Electrogenerated Nickel Catalyst for C-N Cross-Coupling.

Arylamines represent a class of compounds widely found in natural products and pharmaceuticals. Among methodologies devoted to their synthesis, nickel-catalyzed amination of aryl halides constitutes one of the most employed conventional strategies. However, C-N cross-couplings often involve elaborated nickel complexes, which are expensive and/or air and moisture sensitive. To circumvent this issue, we herein report an electrochemical method based on a sacrificial anode process to in situ generate a catalytic amount of nickel salts allowing amination of aryl halides. The approach, simple to set up, proceeds under mild reaction conditions and enables access to a large panel of arylamines.

Synthesis of α-Chloroarylacetic Acid via Electrochemical Carboxylation of α,α-Dichloroarylmethane Derivatives.

The electrocarboxylation of α,α-dichloroarylmethane derivatives in the presence of CO2 was achieved, providing several α-chloroarylacetic acid derivatives with modest yields but high selectivity (chlorinated vs. non-chlorinated or dicarboxylic acid products). The obtained products were then involved in several chemical transformations, underlining their potential as versatile intermediates in synthetic chemistry. A mechanism was also proposed based upon a control experiment and cyclic voltammetry (CV) study.

Controlled decomposition of SF6 by electrochemical reduction.

The electroreduction of SF6 is shown at ambient temperature in acetonitrile using an array of platinum microelectrodes to improve the electrical detection. Its half reduction potential occurs at -2.17 V vs Fc+/Fc. The exact number of electrons for the full consumption of sulfur hexafluoride was determined and this gas further quantitatively transformed into environmentally benign fluoride anion and sulfur by electrochemical reduction.

CoI -Catalyzed Barbier Reactions of Aromatic Halides with Aromatic Aldehydes and Imines.

The reductive Barbier coupling of aromatic halides and electrophiles has been achieved using a CoBr2 /1,10-phenanthroline catalytic system and over stoichiometric amounts of zinc. The reaction displayed a broad scope of substrates, including (hetero)aryl chlorides as pro-nucleophiles and aldehydes or imines as electrophiles, leading to diarylmethanols and diarylmethylamines in moderate to excellent yields, respectively.

Synthesis and biological evaluation of 3-amino-, 3-alkoxy- and 3-aryloxy-6-(hetero)arylpyridazines as potent antitumor agents.

Various 3-amino-, 3-aryloxy- and alkoxy-6-arylpyridazines have been synthesized by an electrochemical reductive cross-coupling between 3-amino-, 3-aryloxy- or 3-alkoxy-6-chloropyridazines and aryl or heteroaryl halides. In vitro antiproliferative activity of these products was evaluated against a representative panel of cancer cell lines (HuH7, CaCo-2, MDA-MB-231, HCT116, PC3, NCI-H727, HaCaT) and oncogenicity prevention of the more efficient derivatives was highlighted on human breast cancer cell line MDA-MB 468-Luc prior establishing their interaction with p44/42 and Akt-dependent signaling pathways.

Co(I)-Catalyzed [3 + 2] Annulation of o-Haloaryl Imines with Alkenes for the Synthesis of Indanamines.

The use of a CoBr2/1,10-phenanthroline catalytic system together with Zn as the reductant was developed to prepare diversely substituted indanamines by a Co(I)-catalyzed [3 + 2] annulation of o-haloaryl imines with electron-deficient alkenes in good yields. The use of Mn as the reductant allowed the elaboration of a three-component version of this reaction. These conditions were also found to be suitable for the activation of various halides and were extended to the preparation of the indenamine and strigolactam scaffolds.

A mild electroassisted synthesis of (hetero)arylphosphonates.

The electrochemically-assisted synthesis of (hetero)arylphosphonates from (hetero)aryl halides and dimethyl phosphite is described. Very mild and simple conditions are employed as the cross-coupling is carried out in galvanostatic mode, in an undivided cell at room temperature, using NiBr2bpy as the easily available pre-catalyst and acetonitrile as the solvent. In addition, both aryl bromides and iodides can be used as well, providing the corresponding (hetero)arylphosphonates in generally good yields. A mechanism involving the in situ generation of a Ni ate complex is proposed.

Cobalt-Catalyzed Reductive Multicomponent Synthesis of ß-Hydroxy- and ß-Aminocarbonyl Compounds under Mild Conditions.

