Pyridine C(sp²)–H bond functionalization under transition-metal and rare earth metal catalysis

• Haritha Sindhe,
• Malladi Mounika Reddy,
• Karthikeyan Rajkumar,
• Akshay Kamble,
• Amardeep Singh,
• Anand Kumar and
• Satyasheel Sharma

Beilstein J. Org. Chem. 2023, 19, 820–863, doi:10.3762/bjoc.19.62

• intact under the reaction conditions without any further oxidation. Different oxidants resulted in different products such as the monoarylated product 118 formed in the presence of TBHP as oxidant and the benzylated product 119 was obtained when potassium persulfate was used. Interestingly, aza-fluorene

• yields (Scheme 28). In this reaction, Grignard reagent 148 was used as arylation source in excess amount as the reagent underwent homocoupling leading to the formation of biaryl systems under the reaction conditions. 1,2-Dichloro-2-methylpropane (149) was found to be an effective oxidant under the

• the use of pyridines for the formation of quinolines and isoquinolines, an oxidant-dependent rhodium-catalyzed C–H annulation of pyridines with alkynes was reported by Li and co-workers [105] in 2011 for the direct synthesis of quinolines 180 and isoquinolines 181 involving a two-fold C–H activation

Sulfate radical anion-induced benzylic oxidation of N-(arylsulfonyl)benzylamines to N-arylsulfonylimines

• Joydev K. Laha,
• Pankaj Gupta and
• Amitava Hazra

Beilstein J. Org. Chem. 2023, 19, 771–777, doi:10.3762/bjoc.19.57

• with ortho-substituted anilines is also reported. The key features of the protocol include the use of a green oxidant, a short reaction time (30 min), chromatography-free isolation, scalability, and economical, delivering N-arylsulfonylimines in excellent yields of up to 96%. While the oxidation of N

• used as an additive along with the oxidant K2S2O8 in MeCN, the desired product N-benzenesulfonylimine 2a was obtained in 90% yield (Table 1, entry 3). Subsequently, we carried out further optimization studies by changing the additive, solvent, temperature, and reaction time to obtain the best possible

• -substituted anilines. The key features including the use of a green oxidant, a short reaction time, chromatography-free isolation, and scalability mark a distinction from the contemporary methods. Although we propose a dual role for SO4·− involving both hydrogen atom abstraction (HAT) and single electron

Honeycomb reactor: a promising device for streamlining aerobic oxidation under continuous-flow conditions

• Masahiro Hosoya,
• Yusuke Saito and
• Yousuke Horiuchi

Beilstein J. Org. Chem. 2023, 19, 752–763, doi:10.3762/bjoc.19.55

• , which diminishes the atom economy [2]. To overcome this limitation, the use of molecular oxygen (O2) present in air as an oxidant is one of the ideal solutions [10][11]. The reduction of O2 generates only water as a byproduct, leading to high atom-economy processes. However, the use of O2 as an oxidant

Transition-metal-catalyzed domino reactions of strained bicyclic alkenes

• Austin Pounder,
• Eric Neufeld,
• Peter Myler and
• William Tam

Beilstein J. Org. Chem. 2023, 19, 487–540, doi:10.3762/bjoc.19.38

Transition-metal-catalyzed C–H bond activation as a sustainable strategy for the synthesis of fluorinated molecules: an overview

• Louis Monsigny,
• Floriane Doche and
• Tatiana Besset

Beilstein J. Org. Chem. 2023, 19, 448–473, doi:10.3762/bjoc.19.35

• the presence of an electrophilic source or an oxidation/ligand exchange in the presence of a nucleophilic source (i.e., AgSCF3) and an oxidant (B in Scheme 4). Finally, after a reductive elimination step, the expected functionalized product 6 is obtained and the palladium catalyst is regenerated. In

• year, the group of Huang reported an elegant and straightforward palladium(II)-catalyzed ortho-selective trifluoromethylthiolation of arenes bearing various directing groups using the nucleophilic trifluoromethylthiolating source AgSCF3 in combination with Selectfluor® as oxidant (Scheme 6, 29 examples

