Development of chemoselective photoreduction of nitro compounds under solar light and blue LED irradiation

Solar light and blue light irradiation of the commercially available heterogeneous nano photocatalyst TiO₂–P25 leads to reduction of nitro compounds to give the corresponding amines. The methodology provides a green and mild approach to this useful class of organic compounds. Aromatic nitro compounds containing a wide range of functional groups tolerated the conditions to give, chemoselectively the corresponding amines in excellent yields.     

Photocatalytic reduction of nitro aromatic compounds to amines using a nanosized highly active CdS photocatalyst under sunlight and blue LED irradiation

A variety of aromatic nitro compounds were chemoselectively reduced to the corresponding anilines using conveniently prepared nanosized CdS as a photocatalyst under the sunlight and blue LED irradiation. The results demonstrated that synthesized CdS nanostructures have the potential to provide a promising visible light driven photocatalyst for chemoselective reduction of nitro aromatics in the presence of nitrile and carbonyl groups to the corresponding amines under both sunlight and blue LED irradiation. Photoreduction of nitro aromatics by the prepared nanosized CdS with high surface area was faster than when using the commercially available CdS under both sunlight and LED irradiation. Nanosized CdS photocatalyst was prepared by a simple method without any capping agent. X-ray diffraction (XRD), energy dispersive spectrometry (EDAX), transmission electron microscopy (TEM), scanning electron microscopy (SEM), N₂ absorption—desorption, diffuse reflectance spectroscopy (DRS), and flat band potential methods were employed for the characterization, which revealed that the prepared CdS nanoparticles have a well-resolved cubic structure with the size of around 10–30 nm and a band gap of 2.37 eV.     

A constructive synthetic approach for reduction of nitro heterocyclics- characterization and degradation studies

A novel synthetic approach was proposed for a metal free reduction of nitro aromatic compounds to the resultant amines by sodium dithionite. A series of nitro compounds containing various reducible functional groups were chemoselectively reduced in good to excellent yield. Instantaneously some of the products are chemically degraded and all are characterized by spectral methods.     

Reduction processes biocatalyzed by Vigna unguiculata

Whole cells from the Brazilian beans feijão de corda (Vigna unguiculata) have been employed as biocatalysts in different bioreduction processes. Good to excellent selectivities can be obtained in the reduction of aromatic and aliphatic ketones, as well as β-ketoesters, depending on the conversions and the chemoselectivity on the substrate structure. This biocatalyst was also able to reduce the nitro moiety of different aromatic nitro compounds, showing as well enoate reductase activity, and chemoselectively catalyzing the double bond reduction of 4-phenyl-3-buten-2-one with moderate conversion.     

A convenient synthesis of deuterium labeled tertiary aliphatic nitro ketones and nitriles - starting materials for preparation of deuterated cyclic nitrones, isomeric hydroxylamines, and corresponding C-nitroso compounds

Tertiary aliphatic β- and γ-nitro nitriles and ketones deuterated in (several) selected positions had been synthesized. The deuterated nitro compounds served as a starting material for the corresponding deuterium labeled nitrones or hydroxylamines (reducing with aluminum amalgam). Further oxidation of the last two groups of compounds with sodium periodate or m-CPBA afforded the relevant deuterated tertiary C-nitroso compounds.     

High performance liquid chromatographic determination of diazinon, permethrin, DEET (N, N-diethyl-m-toluamide), and their metabolites in rat plasma and urine

