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

Bioinspired cobalt cubanes with tunable redox potentials for photocatalytic water oxidation and CO₂ reduction

• Zhishan Luo,
• Yidong Hou,
• Jinshui Zhang,
• Sibo Wang and
• Xinchen Wang

Beilstein J. Org. Chem. 2018, 14, 2331–2339, doi:10.3762/bjoc.14.208

• reactions. Keywords: CO2 reduction; cobalt cubane; photocatalysis; water oxidation; water splitting; Introduction The direct conversion of solar energy into chemical fuels (e.g., H2, CO and hydrocarbons) through water splitting and carbon fixation reactions is a sustainable solution to environmental

• Mn4CaO5 cubane of oxygen-evolving complex in photosystem II, there is an emerging number of molecular cubanes with metallic and heterobimetallic cores that are designed and synthesized for photosynthesis and electrochemistry. Cobalt-based molecular catalysts [44], in particular the ones containing a

• oxidation over 1-R is much higher than that over Co2+ ions, which may be due to the effect of the ligand for enhancing the stability of the entire cobalt metal center [48][49]. Furthermore, a long time course of water oxidation for 1-CN and Co2+ are also compared in Figure 6. It is obvious that the overall

Hydroarylations by cobalt-catalyzed C–H activation

• Rajagopal Santhoshkumar and
• Chien-Hong Cheng

Beilstein J. Org. Chem. 2018, 14, 2266–2288, doi:10.3762/bjoc.14.202

• Rajagopal Santhoshkumar Chien-Hong Cheng Department of Chemistry, National Tsing Hua University, Taiwan 10.3762/bjoc.14.202 Abstract As an earth-abundant first-row transition metal, cobalt catalysts offer a broad range of economical methods for organic transformations via C–H activation. One of

• the transformations is the addition of C–H to C–X multiple bonds to afford alkylation, alkenation, amidation, and cyclization products using low- or high-valent cobalt catalysts. This hydroarylation is an efficient approach to build new C–C bonds in a 100% atom-economical manner. In this review, the

• recent developments of Co-catalyzed hydroarylation reactions and their mechanistic studies are summarized. Keywords: catalysis; C−C formation; C–H activation; cobalt; hydroarylation; Introduction For the last three decades, atom-economical synthetic approaches have played a substantial role in organic

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

• Xiaoshen Ma Seth B. Herzon Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States Department of Pharmacology, Yale School of Medicine, New Haven, Connecticut 06520, United States 10.3762/bjoc.14.201 Abstract We show that cobalt bis(acetylacetonate) [Co(acac)2], tert

• -butyl hydroperoxide (TBHP), and triethylsilane (Et3SiH) constitute an inexpensive, general, and practical reagent combination to initiate a broad range of Markovnikov-selective alkene hydrofunctionalization reactions. These transformations are believed to proceed by cobalt-mediated hydrogen atom

• corresponding metal alkyl complex. This radical then undergoes addition to a second reagent (SOMOphile) to form the functionalized product (Scheme 1). A wide range of manganese, cobalt, or iron-based complexes containing diverse supporting ligands have found use in these reactions. To the best of our knowledge

Cobalt-catalyzed peri-selective alkoxylation of 1-naphthylamine derivatives

• Jiao-Na Han,
• Cong Du,
• Xinju Zhu,
• Zheng-Long Wang,
• Yue Zhu,
• Zhao-Yang Chu,
• Jun-Long Niu and
• Mao-Ping Song

Beilstein J. Org. Chem. 2018, 14, 2090–2097, doi:10.3762/bjoc.14.183

• Jiao-Na Han Cong Du Xinju Zhu Zheng-Long Wang Yue Zhu Zhao-Yang Chu Jun-Long Niu Mao-Ping Song College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou 450001, People’s Republic of China 10.3762/bjoc.14.183 Abstract A cobalt-catalyzed C(sp2)–H alkoxylation of 1

