Synthesis of Substituted 2,2′‐Bipyridines and 2,2′:6′,2′′‐Terpyridines by Cobalt‐Catalyzed Cycloaddition Reactions of Nitriles and α,ω‐Diynes with Exclusive Regioselectivity

A variety of substituted 2,2′‐bipyridines were synthesized by a 1,2‐bis(diphenylphosphino)ethane (dppe)/cobalt chloride hexahydrate (CoCl₂⋅6 H₂O)/zinc‐catalyzed [2+2+2] cycloaddition reaction of diynes and nitriles, with all reactions exhibiting exclusive regioselectivity. Thus, symmetrical and unsymmetrical 1,6‐diynes and 2‐cyanopyridine reacted in the presence of 5 mol % of dppe, 5 mol % of CoCl₂⋅6 H₂O and 10 mol % of zinc powder to provide the corresponding 2,2′‐bipyridines. Under identical reaction conditions, 1‐(2‐pyridyl)‐1,6‐diynes and nitriles reacted smoothly with exclusive regioselectivity to produce 2,2′‐bipyridines in good yield. 2,2′‐Bipyridines were also obtained by the double [2+2+2] cycloaddition reaction of 1,6,8,13‐tetraynes with nitriles. Similarly, 2,2′:6′,2′′‐terpyridines were synthesized from 1‐(2‐pyridyl)‐1,6‐diyne and 2‐cyanopyridine. The regiochemistry observed can be explained by considering the electronic nature of cobaltacyclopentadiene intermediates and nitriles. A survey of the exclusive regiochemical trend gives reasonable credence to the synthetic potential of the present method.     

Development of Nickel‐on‐Charcoal as a ‘‘Dirt‐Cheap’’ Heterogeneous Catalyst: A Personal Account

A personal account tracing the origins and continuing evolution of nickel‐on‐charcoal (Ni/C) as a practical, alternative, group 10 metal catalyst is presented. Discussed are applications to several ‘‘name reactions’’ which lead to both carbon−carbon and carbon−nitrogen bond constructions utilizing inexpensive aryl chlorides as substrates. Reductions of chloroarenes are also catalyzed by Ni/C, a process which may be worthy of consideration in terms of environmental cleanup of PCBs and dioxins. Collaborative efforts are also mentioned aimed at probing the surface structure of Ni/C, with the goal of enhancing catalyst activity. Future directions for development of heterogeneous nickel catalysts are proposed. 1 Introduction: Nickel‐on‐Charcoal? Never Heard of It… 2 Mixing a Ni(II) Salt with Charcoal: Getting It to ‘Stick’ and Reduction to Ni(0) 3 First Results: Negishi‐Like Couplings with Functionalized Zinc Reagents 4 Is Ni/C Compatible with Grignard Reagents? Kumada‐Like Couplings 5 Suzuki Couplings with Aryl Chlorides: Ni/C Takes the Challenge 6 Aminations of Aryl Chlorides: and the ‘Magic’ Phosphine Ligand is… 7 Reductive Dechlorinations of Aryl Chlorides: Searching for a Mild Source of Hydride 8 What Does “Ni/C” Really Look Like? Surface Science to the Rescue 9 Summary… and a Look Ahead     

Development of Nickel‐on‐Charcoal as a ‘‘Dirt‐Cheap’’ Heterogeneous Catalyst: A Personal Account

In the review by B. H. Lipschutz in Issue 4, 2001, pp. 313–326 Equation 3 on page 317 was inadvertently replaced with Equation 5. The correct Equation 3 is given here.     