• . Note that, in this process, Selectfluor® is playing a key role. Indeed, using this electrophilic fluorinating source as oxidant generates a Pd(IV)(ppy)F(OAc)2 (ppy = 2-phenylpyridine) complex as intermediate. As the competitive C–F bond formation was disfavored (slow reductive elimination step), the

Synthesis and reactivity of azole-based iodazinium salts

• Thomas J. Kuczmera,
• Annalena Dietz,
• Andreas Boelke and
• Boris J. Nachtsheim

Beilstein J. Org. Chem. 2023, 19, 317–324, doi:10.3762/bjoc.19.27

• -chloroperoxybenzoic acid (mCPBA) as the oxidant of choice in the presence of triflic acid (TfOH) [27][29]. Based on these promising results, the conditions were optimized using o-benzimidazole-substituted iodoarenes 4aa and 4ah (Table 1). While running the reaction in MeCN as solvent resulted in no product formation

• TsNH2 in combination with NaOCl as an oxidant was investigated next. Under these conditions, the N-Me salts 5ax and 12 gave the desired products 14a and 14b in 55% and 26% yield, respectively. The corresponding N-Ph- and N-Mes-derivatives 5ay and 5az failed to give products 14c and 14d and only

An efficient metal-free and catalyst-free C–S/C–O bond-formation strategy: synthesis of pyrazole-conjugated thioamides and amides

• Shubham Sharma,
• Dharmender Singh,
• Sunit Kumar,
• Vaishali,
• Rahul Jamra,
• Naveen Banyal,
• Deepika,
• Chandi C. Malakar and
• Virender Singh

Beilstein J. Org. Chem. 2023, 19, 231–244, doi:10.3762/bjoc.19.22

• , metal-free and easy to perform reaction conditions. Moreover, the pyrazole C-3/5-linked amide conjugates were also synthesized via an oxidative amination of pyrazole carbaldehydes and 2-aminopyridines using hydrogen peroxide as an oxidant. Keywords: C–S/O bond formation; metal-free; oxidative amidation

• yield was observed (entries 2–5, Table 2). The oxidant TBHP (10 equiv) failed to deliver the anticipated product in good yield (36%, entry 6, Table 2). Similar results were obtained with H2O2 (25.0 equiv) under neat reaction conditions (entry 7, Table 2). Next, we performed the oxidative amidation

• available substituted 2-aminopyridines and hydrogen peroxide as an oxidant. The biological evaluation of the thioamide and amide conjugates is underway in our laboratory. Experimental General information All chemicals and reagents were purchased from Sigma-Aldrich, Acros, Avera Synthesis, Spectrochem Pvt

Identification and determination of the absolute configuration of amorph-4-en-10β-ol, a cadinol-type sesquiterpene from the scent glands of the African reed frog Hyperolius cinnamomeoventris

• Angelique Ladwig,
• Markus Kroll and
• Stefan Schulz

Beilstein J. Org. Chem. 2023, 19, 167–175, doi:10.3762/bjoc.19.16

• synthesis by Taber that used dichromate as an oxidant [13] led to a less diastereoselective reaction furnishing the three ketones 9, 10, and 11 in a ratio of 36:2:5. The cis-conformation of the decalin backbone of 9 and 11 originates from the endo-selectivity of the Diels–Alder reaction and the boat

Combining the best of both worlds: radical-based divergent total synthesis

• Kyriaki Gennaiou,
• Antonios Kelesidis,
• Maria Kourgiantaki and
• Alexandros L. Zografos

Beilstein J. Org. Chem. 2023, 19, 1–26, doi:10.3762/bjoc.19.1

• generation of radicals from carbonyl reduction [18] but also manganese(III) acetate as a convenient one-electron oxidant [19]. The next twenty years, the field continued to flourish mainly by way of the decipherment of hydrogen atom transfer (HAT) mechanisms, which led to the establishment of several

• nucleophile is employed, radical 223 is favored, leading to either monosubstitution or disubstitution with external nucleophiles, depending on the presence of oxidant or reductant in the reaction mixture. Based on this plan, Zhu’s group managed to synthesize a rich number of lignans and congeners, such as