A rapid method was developed for the analysis of the insecticide (A) diazinon (O,O-diethyl O-2-isopropyl-6-methylpyridimidinyl) phosphorothioate, its metabolites (B) diazoxon (O,O-diethyl O-2-isopropyl-6-methylpyridimidinyl) phosphate, and (C) 2-isopropyl-6-methyl-4-pyrimidinol, the insecticide (D) permethrin [3-(2,2-dichloro-ethenyl)-2,2-dimethylcyclopropanecarboxylic acid (3-phenoxyphenyl)methylester], its metabolites (E) m-phenoxybenzyl alcohol, and (F) m-phenoxybenzoic acid, the insect repellent (G) DEET (N,N-diethyl-m-toluamide), and its metabolites (H) m-toluamide and (I) m-toluic acid in rat plasma and urine. The method is based on using C₁₈ Sep-Pak cartridges (Waters Corporation, Milford, Mass., U.S.A.) for solid phase extraction and high performance liquid chromatography with a reversed phase C₁₈ column, and absorbance detection at 230 nm for compounds A, B, and C, and at 210 nm for compounds D–I. The compounds were separated using a gradient from 1% to 99% acetonitrile in water (pH 3.0) at a flow rate ranging between 1 and 1.7 mL/min in a period of 17 min. The limits of detection were ranged between 20 and 100 ng/mL, while limits of quantification were 80–200 ng/mL. The relationship between peak areas and concentration was linear over a range of 100–1000 ng/mL. This method was applied to determine the above insecticides and their metabolites following dermal administration in rats.     

Chemoselective reduction of β-butyltellanyl α,β-unsaturated carbonyl compounds to allylic alcohols

(Z)-β-Butyltellanyl α,β-unsaturated carbonyl compounds were stereoselectively produced by hydrotelluration of alkynones or by an addition/elimination sequence from enol tosylates. The β-butyltellanyl-enones were chemoselectively reduced with NaBH₄/MeOH, NaBH₄·CeCl₃·7H₂O/MeOH and DIBAL-H systems to the corresponding allylic alcohols with retention of the Z stereochemistry.     

Effect of Medium Basicity on the Coordination Kinetics of <Emphasis Type="Italic">meso</Emphasis>-Nitro-Substituted Derivatives of 5-Phenyl-β-Octaalkylporphine with Zinc Acetate

The kinetics of formation of zinc complexes of 10,15-dinitro-5-phenyl-2,3,7,8,12,13,17,18-octamethylporphine, 10,15,20-trinitro-5-phenyl-2,3,7,8,12,13,17,18-octamethylporphine, and 10,15,20-trinitro-5-(4-nitro-phenyl)-2,3,7,8,12,13,17,18-octamethylporphine were studied spectrophotometrically at 288–308 K in Zn(OAc)₂–acetonitrile and Zn(OAc)₂–1,8-diazabicyclo[5.4.0]-undec-7-en–acetonitrile solutions with different basicities. The compounds under study were identified by electronic absorption, IR and ¹H NMR spectroscopies. An analysis of the effect of nitro groups on the kinetics of coordination of Zn(II) with the studied ligands showed that the changes in complexing properties of nitro derivatives of 5-phenyl-β-octaalkylporphine are related to the electron-withdrawing effect of NO₂ groups, to structural effects of distortion of the planar structure of the macrocycle, and to alteration of basicity of the reaction medium.     

Deoxyfluorination of alcohols using N,N-diethyl-α,α-difluoro-(m-methylbenzyl)amine

Deoxyfluorination of alcohols was carried out using N,N-diethyl-α,α-difluoro-(m-methylbenzyl)amine (DFMBA). Primary alcohols were effectively converted to fluorides under microwave irradiation or conventional heating. Deoxyfluorination of an anomeric hydroxy group in sugars by DFMBA proceeded at below room temperature and glycosyl fluorides could be obtained in good yields. The deoxyfluorination reaction chemoselectively proceeded and various protecting groups on the sugar can survive under the reaction conditions.     

Selective synthesis of fluorinated carbohydrates using N,N-diethyl-α,α-difluoro-(m-methylbenzyl)amine

Deoxyfluorination of a hydroxy group in carbohydrates was carried out using N,N-diethyl-α,α-difluoro-(m-methylbenzyl)amine. A primary hydroxy group in carbohydrates was effectively converted to the corresponding fluoride under microwave irradiation or at 100 °C. Deoxyfluorination of hydroxy groups at the anomeric position proceeded at below room temperature, and glycosyl fluorides could be obtained in good yields. The reaction chemoselectively proceeded, and various protecting groups of carbohydrates can survive under the reaction conditions.     