• system. Moreover, a series of biologically relevant fluorine-aryl ethers were easily obtained under mild reaction conditions after the removal of the directing group. Keywords: alkoxylation; C–H activation; cobalt catalysis; 1-naphthylamines; secondary alcohols; Introduction Aryl ethers are common

• systems. Recently, the inexpensive cobalt catalysts have received significant attention because of their unique and versatile activities in the C–H functionalizations [43][44][45][46][47][48][49][50][51]. In 2015, the cobalt-catalyzed alkoxylation of aromatic (and olefinic) carboxamides with primary

Cobalt-catalyzed nucleophilic addition of the allylic C(sp³)–H bond of simple alkenes to ketones

• Tsuyoshi Mita,
• Masashi Uchiyama,
• Kenichi Michigami and
• Yoshihiro Sato

Beilstein J. Org. Chem. 2018, 14, 2012–2017, doi:10.3762/bjoc.14.176

• Tsuyoshi Mita Masashi Uchiyama Kenichi Michigami Yoshihiro Sato Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo 060-0812, Japan 10.3762/bjoc.14.176 Abstract We herein describe a cobalt/Xantphos-catalyzed regioselective addition of simple alkenes to acetophenone derivatives

• bonds; cobalt; ketones; Introduction The cleavage of C–H bonds of unreactive hydrocarbon followed by functionalization should be an ideal method for constructing complex molecules without introduction of reactive functionality in advance [1][2][3][4][5][6][7][8][9]. Since terminal alkenes including α

• tautomerized to η1-allylcobalt(III) III by the assistance of the oxygen atom in the Xantphos ligand [30]. When using α-olefin as a substrate, the cobalt atom should be located at the terminal position due to the avoidance of steric repulsion between the bulky Xantphos ligand and an alkyl substitution (similar

Cationic cobalt-catalyzed [1,3]-rearrangement of N-alkoxycarbonyloxyanilines

• Itaru Nakamura,
• Mao Owada,
• Takeru Jo and
• Masahiro Terada

Beilstein J. Org. Chem. 2018, 14, 1972–1979, doi:10.3762/bjoc.14.172

• , Aoba-ku, Sendai 980-8578 Japan 10.3762/bjoc.14.172 Abstract A cationic cobalt catalyst efficiently promoted the reaction of N-alkoxycarbonyloxyanilines at 30 °C, affording the corresponding ortho-aminophenols in good to high yields. As reported previously, our mechanistic studies including oxygen-18

• labelling experiments indicate that the rearrangement of the alkoxycarbonyloxy group proceeds in [1,3]-manner. In this article, we discuss the overall picture of the cobalt-catalysed [1,3]-rearrangement reaction including details of the reaction conditions and substrate scope. Keywords: anilines; cobalt

• reaction conditions with high functional group tolerance. Based on this concept, we disclosed that cationic cobalt catalysts efficiently promote the reaction of O-alkoxylcarbonyl-N-arylhydroxylamines 1 at 30 °C, affording the corresponding 2-aminophenol derivatives 2 in good to high yields [13]. Our

Graphitic carbon nitride prepared from urea as a photocatalyst for visible-light carbon dioxide reduction with the aid of a mononuclear ruthenium(II) complex

• Kazuhiko Maeda,
• Daehyeon An,
• Ryo Kuriki,
• Daling Lu and
• Osamu Ishitani

Beilstein J. Org. Chem. 2018, 14, 1806–1812, doi:10.3762/bjoc.14.153

• using cobalt-based metal complexes as reduction cocatalysts [17][18][19][20]. In these systems, structural properties of g-C3N4 such as specific surface area and porosity have a strong impact on activity, because they strongly affect the efficiency of electron/hole utilization to the surface chemical