Synthetic study toward tridachiapyrone B

• Morgan Cormier,
• Florian Hernvann and
• Michaël De Paolis

Beilstein J. Org. Chem. 2022, 18, 1741–1748, doi:10.3762/bjoc.18.183

• necessary (70% yield, 2:1 dr). The desaturation of the enone compound was next examined and while exposure of 13 to oxidant (o-iodoxybenzoic acid (IBX) or 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)) left the starting materials unchanged, treatment with NaH in the presence of oxygen to induce the

Redox-active molecules as organocatalysts for selective oxidative transformations – an unperceived organocatalysis field

• Elena R. Lopat’eva,
• Igor B. Krylov,
• Dmitry A. Lapshin and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2022, 18, 1672–1695, doi:10.3762/bjoc.18.179

• organocatalyst does not undergo oxidation or reduction but facilitates interaction between oxidant and substrate (Scheme 1, type II organocatalysis) are fluently discussed below to show the fundamental difference between type II and type III redox-organocatalysis. Organocatalysis by activation of redox

• ethanol). Brønsted acid catalysis by TsOH was also employed in a selective sulfoxidation employing PhI(OAc)2 as oxidant [69]. In this case another mode of catalysis was proposed, including the covalent bonding of the acid catalyst anion and the oxidant with the formation of PhI(OTs)OH as the catalytically

• homogeneous process, which once initiated on the TiO2 surface, can produce multiple molecules of product without additional light absorption. Another approach to the generation of imide-N-oxyl radicals under mild conditions without transition metal salts as co-catalysts employs electric current as the oxidant

Functionalization of imidazole N-oxide: a recent discovery in organic transformations

• Koustav Singha,
• Imran Habib and
• Mossaraf Hossain

Beilstein J. Org. Chem. 2022, 18, 1575–1588, doi:10.3762/bjoc.18.168

• presence of 1.0 mmol AcCl as eliminating agent (EA) in dry THF as solvent at −78 °C; (II) in case of path B, the mixture of 1.0 mmol of 2,2-dimethyl-4-phenyl-2H-imidazole 1-oxide (9a) and 1.0 mmol of pentafluorobenzene (12), 1.1 mmol of n-BuLi as base, 1.5 equiv DDQ as oxidant in dry THF as solvent was

• leaving groups. The eliminating agent (AcCl) led to O-acylation of the intermediate 14 and resulted in deoxygenation through the release of AcOH giving 2H-imidazole derivatives. On the other hand, in case of “addition–oxidation” (SNH AO, path B), the oxidant DDQ picked up a proton from intermediate 14 to

Dissecting Mechanochemistry III

• Lars Borchardt and
• José G. Hernández

Beilstein J. Org. Chem. 2022, 18, 1454–1456, doi:10.3762/bjoc.18.150

• an appropriate oxidant for C–N couplings towards the synthesis of 1,2-disubstituted benzimidazoles and quinazolin-4(3H)-one derivatives under mechanochemical conditions, as evidenced by Mal and co-workers (Scheme 5) [9]. However, the findings within Mechanochemistry III span beyond the synthesis or

• intermolecular C–N coupling reactions using DDQ as an oxidant.

Sinensiols H–J, three new lignan derivatives from Selaginella sinensis (Desv.) Spring

• Qinfeng Zhu,
• Beibei Gao,
• Qian Chen,
• Tiantian Luo,
• Guobo Xu and
• Shanggao Liao

Beilstein J. Org. Chem. 2022, 18, 1410–1415, doi:10.3762/bjoc.18.146

• treatment of cholecystitis, hepatitis, nephritis, eczema and bleeding [6]. Previous phytochemical studies showed the presence of flavonoids, lignans, glucosides and pigments in the plant [7][8] while pharmacological evaluations showed that some of the compounds possessed anti-oxidant and antiviral

Synthesis of meso-pyrrole-substituted corroles by condensation of 1,9-diformyldipyrromethanes with pyrrole

