Pauson–Khand reaction of fluorinated compounds

• Jorge Escorihuela,
• Daniel M. Sedgwick,
• Alberto Llobat,
• Mercedes Medio-Simón,
• Pablo Barrio and
• Santos Fustero

Beilstein J. Org. Chem. 2020, 16, 1662–1682, doi:10.3762/bjoc.16.138

• between an alkyne, an olefin and carbon monoxide, resulting in the regioselective formation of a cyclopentenone derivative (Scheme 1) [18][19][20][21][22]. This cobalt-mediated reaction was initially discovered by Pauson and Khand in the early 70s [23][24][25] and has since become a powerful

• are poor substrates for the PKR as they are deactivated in the cobalt-complexation step, and the highest yields are usually obtained with terminal alkynes. The scenario is similar in the case of fluorinated substrates, with the intramolecular version being much more developed than the intermolecular

• extrusion of two carbon monoxide ligands from the starting cobalt species, allowing the alkyne group to bind to the cobalt metal centers. The subsequent coordination of the olefin counterpart requires the extrusion of a third carbon monoxide ligand, leading to pentacarbonyl complex II. This highly

Oxime radicals: generation, properties and application in organic synthesis

• Igor B. Krylov,
• Stanislav A. Paveliev,
• Alexander S. Budnikov and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2020, 16, 1234–1276, doi:10.3762/bjoc.16.107

• endocyclic, high stereoselectivity was observed with the formation of trans-products (examples 106c and 108b). The oxidative cyclization of β,γ-unsaturated oximes 109 under the action of molecular oxygen and catalytic amounts of bis(5,5-dimethyl-1-(4-methylpiperazin-1-yl)hexane-1,2,4-trione)cobalt(II) (Co

Photocatalysis with organic dyes: facile access to reactive intermediates for synthesis

• Stephanie G. E. Amos,
• Marion Garreau,
• Luca Buzzetti and
• Jerome Waser

Beilstein J. Org. Chem. 2020, 16, 1163–1187, doi:10.3762/bjoc.16.103

• oxidation of 29.1 was achieved using Mes-Acr-Me+ (OD2) and a cobalt cocatalyst, ensuring an efficient dehydrogenation. Various N-heterocycles 29.3 were accessed via a radical cyclization cascade with the alkyne derivatives 29.2. Amidyl radical generation The oxidation of amides is more difficult compared to

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

• platform for dual catalysis due to their ability to promote both metallocatalysis and photocatalysis in a one-pot system [36][37][38][39]. Martin and co-workers carried out the C–O bond cleavage of alcohols using a cobalt porphyrin under visible light irradiation and a carbon monoxide atmosphere (Scheme 11

• ) [36]. The authors hypothesized that the C–O bond cleavage could be achieved via cobalt-mediated alcohol carbonylation followed by radical decarboxylation of the alkoxycarbonyl intermediate. In a proof-of-concept study, they proceeded with the carbonylation of 1-phenylethanol using Co(II) tetrakis(4

• tetrahydroquinolines by reductive quenching. Selenylation and thiolation of anilines. NiTPP as photoredox catalyst in oxidative and reductive quenching, in comparison with other photocatalysts. C–O bond cleavage of 1-phenylethanol using a cobalt porphyrin (CoTMPP) under visible light. Hydration of terminal alkynes by

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

• phenol 8 was generated by the reaction of 2-hydroxybenzaldehyde (5) and o‐phenylenediamine (7) at rt using a cobalt catalyst. In the next step, a benzimidazole-containing aldehyde 9 was obtained by the reaction of 6 with benzimidazole-substituted phenol 8. This ligand was immobilized on propylamine

Synthesis of triphenylene-fused phosphole oxides via C–H functionalizations

• Md. Shafiqur Rahman and
• Naohiko Yoshikai

Beilstein J. Org. Chem. 2020, 16, 524–529, doi:10.3762/bjoc.16.48

• via 1,4-cobalt migration. The resulting 7-hydroxybenzo[b]phosphole derivative was used for further π-extension through Suzuki–Miyaura couplings and a Scholl reaction, the latter closing the triphenylene ring. The absorption and emission spectra of the thus-synthesized compounds illustrated their

