Sodium arenetellurolate-catalyzed reduction of nitroalkanes to oximes

Treatment of aliphatic nitro compounds with NaBH₄ in alkaline ethanol in the presence of a catalytic amount of diaryl ditelluride at 25°C for 5–20 h produces the corresponding oximes, generally as a mixture of E/Z isomers, in fair to good yields. Arenetellurolate anion (ArTe⁻) generated in situ is suggested to be the active species for the reduction.     

1‐Chloro‐2‐nitro­benzene: N—O⋯Cl halogen bonds and aromatic π–π stacking,and thermal vibrations in the vicinity of the melting point

The crystal structure of 1‐chloro‐2‐nitro­benzene, C₆H₄ClNO₂, is made up of mol­ecules which are linked by N—O⋯Cl halogen bonds. These mol­ecular chains are involved in aromatic π–π stacking; the inter­molecular O⋯Cl distance is 3.09 Å. Such short halogen bonds are not common. A rigid‐body analysis including the non‐rigidly attached rigid group provides the mean‐square amplitudes of the mol­ecular translations and librations, and of the inter­nal torsional vibrations of the nitro group. The results reveal the driving role of the torsional vibrations of the nitro group in the phase transition to the liquid phase.     

Determination of the strength of the intramolecular electric field of the NO2 group by the NQR method

Conclusions Comparison of the investigated NQR spectra of the halogen atoms in a series of methane nitro derivatives with the field constants of the halogen atoms makes it possible to estimate the averaged intramolecular electric field created by the NO₂ group.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 769–772, April, 1981.     

Selective reduction of aromatic nitro compounds with stannous chloride in non acidic and non aqueous medium

Aromatic nitro compounds are readily reduced by SnCl₂, 2 H₂O in alcohol or ethyl acetate or by anhydrous SnCl₂ in alcohol where other reducible or acid sensitive groups such as aldehyde, ketone, ester, cyano, halogen and O-benzyl remain unaffected.     

Reactions of Nucleophiles with Nitroarenes: Multifacial and Versatile Electrophiles

In this overview, it is shown that there are many initial reactions between nitroarenes and nucleophiles: addition to the electron‐deficient ring at positions occupied by halogen and hydrogen atoms, addition to the nitro group, single‐electron transfer (SET), and other types of initial reactions. The resulting intermediates react further in a variety of ways to form products of nucleophilic substitution of a halogen atom (S_NAr), a hydrogen atom (S_NArH), and others. Many variants of these processes are briefly discussed, particularly in relation of rates of the initial reactions and further transformations.     

Two different modes of halogen bonding in two 4‐nitroimidazole derivatives

In the crystal structures of the two imidazole derivatives 5‐chloro‐1,2‐dimethyl‐4‐nitro‐1H‐imidazole, C₅H₆ClN₃O₂, (I), and 2‐chloro‐1‐methyl‐4‐nitro‐1H‐imidazole, C₄H₄ClN₃O₂, (II), C—Cl...O halogen bonds are the principal specific interactions responsible for the crystal packing. Two different halogen‐bond modes are observed: in (I), there is one very short and directional C—Cl...O contact [Cl...O = 2.899 (1) Å], while in (II), the C—Cl group approaches two different O atoms from two different molecules, and the contacts are longer [3.285 (2) and 3.498 (2) Å] and less directional. In (I), relatively short C—H...O hydrogen bonds provide the secondary interactions for building the crystal structure; in (II), the C—H...O contacts are longer but there is a relatively short π–π contact between molecules related by a centre of symmetry. The molecule of (I) is almost planar, the plane of the nitro group making a dihedral angle of 6.97 (7)° with the mean plane of the imidazole ring. The molecule of (II) has crystallographically imposed mirror symmetry and the nitro group lies in the mirror plane.     

A simple deprotection of triflate esters of phenol derivatives

Efficient conversion of aryl triflates into the corresponding phenols has been accomplished with Et₄NOH. In contrast to other cleavage reactions, such functional groups as nitro, ketone, halogen, amide and sulfonamide groups were intact under the reaction conditions. This mild removal of the trifluoromethanesulfonyl group would serve a new protecting group of phenols.     

Palladium catalyzed C-allylation of nitroalkanes

A detailed study of palladium catalyzed C-allylation of aliphatic nitro compounds is described. Allylic alcohols and/or their acetates and allyl phenyl ethers were employed as allylating agents. The dependence of the reaction yield on nature and quantity of base and structure of the allylic unit is reported and explained. The lowest yield was obtained for allyl alcohol; however it could be considerably increased by addition of a stoichiometric amount of ethyl acetate. Order of reactivity of functions groups was OPh > OAc > OH. A novel method of synthesis of tetrakis (triphenylphosphine) palladium is also reported.     