The cobalt-catalyzed multicomponent reaction between sp2 -hybridized organic halides, Michael acceptors, and unsaturated electrophiles has been developed. The reaction proceeds through a formal conjugate addition/aldol or aza-aldol (Mannich) tandem reaction initiated by the in situ metalation of the organic halide by cobalt catalysis. The essentially new reaction conditions that have been developed are very mild and atom-economic. Under these conditions, a broad range of ß-hydroxy- and ß-aminocarbonyl compounds are obtained in good to high yields.

Synthesis of Indolines by a Zn-Mediated Mannich Reaction/Pd-Catalyzed Amination Sequence.

1,2-Disubstituted indolines have been prepared in fair to good yields by a Zn-mediated organometallic Mannich reaction, followed by an intramolecular Pd-catalyzed aromatic amination. The reactions are easy to set up and compatible with a large variety of simple or commercially available reagents. The method was further extended to the preparation of a 1,2,3-trisubstituted indoline.

A multicomponent approach to the synthesis of N-sulfonyl ß(2,3)-amino esters.

The multicomponent synthesis of α,ß-disubstituted N-sulfonyl ß-amino esters is described. It involves a zinc-mediated, cobalt-catalyzed three-component reaction between sulfonylimines, acrylates and organic bromides. A possible mechanism is proposed, emphasizing the intermediate formation of an organocobalt as the initiator of a Mannich-like process.

A four-component reaction involving in situ generated organometallic reagents: straightforward access to ß-amino esters.

Four in one: A straightforward synthesis of ß(2,3)-amino esters is described through a new zinc-mediated, cobalt-catalyzed four-component reaction between organic bromides, alkyl acrylates, amines, and aldehydes (see scheme). Synthesis involves a Mannich-related conjugate addition/aza-aldol domino sequence, allowing the formation of three single bonds in one step. A reaction mechanism, emphasizing the crucial role of zinc salts, is described.

An electrochemical nickel-catalyzed arylation of 3-amino-6-chloropyridazines.

3-Amino-6-aryl- and 3-amino-6-heteroarylpyridazines have been obtained in generally good yield using a nickel-catalyzed electrochemical cross-coupling between 3-amino-6-chloropyridazines and aryl or heteroaryl halides at room temperature. Comparative experiments involving classical palladium-catalyzed reactions, such as Suzuki, Stille, or Negishi cross-couplings, reveal that the electrochemical method can constitute a reliable alternative tool for biaryl formation. A possible reaction mechanism is proposed on the basis of electrochemical analyses.

Synthesis and cytotoxic evaluation of novel paraconic acid analogs.

A novel class of 2,3-tri- and tetrasubstituted γ-butyrolactones analogous to paraconic acids has been synthesized in one step using a straightforward three-component reaction among aryl bromides, dimethyl itaconate and carbonyl compounds. The in vitro cytotoxic activity of representative compounds has been evaluated against a panel of human cancer cell lines (KB, HCT116, MCF7, HL60). While most molecules exhibit a low to moderate background activity on both KB and HL60 cancer cell lines, one compound shows increased antiproliferative activities against both cell lines with IC(50) values in the 10(-7)-10(-6)mol/L range. An extended evaluation indicated that this compound also inhibits PC3, SK-OV3, MCF7R and HL60R cell growth in the same fashion.

An electrochemical synthesis of functionalized arylpyrimidines from 4-amino-6-chloropyrimidines and aryl halides.

A range of novel 4-amino-6-arylpyrimidines has been prepared under mild conditions by an electrochemical reductive cross-coupling between 4-amino-6-chloro-pyrimidines and functionalized aryl halides. The process, which employs a sacrificial iron anode in conjunction with a nickel(II) catalyst, allows the formation of coupling products in moderate to high yields.

Electrochemical synthesis and characterisation of alternating tripyridyl-dipyrrole molecular strands with multiple nitrogen-based donor-acceptor binding sites.