• characteristics of both triphenylene and benzo[b]phosphole. Results and Discussion The present synthetic study commenced with the recently reported preparation of 7-hydroxybenzo[b]phosphole derivative 3 from 3-(methoxymethoxy)phenylzinc (1), 5-decyne (2), and PhPCl2 in the presence of a cobalt–diphosphine

• catalyst (Scheme 2). This one-pot construction of the benzo[b]phosphole core ensured the preferential phosphole ring closure in proximity of the alkoxy group of the arylzinc reagent 1 (regioselectivity of ≈3:1), presumably due to a secondary interaction between the MOM group and the cobalt catalyst during

Visible-light-induced addition of carboxymethanide to styrene from monochloroacetic acid

• Kaj M. van Vliet,
• Nicole S. van Leeuwen,
• Albert M. Brouwer and
• Bas de Bruin

Beilstein J. Org. Chem. 2020, 16, 398–408, doi:10.3762/bjoc.16.38

• useful for the formation of new C–C bonds. Previous works from our group presented cobalt-catalyzed radical cyclization and carbonylation reactions [12][13][14][15][16]. Photoredox catalysis provides a way to generate radical intermediates from simple organic molecules by single-electron redox processes

Room-temperature Pd/Ag direct arylation enabled by a radical pathway

• Amy L. Mayhugh and
• Christine K. Luscombe

Beilstein J. Org. Chem. 2020, 16, 384–390, doi:10.3762/bjoc.16.36

• . There are limited examples across the aryl C–H functionalization literature indicating a transition metal-catalyzed radical process, limited largely to cobalt catalysis [31][32]. While there are several reports of palladium-catalyzed systems for room-temperature direct arylation (i.e., no directing

Recent developments in photoredox-catalyzed remote ortho and para C–H bond functionalizations

• Rafia Siddiqui and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 248–280, doi:10.3762/bjoc.16.26

• benzothiazoles via oxidant-free C–H thiolation: On the other hand, a novel dual photoredox catalytic system of photoredox catalyst 11 and a cobalt catalyst was designed by Wu and Lei for the construction of benzothiazoles [101]. Because of the properties of the photoredox catalyst 11, the reaction was carried

Combination of multicomponent KA² and Pauson–Khand reactions: short synthesis of spirocyclic pyrrolocyclopentenones

• Riccardo Innocenti,
• Elena Lenci,
• Gloria Menchi and
• Andrea Trabocchi

Beilstein J. Org. Chem. 2020, 16, 200–211, doi:10.3762/bjoc.16.23

• different compounds, such as (−)-kainic acid [51][52]. Previous similar approaches reported only planar pyrrolocyclopentenones starting from propargyl alcohol–cobalt complexes and allyl amides [50], or carbohydrate-derived allylpropargylamine [49] (Scheme 1a). Results and Discussion Cyclohexanone (1) and

• ). The acylation of the amino group was found necessary to allow for the cobalt-catalyzed reaction to proceed under a CO atmosphere. This step was also carried out in one pot after the KA2 reaction by diluting with pyridine and adding the acylating reagent, to achieve the corresponding product in

• –Khand reaction (Table 1, entry 13), possibly due to a coordinating effect towards the cobalt catalyst. Such an effect was confirmed when the N-tosylpiperidone was used as the ketone component, as also in this case the presence of the tosyl group impaired the acetylated KA2 adduct from reacting under

Extension of the 5-alkynyluridine side chain via C–C-bond formation in modified organometallic nucleosides using the Nicholas reaction

• Renata Kaczmarek,
• Dariusz Korczyński,
• James R. Green and
• Roman Dembinski

Beilstein J. Org. Chem. 2020, 16, 1–8, doi:10.3762/bjoc.16.1

• ]. In parallel, bioorganometallic chemistry provides new tools to influence biological interactions [16][17][18][19][20][21][22][23][24]. Cobalt possesses a diverse array of properties that can be manipulated to yield promising drug candidates [25]. The antiproliferative properties [26], as well as

