Jordi Marquet

Nucleophilic Aromatic Substitution of Hydrogen: A Novel Electrochemical Approach to the Cyanation of Nitroarenes

The nucleophilic aromatic substitution of hydrogen through electrochemical oxidation of the intermediate sigma complexes (Meisenheimer complexes) in simple nitroaromatic compounds is reported for the first time. The studies have been carried out with hydride and cyanide anions as the nucleophiles using cyclic voltammetry (CV) and preparative electrolysis. The cyclic voltammetry experiments allow for the detection and characterization of the sigma complexes and led us to a proposal for the mechanism of the oxidation step. Furthermore, the power of the CV technique in the analysis of the reaction mixture throughout the whole chemical and electrochemical process is described.

A dual mechanistic pathway in the alkylation of pentane-2,4-dione through its Co(II) complex

Abstract A mechanistic study on the alkylation of pentane-2,4-dione through its Co(II) complex has shown that a non radical chain mechanism initiated by an electron transfer step induced by Co(II) operates under certain experimental conditions.

Nitrophenyl ethers as possible photoaffinity labels. The nucleophilic aromatic photosubstitution revisited.

Abstract The photoreactions of nitrophenyl ethers with simple primary and secondary amines show a remarkable nucleophile influence on the reaction orientation. Calculations indicate a change from charge controlled to frontier orbital controlled reactions moving from smaller to larger amines.

Mechanistic studies on the reactivity of halodinitrobenzene radical-anion

Abstract The electrochemical behaviour of 1-F-2,4-dinitrobenzene, 1-Cl-2,4-dinitrobenzene and 1-Br-2,4-dinitrobenzene in DMF is described. The 1-F-2,4-dinitrobenzene radical anion dimerises before cleaving, whereas 1-Cl-2,4-dinitrobenzene and 1-Br-2,4-dinitrobenzene radical anions dimerise after cleavage. This change in mechanism allows the obtention of 2,2′,4,4′-tetranitrobiphenyl in a selective way, and with good efficiency. The electrochemical oxidation of σ-complexes is shown to be an alternative means of obtaining products that are difficult to obtain through traditional procedures.

Direct coupling of carbon nucleophiles with m-dinitrobenzene: A novel fluoride promoted nucleophilic aromatic photosubstitution for hydrogen

Abstract Useful yields are achieved in the C-arylation of ketones, nitriles and esters through direct hydrogen nucleophilic aromatic photosubstitution of m-dinitrobenzene, promoted by fluoride anion.

Electrochemical Synthesis of Nitroanilines

Alkylamines and amides are readily prepared by nucleophilic aromatic substitution of hydrogen in nitroarenes by electrochemical oxidation. Useful yields (15−85%) are achieved in a simple direct and regioselective amination process. The synthetic method has been examined in the absence and presence of external bases, used to promote the first step of the nucleophilic aromatic substitution reaction, i.e. the nucleophilic attack. In both cases, good results were obtained. The unreacted starting material can easily be recovered at the end of the electrochemical oxidation process. This new method represents an environmentally favourable route to amino- and amido-substituted nitroaromatic compounds.

Preparation of 3-Pyrrolidone and 4-Perhydroazepinone

Abstract Efficient multigram preparations of 3-pyrrolidone by sequential Michael addition and Dieckmann condensation, and of 4-perhydroazepinone by ring expansion have been achieved.

Electrochemical Synthesis of Nitroaromatic Ketones

Nitroaromatic ketones are readily prepared by nucleophilic aromatic substitution of hydrogen in nitroarenes by electrochemical oxidation. Carbanions of various ketones were added to selected nitroarenes in DMF/ketone mixtures leading to formation of the σH complexes. The reaction was promoted using potassium tert-butoxide as a base. Useful yields were achieved (80−100%) in the C-arylation of ketones. In most cases, the process proceeded with high selectivity. This new method represents an environmentally favourable route for obtaining nitroaromatic ketones.

Efficiency of singlet oxygen generation from the triplet states of nitrophenyl ethers

Abstract The bimolecular rate constants for oxygen quenching, k O 2 T and the quantum yields of singlet oxygen production, Δ , for 4-nitroveratrole, 4-nitroanisole and 3-nitroanisole triplet states in air-equilibrated deuterated water and acetonitrile solutions were determined where possible from nanosecond laser flash photolysis and time-resolved O 2 ( 1 Δ g ) phosphorescence measurements. The results show that the efficiency of singlet oxygen production, ƒ Δ T, for 4-nitroveratrole and 3-nitroanisole is moderately high and is related with the nature of the low-lying triplet state and that 4-nitroanisole is not able to sensitize singlet oxygen under these conditions.

Transition-metal complexes with dehydroacetic acid: Crystal structure of bis(3 - acetyl - 4 - hydroxy - 6 - methyl - 2 - pyrone)cobalt(II) bis(dimethylformamide)

Abstract Co(II), Ni(II), Cu(II) and Cr(III) complexes with monoprotic dehydroacetic acid (3 - acetyl - 4 - hydroxy - 6 - methyl - 2 - pyrone) are described. The Co, Ni and Cu compounds present 1 : 2 metal: ligand ratios and the Cr compound a 1 : 3 ratio. All of these compounds are soluble in dimethylformamide and formed adducts with this solvent. One of these solvates, bis(3 - acetyl - 4 - hydroxy - 6 - methyl - 2 - pyrone)cobalt(II) bis(dimethylformamide), afforded crystals suitable for X-ray diffraction analysis, and its crystalline and molecular structures are reported. The crystals are triclinic, space group P1, with a = 8.290(1), b = 9.570(2), c = 7.731(1) A, α = 94.16(2), β = 101.52(2), γ = 85.15(2)°, V = 597.9(2) A3, Z = 1. Least-squares refinement of the structure based on 3088 observations led to final discrepancy indices of R = 0.075 and Rw = 0.049. The Co atoms lies on a inversion center having distorted octahedral coordination through four O atoms of two 3 - acetyl - 4 - hydroxy - 6 - methyl - 2 - pyrone groups and two O atoms of two dimethylformamide molecules. The 3 - acetyl - 4 - hydroxy - 6 - methyl - 2 - pyrone group is practically planar.