Synthesis of alternating pyridine-pyrrole molecular strands composed of two electron-rich pyrrole units (donors) sandwiched between three pyridinic cores (acceptors) is described. The envisioned strategy was a smooth electrosynthesis process involving ring contraction of corresponding tripyridyl-dipyridazine precursors. 2,6-Bis[6-(pyridazin-3-yl)]pyridine ligands 2a-c bearing pyridine residues at the terminal positions were prepared in suitable quantities by a Negishi metal cross-coupling procedure. The yields of heterocyclic coupling between 2-pyridyl zinc bromide reagents 12a-c and 2,6-bis(6-trifluoromethanesulfonylpyridazin-3-yl)pyridine increased from 68 to 95% following introduction of electron-donating methyl groups on the metallated halogenopyridine units. Favorable conditions for preparative electrochemical reduction of tripyridyl-dipyridazines 2b,c were established in THF/acetate buffer (pH 4.6)/acetonitrile to give the targeted 2,6-bis[5-(pyridin-2-yl)pyrrol-2-yl]pyridines 1b and 1c in good yields. The absorption behavior of the donor-acceptor tripyridyl-dipyrrole ligands was evaluated and compared to theoretical calculations. Highly fluorescent properties of these chromophores were found (ν(em)≈2 × 10(4) cm(-1) in MeOH and CH(2)Cl(2)), and both pyrrolic ligands exhibit a remarkable quantum yield in CH(2)Cl(2) (φ(f)=0.10). Structural studies in the solid state established the preferred cis conformation of the dipyrrolic ligands, which adopting a planar arrangement with an embedded molecule of water having a complexation energy exceeding 10 kcal mol(-1). The ability of the tripyridyl-dipyrrole to complex two copper(II) ions in a pentacoordinate square was investigated.

Synthesis of 2,3-di- and 2,2,3-trisubstituted-3-methoxycarbonyl-γ-butyrolactones as potent antitumor agents.

Various 2,3-substituted γ-butyrolactones have been synthesized by three-component reaction of aryl bromides, dimethyl itaconate and carbonyl compounds. The in vitro cytotoxic activity of these products was evaluated against a representative panel of cancer cell lines (KB, HCT116, MCF7, MCF7R, PC3, SK-OV3, HL60 and HL60R). One compound (4x) displays a good anti-proliferative activity with IC50 in the sub-micromolar range. The mechanism of action has been investigated using flow cytometry.

Bottom-up preparation of MgH2 nanoparticles with enhanced cycle life stability during electrochemical conversion in Li-ion batteries.

A promising anode material for Li-ion batteries based on MgH2 with around 5 nm average particles size was synthesized by a bottom-up method. A series of several composites containing MgH2 nanoparticles well dispersed into a porous carbon host has been prepared with different metal content up to 70 wt%. A narrow particle size distribution (1-10 nm) of the MgH2 nanospecies with around 5.5 nm average size can be controlled up to 50 wt% Mg. After a ball milling treatment under Ar, the composite containing 50 wt% Mg shows an impressive cycle life stability with a good electrochemical capacity of around 500 mA h g(-1). Moreover, the nanoparticles' size distribution is stable during cycling.

Synthesis of small metallic Mg-based nanoparticles confined in porous carbon materials for hydrogen sorption.

MgH2, Mg-Ni-H and Mg-Fe-H nanoparticles inserted into ordered mesoporous carbon templates have been synthesized by decomposition of organometallic precursors under hydrogen atmosphere and mild temperature conditions. The hydrogen desorption properties of the MgH2 nanoparticles are studied by thermo-desorption spectroscopy. The particle size distribution of MgH2, as determined by TEM, is crucial for understanding the desorption properties. The desorption kinetics are significantly improved by downsizing the particle size below 10 nm. Isothermal absorption/desorption cycling of the MgH2 nanoparticles shows a stable capacity over 13 cycles. The absorption kinetics are unchanged though the desorption kinetics are slower on cycling.

Preparation of functionalized aryl- and heteroarylpyridazines by nickel-catalyzed electrochemical cross-coupling reactions.

A general efficient electrochemical method for the preparation of aryl- and heteroarylpyridazines in a nickel-catalyzed cross-coupling reaction of 3-chloro-6-methoxypyridazine and 3-chloro-6-methylpyridazine with a range of functionalized aryl or heteroaryl halides is reported.

Mixed effect of the supporting electrolyte and the zinc anode in the electrochemical homocoupling of 2-bromopyridines catalyzed by nickel complexes in an undivided cell.

[reactions: see text] Nickel-catalyzed electroreductive homocoupling of 2-bromomethylpyridines and 2-bromopyridine has been investigated in an undivided cell in the presence of a zinc sacrificial anode. A series of reactions were performed with various types and concentrations of supporting electrolyte. It was observed that a key step in this process is the formation of an arylzinc through a nickel-zinc transmetalation. This intermediate can be transformed back to the reactive arylnickel species to afford the homocoupling as the final product. The back process from the arylzinc intermediate is, however, suppressed in the presence of high concentration (0.2 M) of tetraalkylammonium salts. On the contrary, with NaI, the formation of the dimer is not prevented, whatever the NaI concentration.