• Baris Temelli and
• Pinar Kapci

Beilstein J. Org. Chem. 2022, 18, 1403–1409, doi:10.3762/bjoc.18.145

• , pyrrole ratio, reaction time, catalyst type, and oxidant are important parameters on the yields of the reactions [28][29][30][31][32]. For this reason, optimization studies were carried out on these parameters. Based on the results of the preliminary studies, optimization studies were carried out in the

• the reaction time before the oxidant addition on the yield of product was investigated at −20 °C in 40 equivalents of pyrrole. When the reaction time was 1 hour, the yield decreased to 4% (Table 1, entry 8). If the reaction time exceeded 2 hours, unexpectedly no desired product was found at all (Table

• further increase in the amount of catalyst did not affect the yield (Table 1, entries 11–13). In order to determine the effect of the oxidant type and the oxidant amount, reactions were carried out with 3 and 4 equivalents of DDQ and p-chloranil. While more than 2 equivalents of DDQ did not have a

A one-pot electrochemical synthesis of 2-aminothiazoles from active methylene ketones and thioureas mediated by NH₄I

• Shang-Feng Yang,
• Pei Li,
• Zi-Lin Fang,
• Sen Liang,
• Hong-Yu Tian,
• Bao-Guo Sun,
• Kun Xu and
• Cheng-Chu Zeng

Beilstein J. Org. Chem. 2022, 18, 1249–1255, doi:10.3762/bjoc.18.130

• -alanine-assisted one-pot electrochemical synthesis of 2-aminothiazoles from active methylene ketones and thioureas mediated by NH4I (Scheme 1d). This electrochemical method features external-oxidant-free conditions and avoids the prefunctionalization of the substrates. Results and Discussion To

• and to determine the possible active intermediates involved, several control experiments were carried out. As shown in Scheme 4, when molecular iodine was employed as oxidant, the desired product 3a was obtained in a 67% yield under otherwise identical conditions (Scheme 4a), but without passing

Derivatives of benzo-1,4-thiazine-3-carboxylic acid and the corresponding amino acid conjugates

• Péter Kisszékelyi,
• Tibor Peňaška,
• Klára Stankovianska,
• Mária Mečiarová and
• Radovan Šebesta

Beilstein J. Org. Chem. 2022, 18, 1195–1202, doi:10.3762/bjoc.18.124

• successfully prepared [32]. The protocol, using NaI as a catalyst and K2S2O8 as an oxidant, tolerated a broad range of substrates with good stereoselectivity. Interestingly, structurally related benzothiazine derivatives with a carboxylic function in the C-3 position are only seldomly described in the

A Streptomyces P450 enzyme dimerizes isoflavones from plants

• Run-Zhou Liu,
• Shanchong Chen and
• Lihan Zhang

Beilstein J. Org. Chem. 2022, 18, 1107–1115, doi:10.3762/bjoc.18.113

• activity was assayed using a Total Antioxidant Capacity Assay Kit with ABTS method (Beyotime Biotechnology). Briefly, the fresh ABTS working solution was prepared by mixing ABTS stock solution with oxidant solution for an overnight reaction, and then this mixture was diluted 50 times by 80% ethanol. To

Radical cation Diels–Alder reactions of arylidene cycloalkanes

• Kaii Nakayama,
• Hidehiro Kamiya and
• Yohei Okada

Beilstein J. Org. Chem. 2022, 18, 1100–1106, doi:10.3762/bjoc.18.112

• methods [19][20][21][22][23][24][25][26][27][28][29][30][31][32]. A one electron oxidant can also be an initiator for this transformation [33][34][35]. Overall, the scope of the reaction has been expanding. Starting from trans-anethole, several functionalities at the β-position are found to be compatible

Electrochemical formal homocoupling of sec-alcohols

• Kosuke Yamamoto,
• Kazuhisa Arita,
• Masashi Shiota,
• Masami Kuriyama and
• Osamu Onomura