Fluorescent chemosensor based on the conjugated polymer incorporating 2,2′‐bipyridyl moiety for transition metal ions

A fluorescent conjugated polymer was synthesized by the polymerization of 1,4‐dibromo‐2,3‐bisbutoxynaphthalene ( M‐2 ) with 5,5′‐divinyl‐2,2′‐bipyridine ( M‐3 ) via Heck reaction. The conjugated polymer shows strong blue–green fluorescence because of the extended π‐electronic structure between the repeating unit 2,3‐bisbutoxynaphthyl group and the conjugated linker 2,2′‐bipyridyl (bpy = 2,2′‐bipyridine) moiety via vinylene bridge. The responsive properties of the conjugated polymer on transition metal ions were investigated by fluorescent and UV–vis spectra. The results show that Cu²⁺ and Ni²⁺ can form nonradiative metal‐to‐ligand charge‐transfer complexes with the polymer, whereas, Zn²⁺ and Cd²⁺ do not produce the pronounced differences from the polymer fluorescence and UV–vis spectra. The fluorescent quenching can probably be attributed to the intramolecular photoinduced electron transfer (PET) or photoinduced charge transfer (PCT). The results can also suggest that 2,2′‐bipyridyl moiety in the main chain backbone of the conjugated polymer can act as the recognition site of a special fluorescent chemosensor for sensitive detection of transition metal ions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Ligand‐Free Nickel‐Catalysed 1,4‐Addition of Arylboronic Acids to α,β‐Unsaturated Carbonyl Compounds

A simple and efficient ligand‐free nickel‐based catalytic system has been developed for the 1,4‐addition of arylboronic acids to α,β‐unsaturated carbonyl compounds. With catalyst loadings of 1–2 mol%, a series of 1,4‐adducts from chalcones and cinnamates was obtained in moderate to excellent yields within 5–30 min under a nitrogen atmosphere and microwave irradiation. The 1,4‐addition of arylboronic acids to acrylates is less efficient.

     

Calixarene‐Derived Mono‐Iminophosphoranes: Highly Efficient Ligands for Palladium‐ and Nickel‐Catalysed Cross‐Coupling

The first mono‐iminophosphoranes based on a calix[4]arene skeleton have been synthesised and tested in the arylation of aryl bromides and aryl chlorides. Combining these ligands with [Pd(OAc)₂] or [Ni(cod)₂] resulted in highly active Suzuki–Miyaura and Kumada–Tamao–Corriu cross‐coupling catalysts, respectively. TOFs up to ca. 4×10⁵ mol(ArBr)⋅mol(M)⁻¹⋅h⁻¹ were obtained in each case. The remarkable activities observed probably arise from the ligands’ ability to form complexes with cavity‐entrapped “MArX” moieties (endo‐complexes), their highly crowded metal environment favouring formation of mono‐ligated intermediates over that of less reactive bis‐ligated ones. Possible supramolecular interactions within the cavity involving the receptor wall and the aromatic substrate may also significantly influence the reaction rates, notably by increasing the proportion of endo‐complexes.     

Aerobic oxidative radical coupling catalyzed by TEMPO for the preparation of 2,2′‐dibenzothiazole disulfide

BACKGROUND: 2,2′‐disbenzothiazole disulfide is widely used as a vulcanization accelerator in rubber production and as an intermediate in the drug industry. Its current industrial process, the oxidation of 2‐mercaptobenzothiazole by sodium nitrite in acidic solution, produces large quantities of liquid waste water. A novel and green synthetic method was developed, which used dioxygen as the oxidant and 2,2,6,6‐tetramethylpiperidyl‐1‐oxyl (TEMPO) as the catalyst without any metallic compounds. RESULTS: The conditions, including temperature, solvents, amount of catalyst, dioxygen pressure and time, were optimized. Thus 94% yield of 2,2′‐disbenzothiazole disulfide was obtained at 60 °C in acetonitrile under 0.2 MPa oxygen pressure for 3 h. Theoretical calculations and UV spectra showed that hydrogen‐transfer reaction between 2‐mercaptobenzothiazole and TEMPO was the key step, and 2,2′‐disbenzothiazole disulfide was generated by the coupling of the formed thiyl radical of 2‐mercaptobenzothiazole. CONCLUSION: 2,2′‐disbenzothiazole disulfide was prepared efficiently by aerobic oxidative coupling of 2‐mercaptobenzothiazole with TEMPO as the catalyst. This ‘environmentally friendly’ approach with easy handling, mild reaction conditions and simple separation represents a viable means of producing 2,2′‐disbenzothiazole disulfide. Copyright © 2011 Society of Chemical Industry     