• carbon monoxide-releasing properties [27][28] of dicobalt hexacarbonyl alkyne complexes have been noted, and their medicinal potential has been summarized [29][30][31]. Despite developments, the collection of metallo-nucleosides is limited. Hybridization of alkyl and aryl-substituted alkyne cobalt

• HeLa and K562 cell lines [31]. The formation of a reactive oxygen species in the presence of cobalt compounds was determined in K562 cells. The results indicate that the mechanism of action for most antiproliferative cobalt compounds may be related to the induction of oxidative stress [31

A review of asymmetric synthetic organic electrochemistry and electrocatalysis: concepts, applications, recent developments and future directions

• Munmun Ghosh,
• Valmik S. Shinde and
• Magnus Rueping

Beilstein J. Org. Chem. 2019, 15, 2710–2746, doi:10.3762/bjoc.15.264

• enzymes involve cobalt in the catalytically active center. In his article, Prof. Hisaeda reviewed vitamin B12-mediated electrochemical reactions in organic solvents in detail [83]. A number of pioneering results have been published in this area by leading electroorganic chemists [84][85][86]. In 1994 and

Recent advances in transition-metal-catalyzed incorporation of fluorine-containing groups

• Xiaowei Li,
• Xiaolin Shi,
• Xiangqian Li and
• Dayong Shi

Beilstein J. Org. Chem. 2019, 15, 2213–2270, doi:10.3762/bjoc.15.218

• different catalysts, such as palladium, copper, silver, iron, nickel, ruthenium, cobalt, etc. Palladium catalysis Palladium is a member of the nickel triad in the periodic table, and palladium complexes exist in three oxidation states, Pd(0), Pd(II), and Pd(IV). Straightforward interconversion between

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

Synthesis of acylglycerol derivatives by mechanochemistry

• Karen J. Ardila-Fierro,
• Andrij Pich,
• Marc Spehr,
• José G. Hernández and
• Carsten Bolm

Beilstein J. Org. Chem. 2019, 15, 811–817, doi:10.3762/bjoc.15.78

• -opening reaction of 2 with stearic acid (3a) was evaluated (Scheme 3a). Specifically, we focused on the use of Jacobsen cobalt(II)-salen complex (S,S)-cat (Scheme 3b), since similar salen complexes had originally been reported to facilitate epoxide ring-opening reactions with carboxylic acids as

• a promising one to mechanochemically access MAGs by ball milling. Experimentally, we attempted the cobalt-catalyzed epoxide ring-opening reaction by milling 2 with stearic acid (3a) in the presence of (S,S)-cat (2.5 mol %) and N,N-diisopropylethylamine (DIPEA; 1.0 equiv, Scheme 3a). Mechanistically

• ). However, purification of 4a by column chromatography on SiO2 favored acyl migration in 4a, thereby dropping the yield of 4a by increasing the amount of the isomeric sn-2,3-protected monoacylglycerol 4a’ (Figure 2) [42]. Typically, cobalt complex (S,S)-cat has been used for kinetic resolution of racemic

Design, synthesis and spectroscopic properties of crown ether-capped dibenzotetraaza[14]annulenes

• Krzysztof M. Zwoliński and
• Julita Eilmes

Beilstein J. Org. Chem. 2019, 15, 617–622, doi:10.3762/bjoc.15.57

• ], little research has been undertaken regarding DBTAAs functionalized with crown ether moieties (see Figure 1). Kruse and Breitmaier [24] reported annulated DBTAA‘s containing benzo-15-crown-5 scaffolds fused with benzenoid rings of the macrocyclic core. Both nickel(II) and cobalt(II) complexes were

• presence of alkali metal and ammonium ions. Sakata et al. reported the synthesis of peripherally functionalized DBTAAs with the two benzo-15-crown-5 scaffolds appended to the meso-benzoyl substituents [27]. Both crown ether-capped macrocycles in a form of free base and nickel(II) and cobalt(II) complexes

Selective benzylic C–H monooxygenation mediated by iodine oxides

• Kelsey B. LaMartina,
• Haley K. Kuck,
• Linda S. Oglesbee,
• Asma Al-Odaini and
• Nicholas C. Boaz