Allyl tetrahydropyranyl ether: a versatile alcohol/thiol protecting reagent

Allyl tetrahydropyranyl ether (ATHPE) can be used as a versatile protecting reagent. In combination with NBS/I₂, O-allyl group can easily be replaced by hydroxyls (including tertiary-OH) or thiols, in the molecules comprising other reactive functional groups such as halogen, nitro, acetonide and alkene under mild reaction conditions (near neutral pH and ambient temperature).     

Research on five-membered heterocycles

Replacement of the nitro group in polynitroimidazoles by a halogen atom by the action of POBr₃ in dimethylformamide or by means of hydrohalic acids was studied. It is shown that the second method is the most convenient method in the preparation of chloro- and bromonitroimidazoles.See [1] for communication I.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1666–1668, December, 1977.     

Research on five-membered heterocycles

Nitrochloroimidazoles were synthesized by replacement of the nitro group in dinitroimidazoles by chlorine by the action of POCl₃. It is shown that in the case of 4,5-dinitroimidazoles substitution takes place when both dimethylformamide (DMF) and pyridine are used as the solvents, while only DMF is suitable for 2,4-dinitroimidazoles. The location of the halogen in the synthesized nitrochloroimidazoles was confirmed by alternative synthesis.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, May, 1977.     

‘On water’ synthesis of 2,4-diaryl-2,3-dihydro-1,5-benzothiazepines catalysed by sodium dodecyl sulfate (SDS)

An efficient synthesis of 1,3-diaryl-2,3-dihydro-1,5-benzothiazepines has been developed by the reaction of various 1,3-diaryl-2-propenones with 2-aminothiophenol in water under neutral conditions catalysed by SDS. Excellent chemoselectivity was observed for substrates possessing halogen atoms or nitro/alkoxy/thioalkyl groups which did not undergo competitive aromatic nucleophilic substitution of the halogen atoms or the nitro group, reduction of the nitro or the α,β-unsaturated carbonyl group, or dealkylation of the alkoxy/thioalkoxy groups.     

Chemo-, site-selective reduction of nitroarenes under blue-light,catalyst-free conditions

The tandem reaction of photoinduced double hydrogen-atom transfer and deoxygenative transborylation for chemo-and site-selective reduction of nitroarenes into aryl amines under catalyst-free, room temperature conditions was disclosed in excellent yields. In this reaction, isopropanol（ⁱPrOH） was used as hydrogen donor and tetrahydroxydiboron [B₂（OH）₄] as deoxygenative reagent with green, cheap, and commercially available credentials. In particular, a wide range of...     

1‐(4‐Bromo­phenyl)‐2‐methyl‐4‐nitro‐1H‐imidazole: bifurcated Br⋯O halogen–nitro bonds

The crystal packing of the title compound, C₁₀H₈BrN₃O₂, is determined mainly by relatively strong bifurcated C—Br⋯O halogen–nitro bonds. Both O atoms are involved in this interaction in an almost symmetrical manner and the difference [0.078 (3) Å] between the Br⋯O contact lengths is one of the smallest found in similar compounds. Halogen bonds and weak hydrogen bonds connect mol­ecules into layers which are stacked along the [100] direction.     

One-pot preparation of azobenzenes from nitrobenzenes by the combination of an indium-catalyzed reductive coupling and a subsequent oxidation

We demonstrated how a reduction step with a reducing system comprised of In(OTf)₃ and Et₃SiH and a subsequent oxidation that occurred under an ambient (oxygen) atmosphere allowed the highly selective and catalytic conversion of aromatic nitro compounds into symmetrical or unsymmetrical azobenzene derivatives. This catalytic system displayed a tolerance for the functional groups on a benzene ring: an alkyl group, a halogen, an acetyl group, an ester, a nitrile group, an acetyl group, an ester moiety, and a sulfonamide group.     

Catalytic, PMe3-mediated conversion of secondary nitroalkanes to ketones: a very mild Nef-type process

Aliphatic secondary nitro compounds are converted to ketones at room temperature, usually in 90-100% yields, by a one-pot reaction with 220-250 mol % of trimethylphosphine (PMe₃) and 50-100 mol % of ^tBuC₆H₄SSC₆H₄^tBu or PhthN-SePh, or 20 mol % of both additives. Thus, very mild catalytic variants of the reductive Nef-like reactions are disclosed.     

