The Electrochemical Grafting of a Mixture of Substituted Phenyl Groups at a Glassy Carbon Electrode Surface

Two‐component substituted aryl groups are simultaneously grafted onto the surface of a glassy carbon electrode by electrochemical reduction of a binary mixture of two aryl diazonium salts in acetonitrile. The electrochemical deposition is achieved potentiostatically and two different mixtures with four different ratios of diazonium salts are used. The binary mixtures comprise: 1) 4‐nitrophenyl diazonium and 4‐bromophenyl diazonium cations and 2) 4‐bromophenyl diazonium and N,N‐diethylaniline diazonium cations. The chemical composition of the two component films is determined by cyclic voltammetry in an electrolyte inert for electroactive groups such as nitrophenyl and bromophenyl. X‐ray photoelectron spectroscopy is also used to evaluate the surface concentration of each grafted substituted phenyl group. The surface concentration of the substituted phenyl group for which the corresponding diazonium cation is the most easily reduced is higher than its concentration in the mixture of the deposition solution. The usefulness of binary films is also discussed.     

Coupling of two diazotized 3‐aminothieno[3,4‐c]coumarins with aromatic amines

The coupling reactions of two diazotized 3‐aminothieno[3,4‐c]coumarins were investigated. Compounds 1a , 1b both react with sodium nitrite in concentrated sulphuric acid at 0–5°C to give the diazotized intermediates 2 and 3 , the latter resulting from the acid ‐catalyzed hydrolysis of the lactonic ring of 2 . The in situ formed diazonium salts react with aromatic amines ( 4 ) to afford a series of arylazothiophenes dyes in the form of their ammonium sulfate salts. With diazotized aniline, besides the normally expected phenylazothiophene 10 from the reaction with compound 1a , the corresponding product of acid hydrolysis 11 was also isolated. In at least one of the cases, the thienyl diazonium salt 2 undergoes a Gomberg–Bachmann arylation reaction with p‐nitroaniline to give the 2‐arylthiophene 9 . The direct hydrolysis of compounds 1a , 1b by concentrated sulphuric acid and subsequent oxidative dimerization of the primary product of acid hydrolysis led to compound 12 . J. Heterocyclic Chem., (2011).     

二苯胺-4-偶氮磺酸盐及其树脂的制备和光、热分解性质

从二苯胺 4 重氮盐(DS)和3 甲氧基二苯胺 4 重氮盐(MDS)以及重氮树脂(DR)和硝基重氮树脂(NDR)与亚硫酸钠反应,在水溶液中制备了相应的二苯胺 4 偶氮磺酸盐DSS和MDSS(简称偶氮磺酸盐)及相应的重氮树脂的偶氮磺酸盐DRS和NDRS(简称偶氮磺酸盐树脂).对它们在水溶液和固相膜中的光、热反应进行了研究.结果表明偶氮磺酸盐与偶氮磺酸盐树脂有很好的感光性能,而热稳定性比相应的重氮盐和重氮树脂好很多,其中二苯胺上有硝基取代的偶氮磺酸盐树脂具有突出的热稳定性,其水溶液在70℃加热6h,其固相膜在100℃加热11天几乎观察不到分解.对偶氮磺酸盐及偶氮磺酸盐树脂的光、热分解机理作了初步分析.     

不同结构二苯胺重氮盐及重氮树脂的光,热分解

对二苯胺-4-重氮盐(DS)、邻-甲氧基二苯胺-4-重氮盐(MDS)和N-甲基-间硝基二苯胺-4-重氮盐(NDS)及它们的重氮树脂(DR,MDR,NDR)在水溶液中的光,热分解研究表明,这些重氮盐和树脂的光分解性质,即感光灵敏性差别不大,而热分解性质,即热稳定性差别很大.MDS的热稳定性最好.固相膜中3种树脂的光分解亦差别不大,但N-甲基-间硝基二苯胺-4-重氮树脂(NDR)固相膜的热稳定性出乎预料地好.从疏水性的角度对NDR固相膜突出的热稳定性作了初步解释.     