β-Hydroxy sulfides and their syntheses

• Mokgethwa B. Marakalala,
• Edwin M. Mmutlane and
• Henok H. Kinfe

Beilstein J. Org. Chem. 2018, 14, 1668–1692, doi:10.3762/bjoc.14.143

• , alcohols, thiols, and azides as the nucleophiles [53]. The Eu3+ and Tb3+ versions were prepared by metal exchange in methanol, between the cobalt complex 67 and the triflate salts of the rare earths, giving the desired complexes CP1 and CP2 in 83% and 86% yield, respectively. The solvent free thiolysis of

Thiocarbonyl-enabled ferrocene C–H nitrogenation by cobalt(III) catalysis: thermal and mechanochemical

• Santhivardhana Reddy Yetra,
• Zhigao Shen,
• Hui Wang and
• Lutz Ackermann

Beilstein J. Org. Chem. 2018, 14, 1546–1553, doi:10.3762/bjoc.14.131

• by weakly-coordinating thiocarbonyl-assisted cobalt catalysis. Thus, carboxylates enabled ferrocene C–H nitrogenations with dioxazolones, featuring ample substrate scope and robust functional group tolerance. Mechanistic studies provided strong support for a facile organometallic C–H activation

• manifold. Keywords: amidation; C–H activation; cobalt; ferrocene; mechanochemistry; Introduction C–H activation has surfaced as a transformative tool in molecular sciences [1][2][3][4][5][6][7][8][9]. While major advances have been accomplished with precious 4d transition metals, recent focus has shifted

• towards more sustainable base metals [10][11][12][13][14][15][16][17], with considerable progress by earth-abundant cobalt catalysts [18][19][20][21][22]. In this context, well-defined cyclopentadienyl-derived cobalt(III) complexes have proven instrumental for enabling a wealth of C–H transformations [23

Cobalt-catalyzed C–H cyanations: Insights into the reaction mechanism and the role of London dispersion

• Eric Detmar,
• Valentin Müller,
• Daniel Zell,
• Lutz Ackermann and
• Martin Breugst

Beilstein J. Org. Chem. 2018, 14, 1537–1545, doi:10.3762/bjoc.14.130

• Abstract Carboxylate-assisted cobalt(III)-catalyzed C–H cyanations are highly efficient processes for the synthesis of (hetero)aromatic nitriles. We have now analyzed the cyanation of differently substituted 2-phenylpyridines in detail computationally by density functional theory and also experimentally

• -phenylpyridine furthermore highlight that London dispersion is an important factor that enables this challenging C–H transformation. Nonbonding interactions between the Cp* ligand and aromatic and C–H-rich fragments of other ligands at the cobalt center significantly contribute to a stabilization of cobalt

• , the strategic application of London dispersion in catalysis is still very difficult to achieve and, as a consequence, detailed insights in how dispersion influences organic reactions continue to be in high demand. Therefore, we have computationally analyzed the recently developed cobalt-catalyzed C–H

Cobalt–metalloid alloys for electrochemical oxidation of 5-hydroxymethylfurfural as an alternative anode reaction in lieu of oxygen evolution during water splitting

• Jonas Weidner,
• Stefan Barwe,
• Kirill Sliozberg,
• Stefan Piontek,
• Justus Masa,
• Ulf-Peter Apfel and
• Wolfgang Schuhmann

Beilstein J. Org. Chem. 2018, 14, 1436–1445, doi:10.3762/bjoc.14.121

• valuable product for the chemical industry with potential large scale use. Various cobalt–metalloid alloys (CoX; X = B, Si, P, Te, As) were investigated as potential catalysts for HMF oxidation. In this series, CoB required 180 mV less overpotential to reach a current density of 55 mA cm−2 relative to OER

• [4]. The elaborate separation of TEMPO from FDCA appeared to be an additional disadvantage [24]. Recently, Sun and co-workers reported the electrochemical oxidation of HMF using various non-precious cobalt and nickel based bifunctional HER/OER water splitting electrocatalysts, namely CoP on copper

• foam, Ni2P and Ni3S2 on nickel foam, in a one compartment batch type electrochemical reactor [5][28][29]. We recently reported on the synthesis and application of alloys of cobalt with boron and phosphorus as exceptionally active bifunctional HER/OER catalysts for water splitting. Inspired by these