Cyano–cyano and chloro–cyano interactions in two imidazole derivatives

In two closely related 1‐aryl‐2‐methyl‐4‐nitro‐5‐cyano­imid­azoles, namely 2‐methyl‐4‐nitro‐1‐phenyl‐1H‐imidazole‐5‐carbo­nitrile, C₁₁H₈N₄O₂, and 1‐(4‐chloro­phenyl)‐2‐methyl‐4‐nitro‐1H‐imidazole‐5‐carbo­nitrile, C₁₁H₇ClN₄O₂, different weak intermolecular interactions determine the crystal packing. In the 1‐phenyl derivative, dipole–dipole interactions between antiparallel cyano groups connect mol­ecules into centrosymmetric dimers, while in the 1‐(4‐chloro­phenyl) derivative, the dimers are connected by C≡N⋯Cl—C halogen bonds. These interactions, together with weak C—H⋯O(N) hydrogen bonds, connect mol­ecules related by subsequent centres of inversion into infinite tapes.     

Chemoselective SN2′ reaction of nitroalkanes to dialkyl 2-(bromomethyl)fumarates under cetyltrimethylammonium hydroxide (CTAOH) catalysis

The chemoselective S_N2′ reaction of a variety of primary nitroalkanes to dialkyl 2-(bromomethyl)fumarates can be efficiently performed under cetyltrimethylammonium hydroxide (CTAOH) catalysis. The α,β-unsaturated esters were obtained in satisfactory to good yields with the complete retention of the nitro group.     

Monofluoration quantitative par le phenyltetrafluorophosphorane influence de la température

The monofluorination by substitution of the hydroxyl group of the β-hydroxyesters of (o, m, p) Z - C₆H₄ - C(OH)R - CH R′ - COOR″ structure (where Z = halogen, methyl, methoxy, nitro and H) of 2,2,2 trichloroarylcarbinols by the phenyl tetrafluorophosphorane is described. The temperature at which the alkoxytrifluorophosphorane is decomposed, determines the nature (alkene alkoxytrifluorophosphorane, monofluorinated compounds) of the products and their yield. Knowledge of this temperature for erythro and threo isomers permits the selective fluorination of one them in a mixture.     

Competing intermolecular interactions in some `bridge‐flipped' isomeric phenylhydrazones

To examine the roles of competing intermolecular interactions in differentiating the molecular packing arrangements of some isomeric phenylhydrazones from each other, the crystal structures of five nitrile–halogen substituted phenylhydrazones and two nitro–halogen substituted phenylhydrazones have been determined and are described here: (E)‐4‐cyanobenzaldehyde 4‐chlorophenylhydrazone, C₁₄H₁₀ClN₃, (Ia); (E)‐4‐cyanobenzaldehyde 4‐bromophenylhydrazone, C₁₄H₁₀BrN₃, (Ib); (E)‐4‐cyanobenzaldehyde 4‐iodophenylhydrazone, C₁₄H₁₀IN₃, (Ic); (E)‐4‐bromobenzaldehyde 4‐cyanophenylhydrazone, C₁₄H₁₀BrN₃, (IIb); (E)‐4‐iodobenzaldehyde 4‐cyanophenylhydrazone, C₁₄H₁₀IN₃, (IIc); (E)‐4‐chlorobenzaldehyde 4‐nitrophenylhydrazone, C₁₃H₁₀ClN₃O₂, (III); and (E)‐4‐nitrobenzaldehyde 4‐chlorophenylhydrazone, C₁₃H₁₀ClN₃O₂, (IV). Both (Ia) and (Ib) are disordered (less than 7% of the molecules have the minor orientation in each structure). Pairs (Ia)/(Ib) and (IIb)/(IIc), related by a halogen exchange, are isomorphous, but none of the `bridge‐flipped' isomeric pairs, viz. (Ib)/(IIb), (Ic)/(IIc) or (III)/(IV), is isomorphous. In the nitrile–halogen structures (Ia)–(Ic) and (IIb)–(IIc), only the bridge N—H group and not the bridge C—H group acts as a hydrogen‐bond donor to the nitrile group, but in the nitro–halogen structures (III) (with Z′ = 2) and (IV), both the bridge N—H group and the bridge C—H group interact with the nitro group as hydrogen‐bond donors, albeit via different motifs. The occurrence here of the bridge C—H contact with a hydrogen‐bond acceptor suggests the possibility that other pairs of `bridge‐flipped' isomeric phenylhydrazones may prove to be isomorphous, regardless of the change from isomer to isomer in the position of the N—H group within the bridge.