A unique autocatalytic process and evidence for a concerted-stepwise mechanism transition in the dissociative electron-transfer reduction of aryl thiocyanates

Electrochemical reduction of p-methyl-, p-methoxy-, and 3,5-dinitrophenyl thiocyanates as well as p-methyl- and p-methoxyphenyl disulfides was investigated in acetonitrile at an inert electrode. This series of compounds reveals a striking change in the reductive cleavage mechanism of the S-CN bond in thiocyanates as a function of the substituent on the aryl ring of the aryl thiocyanate. With nitro substituents, a stepwise mechanism, with an anion radical as the intermediate, takes place. When electron-donating groups (methyl and methoxy) are present, voltammetric as well as convolution analyses provide clear evidence for a transition between the concerted and stepwise mechanisms based on the magnitude of the transfer coefficient alpha. Moreover, a very interesting autocatalytic process is involved during the electrochemical reduction of these compounds. This process involves a nucleophilic substitution reaction on the initial aryl thiocyanate by the electrochemically generated arenethiolate ion. As a result of this unusual process, the electrochemical characteristics (peak potential and peak width) of the investigated series are concentration dependent.     

BER催化还原一些含氮功能基化合物的研究

用强碱性阴离子交换树脂制备了硼氢阴离子交换树脂还原剂(BER),使其在氯化铜等金属化合物的催化下还原一些芳香硝基、氰基、氮氮双键等含氮功能基化合物.还研究了BER的制备条件:如温度、溶剂、不同金属化合物对还原反应的影响,并初步探讨其反应机理.     

One-step double reduction of aryl nitro and carbonyl groups using hydrazine

Single-step reduction of aryl nitro and carbonyl groups to the corresponding synthetically useful alkyl-anilines occurs with excellent yields by treatment with hydrazine and a base in a solvent-free reaction. The method has been applied to a broad range of compounds with different properties. Investigations into the mechanism of the reduction reveal that each group is reduced independently. A mechanism is proposed for this novel reduction of aromatic nitro groups.     

Catalytic deoxygenation of organic compounds by carbon monoxide: III. The reaction under pressure of aromatic nitro compounds in the presence of o-phthalaldehyde

The reaction of o-phthalaldehyde with several aromatic nitro compounds in the presence of carbon monoxide and catalytic quantities of hexarhodium-hexadecacarbonyl eventuated in the formation of the corresponding N-substituted isoindolinone as the major product. A reaction mechanism has been suggested incorporating deoxygenation of the nitro compound by carbon monoxide to a nitrene intermediate and the subsequent interception of the latter by o-phthalaldehyde.     

Orientation and mechanism of reactions of aromatic amines with sulfur monochloride

The reaction of m-substituted anilines with sulfur monochloride has been studied. It has been shown that cyclization with the formation of 1, 3, 2-benzothiazathiolium compounds takes place in the position para to the substituent. The introduction of methoxy groups into o-nitroanilines interferes with the displacement of the nitro group by the chlorine atom. A nucleophilic reaction mechanism has been proposed according to which the nitro group is displaced after the formation of the thiathioniaazine ring.     

One‐Pot Synthesis of Aliphatic Nitro Compounds by Michael/retro‐Claisen Fragmentation Domino Reaction

A novel and concise method for the construction of γ‐nitro ketones and 1,3‐dinitro compounds with chemoselective acyl transfer has been presented under basic conditions via one‐pot reactions. These reactions feature high atom‐ and step‐economic possess, mild condition and simple operation for one‐pot synthesis of aliphatic nitro compounds. This protocol provides the products in good yields. The possible reaction mechanism has also been proposed.     

Synthesis of 4,5-dihydroisoxazoles by condensation of primary nitro compounds with alkenes by using a copper/base catalytic system

A new procedure for the synthesis of 4.5-dihydroisoxazoles by condensation of primary nitro compounds with olefins by using a copper/base catalytic system is described. The catalytic effect of copper(II) salts is evidenced by comparison of the reaction rates. Thus, activated nitro compounds react faster than with organic catalysis by tertiary amines, whereas nitroalkanes, unable to condense with dipolarophiles in the presence of the base alone, undergo the reaction on addition of a copper(II) catalyst. The observed occurrence of induction periods in most reactions is ascribed to an equilibrium preceding the rate-determining step, and gives a hint as to the proposed reaction mechanism. The results indicate that this method might be of practical and general utility for synthetic practice.     

Diethyl chlorophosphite: a versatile reagent

Diethyl chlorophosphite (DECP) was previously described as a reducing agent for nitro compounds to the corresponding amines (Fischer, B.; Sheihet, L. J. Org. Chem. 1998, 63, 393). Here, the utility of this reagent was extended to chemical conversions of other oxygenated functional groups. In this paper we report on the scope of the reaction of DECP with N-oxides, epoxides, sulfones, sulfoxides, hydroxylamines, ketoximes, and aldoximes. The chemoselectivity of DECP is described, and conditions for a stepwise multiple conversion of functional groups on the same molecule with this reagent are provided.     

Stepwise and concerted pathways in photoinduced and thermal electron-transfer/bond-breaking reactions. experimental illustration of similarities and contrasts.