1‐(2‐Hydroxyethyl)‐3‐nitro‐1, 2, 4‐triazole and its Complexes with Copper(II) Chloride and Copper(II) Perchlorate

1‐(2‐Hydroxyethyl)‐3‐nitro‐1, 2, 4‐triazole (hnt), prepared by alkylation of 3‐nitro‐1, 2, 4‐triazole with 2‐chloroethanol, was found to react with copper(II) chloride and copper(II) perchlorate in acetonitrile/ethanol solutions giving complexes [Cu₂(hnt)₂Cl₄(H₂O)₂] and[Cu(hnt)₂(H₂O)₃](ClO₄)₂, respectively. They are the first examples of coordination compounds with a neutral N‐substituted 3‐nitro‐1, 2, 4‐triazole ligand. 1‐(2‐Hydroxyethyl)‐3‐nitro‐1, 2, 4‐triazole and the obtained complexes were characterized by NMR and IR spectroscopy, X‐ray, and thermal analyses. [Cu₂(hnt)₂Cl₄(H₂O)₂] presents a dinuclear chlorido‐bridged complex in which hnt acts as a chelating bidentate ligand, coordinated to the metal by a nitrogen atom of the triazole ring and an oxygen atom of the nitro group, and the copper atoms are inconsiderably distorted octahedral coordination. [Cu(hnt)₂(H₂O)₃](ClO₄)₂comprises a mononuclear complex cation, in which two nitrogen atoms of two hnt ligands in trans configuration and three water oxygen atoms form a square pyramidal environment around the copper atom, which is completed to an distorted octahedron with a bifurcated vertex due to two additional elongated Cu–O bonds with two nitro groups. In both complexes, Cu–O bonds with the nitro groups may be considered as semi‐coordinated.     

Synthesis and photoluminescence properties of π-extended fluorene derivatives: the first example of a fluorescent solvatochromic nitro-group-containing dye with a high fluorescence quantum yield

Functional π-extended fluorene derivatives, 2,7-di(p-substituted-phenyl)fluorenes containing different functional groups such as hydrogen, trimethylsilyl (TMS), methoxycarbonyl, cyano, and nitro groups, were synthesized. Except for the nitro group, the resulting compounds exhibited extremely high fluorescence quantum yields (Φ_F >0.85 in chloroform). The diphenylfluorene containing nitro groups have higher fluorescence quantum yield (Φ_F = 0.31 in N,N’-dimethyl-formamide) than other nitro-group-containing fluorophores which were previously reported (Φ_F <0.1). Furthermore, this compound exhibited large Stokes’ shift with green to orange emission and unique on-off behavior of the emission by solvents.     

Submerged electric arc between graphite electrodes: a one-pot tool for the synthesis of long-chain polyynes in solution

Polyynes, a class of molecules described by the general formula H-(CC)_mH (where m is an integer) can be synthesized using an electric arc between graphite electrodes submerged in an organic solvent such as methanol, n-hexane, n-dodecane, decahydronaphthalene or acetonitrile. When the electric arc is used in acetonitrile at −40 °C, polyyne chains of up to 18 carbon atoms (m=9) have been produced together with monocyanopolyyne as by-product. The polyynes can be reduced to ene-ynes by shaking a hexane solution of them with Zn/HCl.     

Apparent donor-acceptor interaction between nitroaromatics and acetonitrile

The partitioning behavior of nitro-aromatics in octanol-water and acetonitrile/NaCl-saturated water was examined. The nitro group contribution is opposite in the two systems, from which two different bonding mechanisms were inferred. In addition to cavity effects the octanol-water system is characterized by H-bonding of water to the nitro groups, while in the acetonitrile/NaCl-saturated water system electron donor-acceptor complexation predominates. A linear free energy relationship which relates the partition coefficients in the two systems was logP _aw =0.727 logP _ow +0.395 n+0.742 where n is the number of nitro groups per ring.     

A mass spectral study of some symmetric and unsymmetric sulfides,disulfanes, and trisulfanes

The low-resolution mass spectra of 13 trifluoromethyl and/or methyl sulfur-containing compounds (CF₃S_nCF₃, CF₃S_nCH₃, CH₃S_nCH₃, CF₃S_mCl, and CH₃S_mCl; n = 1, 2, 3; m = 1, 2) are reported and discussed. There is a considerable similarity between the fragmentation pattern of compounds with the same terminal groups. However, with a fluorinated and a non-fluorinated methyl group, the major fragmentation products produced are similar to those for the dimethyl compounds.     