Molecular simulation of the glass transition and proton conductivity of 2,2′‐benzidinedisulfonic acid and 4,4′‐diaminodiphenylether‐2,2′‐disulfonic acid‐based copolyimides as polyelectrolytes for fuel cell applications

The glass transition temperatures (T_gs) and proton conductivities of polyimides synthesized from naphthalene‐1,4,5,8‐tetracarboxylic dianhydride (NTDA), 2,2′‐benzidinedisulfonic acid (BDSA), 4,4′‐diaminodiphenylether‐2,2′‐disulfonic acid (ODADS), and non‐sulfonated diamine monomers have been predicted using molecular dynamics simulations. The specific volumes for two dry and four hydrated NTDA‐based polyimides were plotted versus temperatures above and below T_gs to obtain the glass transition temperatures. The simulation results suggest that the ODADS‐based polyimide membranes exhibit lower T_gs and thus better mechanical properties than the BDSA‐based polyimides, which may be attributed to the high mobility of backbones of ODADS as supported by the vectorial autocorrelation function (VACF) results of this study. In addition, comparison of the simulated T_gs for the dry and hydrated ODADS‐based polyimides has shown that water content in polyimides can affect their T_gs. The proton conductivities of a representative polyimide in both dry and hydrated conditions have been obtained from molecular dynamics simulations of the proton and hydronium ion diffusion. The simulated conductivity for the hydrated NTDA‐ODADS/BAPB cell is in reasonable agreement with the experimental value obtained from the AC impedance method. The relationship between the chemical composition, chain flexibility, and the glass transition and proton conduction of these NTDA‐based polyimides was explored on the basis of VACF and pair correlation function analysis. Copyright © 2006 Society of Chemical Industry     

New Pathway to C2‐Symmetric Atropoisomeric Bipyridine N,N′‐Dioxides and Solvent Effect in Enantioselective Allylation of Aldehydes

The [2+2+2] cyclotrimerization of 1,7,9,15‐hexadecatetrayne with nitriles catalyzed by dicarbonylcyclopentadienylcobalt(I) opened a new pathway for the synthesis of C₂‐symmetrical bis(tetrahydroisoquinolines) that were used as starting material for the preparation of axially chiral bipyridine N,N′‐dioxides. The N,N′‐dioxides (1 mol%) were found to be highly catalytically active and enantioselective (up to 83% ee) for the asymmetric allylation of aldehydes with allyl(trichloro)silane in various solvents. In addition, a dramatic solvent effect was observed where the use of different solvents induced opposite chiralities of the product with the same enantiomer of the catalyst, e.g., 65% ee (S) in acetonitrile (MeCN) vs. 82% ee (R) in chlorobenzene.     

A Convenient Synthesis of 2,2′,6,6′‐Tetramethoxy‐ 4,4′‐bis(dicyclohexylphosphino)‐3,3′‐bipyridine (Cy‐P‐Phos): Application in Rh‐Catalyzed Asymmetric Hydrogenation of α‐(Acylamino)acrylates

The first example of the synthesis of an axially chiral bis(aryldicyclohexylphosphine) dioxide via catalytic hydrogenation of the optically resolved parent bis(aryldiphenylphosphine) dioxide was reported. The procedure for the synthesis of Cy‐P‐Phos ( 4d ) has thus successfully avoided the need for an otherwise lengthy synthetic route owing to the π‐excessive nature of one of the aryl groups in the latter. The use of Cy‐P‐Phos in the Rh(I)‐catalyzed asymmetric hydrogenation of the derivatives of methyl (Z)‐2‐acetamidocinnamate gave significantly higher rates of reaction as compared to the use of the previously reported optimal ligand Xyl‐P‐Phos ( 4c ) whilst the level of enantioselectivity was essentially maintained.     