The electrochemical (cyclic voltammetry) and photoinduced (fluorescence quenching, quantum yields) reductive cleavages of four compounds, 4-cyano-alpha-trifluorotoluene (1), dimethylphenyl sulfonium (2), 4-cyanobenzylmethylphenyl sulfonium (3), and 4-cyanobenzyl chloride (4), are investigated and compared in terms of concerted vs stepwise mechanisms. Bearing in mind that an increase of the thermodynamic driving force shifts the mechanism from concerted to stepwise and that the driving force is larger under photochemical than under electrochemical conditions, 1 and 2 are typical examples where a stepwise mechanism is followed with compatible kinetic characteristics under both regimes. 4 undergoes a concerted electrochemical reductive cleavage, and the same mechanism is followed in the photoinduced reaction with consistent kinetic characteristics. The case of 3 is of particular interest, since a trend of passing from a concerted to a stepwise mechanism when going from the electrochemical to the photochemical conditions indeed appears upon analysis of the experimental results. The change of mechanism is, however, not complete since, in the photoinduced reaction, there is a balanced competition between the two pathways. In the same families of compounds, the unsubstituted benzylmethylphenyl sulfonium cations shows such a borderline behavior during the electrochemical reaction. In the photoinduced reaction, it is the 4-cyano derivative which behaves in a borderline manner, in line with the fact that it gives rise more readily to a concerted mechanism than the unsubstituted compound.     

Preparation of Acyclic Nitro Olefins from β-Trimethylsiloxy Nitro Compounds

An efficient process for the preparation of acyclic nitro olefins is described, which consisted of improved nitro aldol reaction to give β-trialkylsiloxy nitro compounds and the direct or indirect elimination of water.     

Trimethylsilyl derivatives of aliphatic nitro compounds in α,β-C,C-cross-coupling

A new α,β-C,C-cross-coupling reaction of derivatives of aliphatic nitro compounds, silyl nitronates andN,N-bis(silyloxy)enamines, leading to β-nitro oximes was found. The scope and limitations of this reaction were studied, and a mechanism was proposed.     

An efficient in situ reduction and cyclization reaction for synthesis of spiro compound derivatives in Fe–H2O–AcOH medium from nitro compounds

An efficient in situ reduction and cyclization reaction for the synthesis of nitrogen‐containing spiro compounds directly form 5‐nitro‐1H‐indazole, 6‐nitro‐1H‐indazole and 5‐nitroindole in Fe–H₂O–AcOH medium is reported. 5‐Nitro‐1H‐indazole, 6‐nitro‐1H‐indazole and 5‐nitroindole were first used to synthesize spiro compounds, and this is a novel method for the synthesis of spiro compounds from nitro compounds. The advantages of this reaction are stable reagents, easily available raw materials, wide range of substrates and high yields.     

Geminal (difluoroamino)nitro compounds

A novel preparative method for the synthesis of geminal (difluoroamino)nitro compounds was developed, The method involves the reaction ofN,N-difluoro-O-fluorosulfonyl- hydroxylamine with the corresponding salts of nitro compounds, Dependences of the yields of (difluoroamino)nitro compounds on the reaction conditions, the nature of the cation in the salts, and the properties of solvents were studied.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 11. pp. 2689–2692, November, 1996.     

1,8—萘酐和1,8—萘酰亚胺中硝基和卤素基团的亲核取代反应

研究了１，８－萘酐和１，８－萘酰亚胺萘环上硝基和卤素原子的亲核取代反应，讨论了影响亲核取代反应的因素，根据２，４－二硝基苯酚与脂胺肪的亲核取代机理，提出了４－硝基－１，８－萘酐及４－硝基－１，８－萘酰亚胺与脂肪胺发生亲核取代反应可能的反应机理。     

SnCl2／Cu-Mediated Carbonyl Allylation Reaction in Water： Scope, Selectivity and Mechanism

Copper was found to be able to promote the SnC12-mediated carbonyl allylation reactions in water, giving the corresponding homoallylic alcohol products in very high yields. Detailed studies showed that the reaction could be applied to a variety of carbonyl compounds including those with hydroxyl, amino and nitro groups. It was also found that this reaction showed good regioselectivities for some substrates. Furthermore, carefully controled experiments and in situ NMR measurements provided important insights into the mechanism of the newly developed reaction.     

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.     

Stereoselective approach to conjugated enone oximes from aliphatic nitro compounds and sulfur ylides

A novel approach to conjugated enone oximes from aliphatic nitro compounds deals with double silylation of N,N-bis(silyloxy) enamines followed by a stereoselective reaction with an ester-stabilized sulfur ylide. The proposed mechanism involves the generation of labile nitrosoalkenes as intermediates, which react with the sulfur ylide to give target enone oximes.     

Catalyst‐Free Reductive Coupling of Aromatic and Aliphatic Nitro Compounds with Organohalides

A rare reductive coupling of nitro compounds with organohalides has been realized. The reaction is initiated by a partial reduction of the nitro group to a nitrenoid intermediate. Therefore, not only aromatic but also aliphatic nitro compounds are efficiently transformed into monoalkylated amines, with organohalides as the alkylating agent. Given the innate reactivity of the nitrenoid, a catalyst is not required, resulting in a high tolerance for aryl halide substituents in both starting materials.     

Conversion of N-aromatic amides to O-aromatic esters

[reaction: see text] N-Aromatic secondary amides can be transformed into O-aromatic esters in high yield via N-nitrosamide intermediates. The amides can be generated in situ from the corresponding aromatic amines or nitro compounds, and phenols can easily be made from the esters. The reaction can be modified by addition of methyl methacrylate or toluene at 0 degrees C to give polymerization or deamination, respectively. The rearrangement mechanism may involve radical formation and recombination.     

Reactions of organic anions—L : Reactions of phenylacetonitrile derivatives with aromatic nitrocompounds in basic media

Reaction of phenylalkanenitriles and diphenylacetonitrile with aromatic nitro compounds were studied using various base-solvent systems. Four independent types of reaction: substitution of halogen, substitution of nitro group, substitution of hydride anion and electron transfer were observed. Relationship—reaction pathway—conditions have been discussed.