Three-component coupling of aryl iodides, allenes, and aldehydes catalyzed by a Co/Cr-hybrid catalyst

• Kimihiro Komeyama,
• Shunsuke Sakiyama,
• Kento Iwashita,
• Itaru Osaka and
• Ken Takaki

Beilstein J. Org. Chem. 2018, 14, 1413–1420, doi:10.3762/bjoc.14.118

• Kimihiro Komeyama Shunsuke Sakiyama Kento Iwashita Itaru Osaka Ken Takaki Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, 1-4-1 Higashi-Hiroshima City 739-8527, Japan 10.3762/bjoc.14.118 Abstract The cobalt/chromium-catalyzed three-component coupling of aryl

• iodides, allenes, and aldehydes has been developed to afford multi-substituted homoallylic alcohols in a diastereoselective manner. Control experiments for understanding the reaction mechanism reveal that the cobalt catalyst is involved in the oxidative addition and carbometalation steps in the reaction

• , whereas the chromium salt generates highly nucleophilic allylchromium intermediates from allylcobalt species, without the loss of stereochemical information, to allow the addition to aldehydes. Keywords: chromium; cobalt; diastereoselective; homoallyl alcohols; hybrid catalyst; three-component coupling

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

An overview of recent advances in duplex DNA recognition by small molecules

• Sayantan Bhaduri,
• Nihar Ranjan and
• Dev P. Arya

Beilstein J. Org. Chem. 2018, 14, 1051–1086, doi:10.3762/bjoc.14.93

Cobalt-catalyzed directed C–H alkenylation of pivalophenone N–H imine with alkenyl phosphates

• Wengang Xu and
• Naohiko Yoshikai

Beilstein J. Org. Chem. 2018, 14, 709–715, doi:10.3762/bjoc.14.60

• Wengang Xu Naohiko Yoshikai Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore 10.3762/bjoc.14.60 Abstract A cobalt–N-heterocyclic carbene (NHC) catalyst efficiently promotes an ortho C–H

• alkenylation reaction of pivalophenone N–H imine with an alkenyl phosphate. The reaction tolerates various substituted pivalophenone N–H imines as well as cyclic and acyclic alkenyl phosphates. Keywords: alkenylation; C–C bond formation; C–H activation; cobalt; imine; Introduction Transition-metal-catalyzed

• ) from ketones [13][14][15][16][17]. Over the last several years, we and others have developed a series of directed arene C–H functionalization reactions with organic electrophiles under low-valent cobalt catalysis [18][19][20][21]. In particular, our group and the Ackermann group have independently

Photocatalytic formation of carbon–sulfur bonds

• Alexander Wimmer and
• Burkhard König

Beilstein J. Org. Chem. 2018, 14, 54–83, doi:10.3762/bjoc.14.4

• generate a carbon-centred radical intermediate. The cobalt-catalyst is involved in two ways: oxidation and deprotonation of the radical species yielding the desired product and oxidation of the Eosin Y radical anion to close the photocatalytic cycle. The H2 evolution was not quantitative, which was

Pd(OAc)₂/Ph₃P-catalyzed dimerization of isoprene and synthesis of monoterpenic heterocycles

• Dominik Kellner,
• Maximilian Weger,
• Andrea Gini and
• Olga García Mancheño

Beilstein J. Org. Chem. 2017, 13, 1807–1815, doi:10.3762/bjoc.13.175

• , titanium-, zirconium-, iron-, cobalt-, vanadium- or aluminum-based Ziegler-type catalysts lead mostly to the linear tail-to-head 2-TH dimer 2,6-dimethyl-1,3,6-octatriene (alloocimene) [27], and the use of nickel catalysts allows the preparation of the tail-to-tail dimer 2-TT (2,7-dimethyl-1,3,7-octatriene