Beilstein J. Org. Chem. 2019, 15, 602–609, doi:10.3762/bjoc.15.55

• by Ishii and co-workers on the aerobic oxidation of cumene in acetic acid using catalytic NHPI and cobalt(II), resulted in a mixture of 2-phenyl-2-propanol, acetophenone, and phenol [60][61]. This lack of selectivity in the product was related in part to the propensity of the cumene hydroperoxide

Syntheses and chemical properties of β-nicotinamide riboside and its analogues and derivatives

• Mikhail V. Makarov and
• Marie E. Migaud

Beilstein J. Org. Chem. 2019, 15, 401–430, doi:10.3762/bjoc.15.36

• hexachloroacetone [28][71] or cobalt(II) acetate in the presence of hydrogen peroxide followed by removal of the cobalt cations with QuadraSil AP resin [60]. The nature of the counter anion vary as a function of the conditions applied. Reduction of N1-substituted 3-nicotinamide salts to the corresponding 1,4

• cobalt acetate in the presence of hydrogen peroxide. This approach required the subsequent removal of metal ions by Quadrasil resin. The oxidized acetonides 45 were subsequently deprotected using

Repurposing the anticancer drug cisplatin with the aim of developing novel Pseudomonas aeruginosa infection control agents

• Mingjun Yuan,
• Song Lin Chua,
• Yang Liu,
• Daniela I. Drautz-Moses,
• Joey Kuok Hoong Yam,
• Thet Tun Aung,
• Roger W. Beuerman,
• May Margarette Santillan Salido,
• Stephan C. Schuster,
• Choon-Hong Tan,
• Michael Givskov,
• Liang Yang and
• Thomas E. Nielsen

Beilstein J. Org. Chem. 2018, 14, 3059–3069, doi:10.3762/bjoc.14.284

• respective drug 3 times per day. Cornea wound was visualized by the aid of cobalt-blue filter equipped slit lamp biomicroscopy (New-generation Zoom clinical Slit Lamp, NS-2D, Righton), staining with Minims fluorescein sodium eye drops (Bausch and Lomb, 2% w/v) which is used in ophthalmology clinic for

Olefin metathesis catalysts embedded in β-barrel proteins: creating artificial metalloproteins for olefin metathesis

• Daniel F. Sauer,
• Johannes Schiffels,
• Takashi Hayashi,
• Ulrich Schwaneberg and
• Jun Okuda

Beilstein J. Org. Chem. 2018, 14, 2861–2871, doi:10.3762/bjoc.14.265

• catalyst or redox catalyst. Various metalloenzymes have been applied in laboratory-scale reactions and a few metalloenzymes such as nitrile hydratase (cobalt(III) in the active site) for the production of acrylamide have found application in industry [25]. Notably, however, the reaction scope of natural

Copolymerization of epoxides with cyclic anhydrides catalyzed by dinuclear cobalt complexes

• Yo Hiranoi and
• Koji Nakano

Beilstein J. Org. Chem. 2018, 14, 2779–2788, doi:10.3762/bjoc.14.255

• synthetic method for polyesters as the polymers’ architectures and properties can be easily controlled depending on the combination of two monomers. Thus, a variety of catalyst designs has been reported to prepare the desired copolymers efficiently. We herein report dinuclear cobalt–salen complexes with a

• benzene ring as a linker and their activities in copolymerization reactions. The dinuclear cobalt complexes showed a higher catalytic activity for the copolymerization of propylene oxide with phthalic anhydride than the corresponding mononuclear cobalt–salen complex and achieved one of the highest

• turnover frequencies ever reported. A variety of epoxides and CAs were also found to be copolymerized successfully by the dinuclear cobalt complex with a high catalytic activity. Keywords: cobalt; copolymerization; cyclic anhydrides; epoxides; polyesters; Introduction Aliphatic polyesters have received

Learning from B₁₂ enzymes: biomimetic and bioinspired catalysts for eco-friendly organic synthesis