Synthesis of 5,5′‐Diformyl‐2,2′‐difuran from 2‐Furfural by Photochemical Aryl Coupling

The synthesis of 5,5′‐diformyl‐2,2′‐difuran (IUPAC name: [2,2′‐bifuryl]‐5,5′‐dicarbaldehyde) in good yields by the intermolecular coupling of 2‐furfural and 5‐bromo‐2‐furfural has been achieved. Optimum yields were obtained when mixtures of the substrates in acetonitrile were treated with polyvinylpyridine powder (Reillex 402), and irradiated with UV light through a quartz filter. Low yields of coupling product were obtained in the absence of this base or if hydrocarbon solvents were used. A mechanistic pathway involving a transient exciplex intermediate has been proposed.     

Synthesis and properties of organosoluble polyimides derived from 2,2′‐dibromo‐ and 2,2′,6,6′‐tetrabromo‐4,4′‐oxydianilines

Two new aromatic diamines, 2,2′‐dibromo‐4,4′‐oxydianiline (DB‐ODA 4 ) and 2,2′,6,6′‐tetrabromo‐4,4′‐oxydianiline (TB‐ODA 5 ), have been synthesized by oxidation, bromination, and reduction of 4,4′‐oxydianiline (4,4′‐ODA). Novel polyimides 6a–f and 7a–f were prepared by reacting DB‐ODA ( 4 ) and TB‐ODA ( 5 ) with several dianhydrides by one‐step method, respectively. The inherent viscosities of these polyimides ranged from 0.31 to 0.99 dL/g (0.5 g/dL, in NMP at 30°C). These polyimides showed enhanced solubilities compared to those derived from 4,4′‐oxydianiline and corresponding dianhydrides. Especially, polyimides 7a , derived from rigid PMDA and TB‐ODA ( 5 ) can also be soluble in THF, DMF, DMAc, DMSO, and NMP. These polyimides also exhibited good thermal stability. Their glass transition temperatures measured by thermal mechanical analysis (TMA) ranged from 251 to 328°C. When the same dianhydrides were used, polyimides 7 containing four bromide substituents had higher glass transition temperatures than polyimides 6 containing two bromide substituents. The effects of incorporating more polarizable bromides on the refractive indices of polyimides were also investigated. The average refractive indices (n_av) measured at 633 nm were from 1.6088 to 1.7072, and the in‐plane/out‐of‐plane birefringences (Δn) were from 0.0098 to 0.0445. It was found that the refractive indices are slightly higher when polyimides contain more bromides. However, this effect is not very obvious. It might be due to loose chain packing resulted from bromide substituents at the 2,2′ and 2,2′,6,6′ positions of the oxydiphenylene moieties. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Facile Palladium‐Catalyzed Synthesis of 3‐Arylpyrazolo[1,5‐a]pyrimidines

An efficient palladium‐catalyzed synthesis of 3‐arylpyrazolo[1,5‐a]pyrimidines has been investigated. The key step in the synthesis is a Suzuki biaryl coupling of 3‐bromo‐2,5‐dimethyl‐7‐aminopyrazolo[1,5‐a]pyrimidines with arylboronic acids to provide 3‐arylpyrazolo[1,5‐a]pyrimidines in moderate to good yield. The synthetic utility of this methodology has been demonstrated by a concise and convergent synthesis of R121920, a potent CRHR₁ antagonist recently undergoing clinical evaluations.     

Enzymatic Redox Cascade for One‐Pot Synthesis of Uridine 5′‐Diphosphate Xylose from Uridine 5′‐Diphosphate Glucose