Palladium-catalyzed intramolecular α-arylation of aliphatic ketone, formyl, and nitro groups

Intramolecular arylation of properly designed substrates bearing a ketone, formyl, or nitro terminating group was achieved by use of a PdCl₂(Ph₃P)₂-Cs₂CO₃ reaction system to form a variety of carbocyclic compounds. Arylation in ketone compounds afforded benzene-annulated bridged or spirocycloalkanone derivatives, depending on the structure of the cyclization precursors. Arylation in formyl compounds occurred at the α-position (α-arylation) or at the carbonyl carbon (carbonyl-arylation) depending on the structure of the cyclization precursors and on the reaction solvent. An α-arylated secondary nitro group was partially transformed to ketone in the manner of the Nef reaction, whereas a tertiary nitro group was partially eliminated to afford a styrene-type olefin.     

Mass spectra of some α-substituted phenyl-α,α′-dimethoxyl ketones and their derivatives

The mass spectra of some α-substituted phenyl-α,α′-dimethoxyl ketones (compounds 1) and their 2,4-dinitrophenylhydrazones (compounds 2) and semicarbazones (compounds 3) have been studied. The characteristic fragments at m/z (M ? 73) from compounds 1, m/z (M ? 253) from compounds 2 and m/z (M ? 130) from compounds 3 are abundant and proposed to be [ArCROCH₃]⁺. Fragmentations yielding [M⁺ ? 49] from compounds 2 are abnormal and probably involve the methoxyl and nitro groups. The intense peak at m/z 130 due to [CH₃OCH₂CNNHCONH₂]⁺ from compounds 3 corresponds to α-cleavage of the molecular ion. Some other fragments from these new compounds are interpreted in this paper.     

Synthesis and spectrophotometry study of the acid-base properties of nitro-substituted 5-phenyl-β-octaalkylporphines

10,15-Dinitro-5-phenyl-2,3,7,8,12,13,17,18-octamethylporphine, 10,15,20-trinitro-5-phenyl-2,3,7,8,12,13,17,18-octamethylporphine, and 10,15,20-trinitro-5-(4-nitrophenyl)-2,3,7,8,12,13,17,18-octamethylporphine were synthesized and identified by electronic absorption, IR, and ¹Н NMR spectroscopy. The acid–base properties of the synthesized compounds were studied by spectrophotometric titration in HClO₄–acetonitrile and 1,8-diazabicyclo[5.4.0]undec-7-ene–acetonitrile systems at 298 K. Parameters of the electronic absorption spectra and concentration ranges of existence of the mono- and diprotonated, as well as mono- and dideprotonated forms of the corresponding ligands and the acid and base dissociation constants of the latter were determined. Comparative analysis of the effect of nitro groups on the reactivity of the synthesized compounds was performed.     

Investigations into the selective oxidation of vicinal diols to α-hydroxy ketones with the NaBrO3/NaHSO3 reagent: pH dependence, stoichiometry, substrates and origin of selectivity

The NaBrO₃/NaHSO₃ reagent is one of the few oxidizing agents that chemoselectively oxidizes vicinal diols to α-hydroxy ketones with little overoxidation to the corresponding vicinal-dione or dicarboxylic acid. Oxidation reactions performed with this reagent showed strong pH dependence. cis-Vicinal diols reacted faster than trans-vicinal diols to the α-hydroxy ketone product. Hydroxy functional groups at axial ring positions were more readily oxidized than equatorial hydroxy groups. The application of the NaBrO₃/NaHSO₃ reagent for the chemoselective oxidation of vicinal diols was limited to simple systems and failed with more complex monosaccharide compounds probably due to acid catalyzed dehydrogenation reactions. Despite the simple reaction set-up and good selectivity towards the α-hydroxy ketone product, the actual oxidation reaction mechanism is highly complex and postulated to involve at least six different equilibria with a plethora of bromine containing species. A possible oxidation reaction mechanism is discussed.     

NAD(P)+-NAD(P)H model. 52. Reduction of olefins by hantzsch ester on silica gel

Olefinic double bonds in α,β-unsaturated carbonyl or nitro compounds are reduced chemoselectively by Hantzsch ester on silica gel in excellent yields.