• Keishiro Tahara,
• Ling Pan,
• Toshikazu Ono and
• Yoshio Hisaeda

Beilstein J. Org. Chem. 2018, 14, 2553–2567, doi:10.3762/bjoc.14.232

• Cobalamins (B12) are naturally occurring cobalt complexes with unique structures that play various important roles in vivo [1][2][3][4][5]. In B12, the cobalt center is coordinated by four equatorial pyrroles of the corrin ring and 2,3-dimethylbenzimidazole as a lower axial ligand (Figure 1a) [6][7][8]. The

• cobalamin with an upper ligand is termed vitamin B12 (a cyanide group), methylcobalamin (a methyl group), and adenosylcobalamin (an adenosyl group), respectively. The oxidation state of cobalt ions in B12 ranges from +1 to +3. Each oxidation state of cobalamins exhibits quite different ligand-accepting

• ligands of cobalt complexes 2 are superior to porphyrin ligands in terms of the model for the corrin framework of B12; both the imine/oxime-type and corrin ligands are monoanionic [57][58][59][60]. The imine/oxime-type cobalt complex 2 can be isolated in both the monoalkylated and dialkylated forms [59

Synthesis of aryl sulfides via radical–radical cross coupling of electron-rich arenes using visible light photoredox catalysis

• Amrita Das,
• Mitasree Maity,
• Simon Malcherek,
• Burkhard König and
• Julia Rehbein

Beilstein J. Org. Chem. 2018, 14, 2520–2528, doi:10.3762/bjoc.14.228

• triflates [8], and diazonium salts [9]. Typical metals used are palladium [10][11][12][13], copper [14][15][16][17][18][19][20][21], nickel [22][23][24], iron [25][26][27][28][29], cobalt [30][31][32], and rhodium [33][34]. Aryl sulfides are also synthesized by cross coupling of thiols and aryl Grignard

Cobalt- and rhodium-catalyzed carboxylation using carbon dioxide as the C1 source

• Tetsuaki Fujihara and
• Yasushi Tsuji

Beilstein J. Org. Chem. 2018, 14, 2435–2460, doi:10.3762/bjoc.14.221

• review, the Co- and Rh-catalyzed transformation of CO2 via carbon–carbon bond-forming reactions is summarized. Combinations of metals (cobalt or rhodium), substrates, and reducing agents realize efficient carboxylation reactions using CO2. The carboxylation of propargyl acetates and alkenyl triflates

• using cobalt complexes as well as the cobalt-catalyzed reductive carboxylation of α,β-unsaturated nitriles and carboxyamides in the presence of Et2Zn proceed. A Co complex has been demonstrated to act as an efficient catalyst in the carboxylation of allylic C(sp3)–H bonds. Employing zinc as the

• [2 + 2 + 2] cycloaddition of diynes and CO2 proceeds to afford pyrones. Keywords: carbon dioxide; carboxylation; cobalt; homogeneous catalysts; rhodium; Introduction Carbon dioxide (CO2) is one of the most important materials as renewable feedstock [1][2][3][4]. However, the thermodynamic and

A challenging redox neutral Cp*Co(III)-catalysed alkylation of acetanilides with 3-buten-2-one: synthesis and key insights into the mechanism through DFT calculations

• Andrew Kenny,
• Alba Pisarello,
• Arron Bird,
• Paula G. Chirila,
• Alex Hamilton and
• Christopher J. Whiteoak

Beilstein J. Org. Chem. 2018, 14, 2366–2374, doi:10.3762/bjoc.14.212

• not the C–H activation step, but instead and unexpectedly, effective competition with more stable compounds (resting states) not involved in the catalytic cycle. Keywords: acetanilides; alkylation; C–H activation; cobalt catalysis; DFT studies; Introduction Controlled functionalisation of ubiquitous

• application of these first-row transition metals stems from their low cost, ready availability and often wider reactivity profiles. One particular example which is currently attracting significant interest is cobalt, a metal which has found many applications in C–H functionalisation through exploitation of

• its diverse mechanisms [7]. Since 2013, the cobalt pre-catalysts, [Cp*Co(C6H6)](PF6)2 and [Cp*Co(CO)I2], have been successfully applied in a number of diverse C–H functionalisation protocols [8][9][10][11][12]. Whilst many of these protocols are very elegant, few examples are able to be applied to the