Synthetic ways towards uridine 5′‐diphosphate (UDP)‐xylose are scarce and not well established, although this compound plays an important role in the glycobiology of various organisms and cell types. We show here how UDP‐glucose 6‐dehydrogenase (hUGDH) and UDP‐xylose synthase 1 (hUXS) from Homo sapiens can be used for the efficient production of pure UDP‐α‐xylose from UDP‐glucose. In a mimic of the natural biosynthetic route, UDP‐glucose is converted to UDP‐glucuronic acid by hUGDH, followed by subsequent formation of UDP‐xylose by hUXS. The nicotinamide adenine dinucleotide (NAD⁺) required in the hUGDH reaction is continuously regenerated in a three‐step chemo‐enzymatic cascade. In the first step, reduced NAD⁺ (NADH) is recycled by xylose reductase from Candida tenuis via reduction of 9,10‐phenanthrenequinone (PQ). Radical chemical re‐oxidation of this mediator in the second step reduces molecular oxygen to hydrogen peroxide (H₂O₂) that is cleaved by bovine liver catalase in the last step. A comprehensive analysis of the coupled chemo‐enzymatic reactions revealed pronounced inhibition of hUGDH by NADH and UDP‐xylose as well as an adequate oxygen supply for PQ re‐oxidation as major bottlenecks of effective performance of the overall multi‐step reaction system. Net oxidation of UDP‐glucose to UDP‐xylose by hydrogen peroxide (H₂O₂) could thus be achieved when using an in situ oxygen supply through periodic external feed of H₂O₂ during the reaction. Engineering of the interrelated reaction parameters finally enabled production of 19.5 mM (10.5 g L ⁻¹) UDP‐α‐xylose. After two‐step chromatographic purification the compound was obtained in high purity (>98%) and good overall yield (46%). The results provide a strong case for application of multi‐step redox cascades in the synthesis of nucleotide sugar products.

     

Synthesis and characterization of novel aromatic poly(amide‐imide)s derived from 2,2′‐bis(4‐trimellitimidophenoxy)biphenyl or 2,2′‐bis(4‐trimellitimidophenoxy)‐1,1′‐binaphthyl and various aromatic diamines

New aromatic diimide‐dicarboxylic acids having kinked and cranked structures, 2,2′‐bis(4‐trimellitimidophenoxy)biphenyl (2a) and 2,2′‐bis(4‐trimellitimidophenoxy)‐1,1′‐binaphthyl (2b), were synthesized by the reaction of trimellitic anhydride with 2,2′‐bis(4‐aminophenoxy)biphenyl (1a) and 2,2′‐bis(4‐aminophenoxy)‐1,1′‐binaphthyl (1b), respectively. Compounds 2a and 2b were characterized by FT‐IR and NMR spectroscopy and elemental analyses. Then, a series of novel aromatic poly(amide‐imide)s were prepared by the phosphorylation polycondensation of the synthesized monomers with various aromatic diamines. Owing to structural similarity, and a comparison of the characterization data, a model compound was synthesized by the reaction of 2b with aniline. The resulting polymers with inherent viscosities of 0.58–0.97 dl g^?1 were obtained in high yield. The polymers were fully characterized by FT‐IR and NMR spectroscopy. The ultraviolet λ_max values of the poly(amide‐imide)s were also determined. The polymers were readily soluble in polar aprotic solvents. They exhibited excellent thermal stabilities and had 10% weight loss at temperatures above 500 °C under a nitrogen atmosphere. Copyright © 2003 Society of Chemical Industry     

Electropolymerization of hydrogen bond supramolecular associations between terthiophene‐3‐acetic acid and 4,4′‐bipyridine

Supramolecular assemblies based on 4,4′‐bipyridine as hydrogen acceptor and a terthiophene carboxylic acid (3‐TTAA) as hydrogen donor were synthesized and characterized by Fourier transform IR spectroscopy and DSC. Their electropolymerization was successful in methylene chloride or acetonitrile. The concept of using such supramolecular assemblies in electropolymerization opens the way to the facile synthesis of new π‐conjugated polymers. © 2017 Society of Chemical Industry     

Synthesis and characterization of novel polyaspartimides derived from 2,2′‐dimethyl‐4,4′‐bis(4‐maleimidophenoxy)biphenyl and various diamines

A novel bismaleimide, 2,2′‐dimethyl‐4,4′‐bis(4‐maleimidophenoxy)biphenyl, containing noncoplanar 2,2′‐dimethylbiphenylene and flexible ether units in the polymer backbone was synthesized from 2,2′‐dimethyl‐4,4′‐bis(4‐aminophenoxy)biphenyl with maleic anhydride. The bismaleimide was reacted with 11 diamines using m‐cresol as a solvent and glacial acetic acid as a catalyst to produce novel polyaspartimides. Polymers were identified by elemental analysis and infrared spectroscopy, and characterized by solubility test, X‐ray diffraction, and thermal analysis (differential scanning calorimetry and thermogravimetric analysis). The inherent viscosities of the polymers varied from 0.22 to 0.48 dL g⁻¹ in concentration of 1.0 g dL⁻¹ of N,N‐dimethylformamide. All polymers are soluble in N‐methyl‐2‐pyrrolidone, N,N‐dimethylacetamide, N,N‐dimethylformamide, dimethylsulfoxide, pyridine, m‐cresol, and tetrahydrofuran. The polymers, except PASI‐4, had moderate glass transition temperature in the range of 188°–226°C and good thermo‐oxidative stability, losing 10% mass in the range of 375°–426°C in air and 357°–415°C in nitrogen. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 279–286, 1999     

