiazonium salts under visible light irradiation

Cationic Pd(II)-catalyzed C–H activation/cross-coupling reactions at room temperature: synthetic and mechanistic studies

• Takashi Nishikata,
• Alexander R. Abela,
• Shenlin Huang and
• Bruce H. Lipshutz

Beilstein J. Org. Chem. 2016, 12, 1040–1064, doi:10.3762/bjoc.12.99

• traditional Suzuki–Miyaura coupling. It is used to control a range of plant pathogens in broadacre and horticultural crops (Scheme 6) [207]. Felpin and co-workers have reported its synthesis starting from aryldiazonium salts [208], while the Heinrich group has employed a free-radical biaryl cross-coupling of

Pyridine-promoted dediazoniation of aryldiazonium tetrafluoroborates: Application to the synthesis of SF₅-substituted phenylboronic esters and iodobenzenes

• George Iakobson,
• Junyi Du,
• Alexandra M. Z. Slawin and
• Petr Beier

Beilstein J. Org. Chem. 2015, 11, 1494–1502, doi:10.3762/bjoc.11.162

• for an efficient reaction. Alkali metal acetates are known to facilitate decomposition of aryldiazonium salts by the formation of diazoacetates and diazo anhydrides, which decompose to aryl radicals [76]. These additives were used in Meerwein arylation of isopropenyl acetate [77]. In our case, two

• . Conducting the reaction on a gram scale proceeded without a notable loss of efficiency and the reaction can be performed in air (Table 2, entries 8–10). Pyridine is known to induce decomposition of aryldiazonium salts. Zollinger and Abramovitch studied the interaction of pyridine with aryldiazonium

• established that the hydrogen atom in the product comes exclusively from THF and not from pyridine or MeCN (Table 4). The observed deuterium enrichment using THF-d8 was around 80%. Thermal decomposition of aryldiazonium salts prepared from immobilized triazene precursors and the formation of deuterated