Beilstein J. Org. Chem. 2022, 18, 1062–1069, doi:10.3762/bjoc.18.108

• ]. Electroorganic chemistry has been recognized as an environmentally benign and powerful strategy to promote redox reactions using electricity as a traceless oxidant or reductant [24][25][26][27][28]. Electrochemical pinacol coupling would be a promising alternative to avoid the use of low-valent metal reductants

Electrochemical vicinal oxyazidation of α-arylvinyl acetates

• Yi-Lun Li,
• Zhaojiang Shi,
• Tao Shen and
• Ke-Yin Ye

Beilstein J. Org. Chem. 2022, 18, 1026–1031, doi:10.3762/bjoc.18.103

• diverse α-azidoketones in good yields without the use of a stoichiometric amount of chemical oxidant. A range of functionality is shown to be compatible with this transformation, and further applications are demonstrated. Keywords: azide; azidoketone; electrosynthesis; enol acetate; radical

• have reported a manganese dioxide-catalyzed radical azidation of enol acetates to afford the corresponding azidoketones using dioxygen as the oxidant (Scheme 1A) [14]. The adoption of electrosynthesis in green and sustainable redox transformations has been experiencing a dynamic renaissance [15][16][17

First example of organocatalysis by cathodic N-heterocyclic carbene generation and accumulation using a divided electrochemical flow cell

• Daniele Rocco,
• Ana A. Folgueiras-Amador,
• Richard C. D. Brown and
• Marta Feroci

Beilstein J. Org. Chem. 2022, 18, 979–990, doi:10.3762/bjoc.18.98

• giving esters 3a–c, formation of enoate byproducts 4a and 4b invoke the involvement of an external chemical oxidant species as cinnamaldehyde is added to the cathode chamber after the electrolysis has been stopped. The presence of byproducts 4a and 4b is most likely accounted for by the presence of

Synthesis of odorants in flow and their applications in perfumery

• Merlin Kleoff,
• Paul Kiler and
• Philipp Heretsch

Beilstein J. Org. Chem. 2022, 18, 754–768, doi:10.3762/bjoc.18.76

• oxidant (Scheme 8B) [39]. The process is performed at 120 °C at 10 bar with a residence time of 6 min, and catalyzed homogenously utilizing the established “MC-system” (manganese/cobalt/bromide) in a heated tube reactor. Remarkably, acetophenone is obtained in a good yield of 66% and in 96% purity without

Rapid gas–liquid reaction in flow. Continuous synthesis and production of cyclohexene oxide

• Kyoko Mandai,
• Tetsuya Yamamoto,
• Hiroki Mandai and
• Aiichiro Nagaki

Beilstein J. Org. Chem. 2022, 18, 660–668, doi:10.3762/bjoc.18.67

• Medical Science, Nijigaoka, Kani-city, Gifu Prefecture, 509-0293, Japan 10.3762/bjoc.18.67 Abstract The enhanced reaction rate in the epoxidation of cyclohexene with air as an oxidant was discovered without any added catalyst utilizing a continuous flow reactor constructed with readily available

DDQ in mechanochemical C–N coupling reactions

• Shyamal Kanti Bera,
• Rosalin Bhanja and
• Prasenjit Mal

Beilstein J. Org. Chem. 2022, 18, 639–646, doi:10.3762/bjoc.18.64

• -Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) is a commonly known oxidant. Herein, we report that DDQ can be used to synthesize 1,2-disubstituted benzimidazoles and quinazolin-4(3H)-ones via the intra- and intermolecular C–N coupling reaction under solvent-free mechanochemical (ball milling) conditions. In

• as C–P [17], C–O [18][19][20], and C–S [21] were achieved using DDQ as an oxidant [22][23]. In addition, the utilization of DDQ as a photoredox catalyst [24] and co-catalyst [25][26] have also been documented in organic synthesis [27]. DDQ-mediated oxidative C–N cross-coupling reactions are well

• reagents, but none of them gave better yields (Table 1, entries 4–7). On the other hand, oxone as an oxidant yielded product 2a with up to 43% yield (Table 1, entry 8). Similarly, we have optimized the reaction conditions for the synthesis of 2-phenylquinazolin-4(3H)-one (5a) from anthranilamide and