Water Solvent Method for Esterification and Amide Formation between Acid Chlorides and Alcohols Promoted by Combined Catalytic Amines: Synergy between N‐Methylimidazole and N,N,N′,N′‐Tetramethylethylenediamine (TMEDA)

An efficient method for esterification between acid chlorides and alcohols in water as solvent has been developed by combining the catalytic amines, N‐methylimidazole and N,N,N′,N′‐tetramethylethylenediamine (TMEDA). The present Schotten–Baumann‐type reaction was performed by maintaining the pH at around 11.5 using a pH controller to prevent the decomposition of acid chlorides and/or esters and to facilitate the condensation. The choice of catalysts (0.1 equiv.) was crucial: the combined use of N‐methylimidazole and TMEDA exhibited a dramatic synergistic effect. The catalytic amines have two different roles: (i) N‐methylimidazole forms highly reactive ammonium intermediates with acid chlorides and (ii) TMEDA acts as an effective HCl binder. The production of these intermediates was rationally supported by a careful ¹H NMR monitoring study. Related amide formation was also achieved between acid chlorides and primary or secondary amines, including less nucleophilic or water‐soluble amines such as 2‐(or 4‐)chloroaniline, the Weinreb N‐methoxyamine, and 2,2‐dimethoxyethanamine.     

Synthesis and characterization of new thermally stable poly(ester‐imide)s derived from 2,2′‐bis(4‐trimellitimidophenoxy)biphenyl and 2,2′‐bis(4‐trimellitimidophenoxy)‐1,1′‐binaphthyl and various aromatic dihydroxy compounds

A series of new alternating aromatic poly(ester‐imide)s were prepared by the polycondensation of the preformed imide ring‐containing diacids, 2,2′‐bis(4‐trimellitimidophenoxy)biphenyl (2a) and 2,2′‐bis(4‐trimellitimidophenoxy)‐1,1′‐binaphthyl (2b) with various aromatic dihydroxy compounds in the presence of pyridine and lithium chloride. A model compound (3) was also prepared by the reaction of 2b with phenol, its synthesis permitting an optimization of polymerization conditions. Poly(ester‐imides) were fully characterized by FTIR, UV‐vis and NMR spectroscopy. Both biphenylene‐ and binaphthylene‐based poly(ester‐imide)s exhibited excellent solubility in common organic solvents such as tetrahydrofuran, m‐cresol, pyridine and dichloromethane. However, binaphthylene‐based poly(ester‐imide)s were more soluble than those of biphenylene‐based polymers in highly polar organic solvents, including N‐methyl‐2‐pyrrolidone, N,N‐dimethylacetamide, N,N‐dimethylformamide and dimethyl sulfoxide. From differential scanning calorimetry thermograms, the polymers showed glass‐transition temperatures between 261 and 315 °C. Thermal behaviour of the polymers obtained was characterized by thermogravimetric analysis, and the 10 % weight loss temperatures of the poly(ester‐imide)s was in the range 449–491 °C in nitrogen. Furthermore, crystallinity of the polymers was estimated by means of wide‐angle X‐ray diffraction. The resultant poly(ester‐imide)s exhibited nearly an amorphous nature, except poly(ester‐imide)s derived from hydroquinone and 4,4′‐dihydroxybiphenyl. In general, polymers containing binaphthyl units showed higher thermal stability but lower crystallinity than polymers containing biphenyl units. Copyright © 2005 Society of Chemical Industry