Ni nanoparticles on RGO as reusable heterogeneous catalyst: effect of Ni particle size and intermediate composite structures in C–S cross-coupling reaction

• Debasish Sengupta,
• Koushik Bhowmik,
• Goutam De and
• Basudeb Basu

Beilstein J. Org. Chem. 2017, 13, 1796–1806, doi:10.3762/bjoc.13.174

• first palladium-catalyzed arylation of thiols was reported by Migita and co-workers in 1980 [5], and soon after Cristau and co-workers developed a nickel-catalyzed route for C–S cross-coupling reactions [6]. Other metals such as copper [7], cobalt [8], iron [9], rhodium [10], manganese [11], indium [12

Oxidative dehydrogenation of C–C and C–N bonds: A convenient approach to access diverse (dihydro)heteroaromatic compounds

• Santanu Hati,
• Ulrike Holzgrabe and
• Subhabrata Sen

Beilstein J. Org. Chem. 2017, 13, 1670–1692, doi:10.3762/bjoc.13.162

• reaction was facilitated at room temperature by N-hydroxyphthalimide (NHPI) and cobalt acetate (Co(OAc)2) as catalysts in acetonitrile (Scheme 20). The reaction followed a free radical mechanism as exemplified by the oxidative dehydrogenation of DHPs. The initial step involved the formation of the

• (Scheme 41). The catalytic system comprised of an octahedral [Ru(phd)3]2+ catalyst along with cobalt-N,N´-bis(salicylidene)-1,2-phenylenediamine [Co(Salophen)] as a redox co-catalyst. The reaction occurs aerobically under mild conditions (Scheme 41) [100]. Our final example demonstrated the utility of

• , phd = 1,10-phenanthroline-5,6-dione. Oxidative dehydrogenation with Flavin mimics. o-Quinone based bioinspired catalysts for the synthesis of dihydroisoquinolines. Cobalt-catalyzed aerobic dehydrogenation of Hantzch 1,4-DHPs and pyrazolines. Mechanism of cobalt-catalyzed aerobic dehydrogenation of

Unpredictable cycloisomerization of 1,11-dien-6-ynes by a common cobalt catalyst

• Abdusalom A. Suleymanov,
• Dmitry V. Vasilyev,
• Valentin V. Novikov,
• Yulia V. Nelyubina and
• Dmitry S. Perekalin

Beilstein J. Org. Chem. 2017, 13, 639–643, doi:10.3762/bjoc.13.62

• cycloisomerization in the presence of the cobalt catalytic system CoBr2/phosphine ligand/Zn/ZnI2 giving cyclohexene, diene or cyclopropane structures depending on the type of the phosphine ligand. This unpredictable behaviour suggests that, although the availability of the cobalt catalytic system is appealing, the

• development of well-defined catalysts is desirable for further progress. Keywords: catalysis; cobalt; cyclization; enynes; ligands; Introduction Metal-catalyzed reactions of enynes represent an atom- and step-economical route to complex organic molecules with a broad range of functionalities [1][2][3][4

• polycycles [8][11][12][13] (Scheme 1). However, all these transformations require expensive noble metal catalysts with rather sophisticated ligands. Therefore, the development of a cheap catalyst for such reactions is highly desirable. Over the last decade the application of the cobalt catalytic system CoBr2

Effect of the ortho-hydroxy group of salicylaldehyde in the A³ coupling reaction: A metal-catalyst-free synthesis of propargylamine

• Sujit Ghosh,
• Kinkar Biswas,
• Suchandra Bhattacharya,
• Pranab Ghosh and
• Basudeb Basu

Beilstein J. Org. Chem. 2017, 13, 552–557, doi:10.3762/bjoc.13.53

• ], mercury [26], cobalt [27], iridium [28], ruthenium [29], indium [30] etc. Other methods towards the synthesis of propargylamine include: alkynylation of imine [31][32][33], enamine [34], and Csp³–H bonds adjacent to N-atoms [35][36]. In the A3 coupling, the role of the metal catalyst is believed to