Pd-catalyzed [2+2+1] coupling of alkynes and arenes: phenol diazonium salts as mechanistic trapdoors

Alkynes and phenol diazonium salts undergo a Pd-catalyzed [2+2+1] cyclization reaction to spiro[4,5]decatetraene-7-ones. This structure was confirmed for one example by X-ray single-crystal structure analysis. The reaction is believed to proceed through oxidative addition of the phenol diazonium cation to Pd(0), subsequent insertion of two alkynes, followed by irreversible spirocyclization.     

m-Aminophenylarsonic Acid as an Analytical Form for the Photometric Determination of Phenol in Water

The azocoupling reaction of diazonium salts of o- and m-aminophenylarsonic acids with phenol was studied. On the basis of quantum-chemical calculations of the reagents, conformation analysis of resulting azo compounds, and experimental data, it was found that the meta isomer of aminophenylarsonic acid is of practical interest as an analytical reagent for the determination of phenol. The advantage of the proposed reagent is a high stability of the diazonium salt. A procedure was developed for the spectrophotometric determination of phenol in water at a level of 0.06 g/mL. The error in the determination is no higher than 5.5%.     

Mechanistic Study of a Photocatalyzed CS Bond Formation Involving Alkyl/Aryl Thiosulfate

This study presents thioether construction involving alkyl/aryl thiosulfates and diazonium salt catalyzed by visible‐light‐excited [Ru(bpy)₃Cl₂] at room temperature in 44–86 % yield. Electron paramagnetic resonance studies found that thiosulfate radical formation was promoted by K₂CO₃. Conversely, radicals generated from BnSH or BnSSBn (Bn=benzyl) were clearly suppressed, demonstrating the special property of thiosulfate in this system. Transient absorption spectra confirmed the electron‐transfer process between [Ru(bpy)₃Cl₂] and 4‐MeO‐phenyl diazonium salt, which occurred with a rate constant of 1.69×10⁹ M ^?1 s^?1. The corresponding radical trapping product was confirmed by X‐ray diffraction. The full reaction mechanism was determined together with emission quenching data. Furthermore, this system efficiently avoided the over‐oxidation of sulfide caused by H₂O in the photoexcited system containing Ru²⁺. Both aryl and heteroaryl diazonium salts with various electronic properties were investigated for synthetic compatibility. Both alkyl‐ and aryl‐substituted thiosulfates could be used as substrates. Notably, pharmaceutical derivatives afforded late‐stage sulfuration smoothly under mild conditions.     

Keteniminium‐Driven Umpolung Difunctionalization of Ynamides

A three‐component Pd‐catalyzed coupling of ynamides, aryl diazonium salts, and aryl boronic acids for the synthesis of novel triaryl‐substituted enamides is described. This transformation represents the first example of an umpolung regioselective unsymmetrical syn‐1,2‐diarylation/aryl‐olefination of ynamides. The aryl moieties of the diazonium salt (electrophile) and boronic acid (nucleophile) are explicitly incorporated in the electrophilic α‐ and nucleophilic β‐position, respectively, of the ynamide, resulting in a single isomer of the N‐bearing tetrasubstituted olefin. The scope is broad (68 examples), showing excellent functional‐group tolerance. DFT calculations substantiate the rationale of the mechanistic cycle and the regioselectivity. The chemoselectivity and synthetic potential of the enamide products were also studied.     

A Comparative Study of the Modification of Gold and Glassy Carbon Surfaces with Mixed Layers of In Situ Generated Aryl Diazonium Compounds

In situ generated aryl diazonium cations were synthesized in the electrochemical cell by reaction of the corresponding amines with NaNO₂ in aqueous HCl. This paper reports a study of the formation of mixed layers from in situ generated aryl diazonium cations. Firstly, glassy carbon (GC) and gold electrode surfaces were modified with five single in situ generated aryl diazonium salts to obtain their corresponding reductive potential followed by the modification of GC and gold surfaces with eight binary mixed layers of in situ generated aryl diazonium salts. The difference between GC and gold surfaces in terms of in situ formation of two‐component aryl diazonium salt films was compared. The behavior of the mixed layers formed from in situ generated aryl diazonium salts relative to diazonium salts that were pre‐synthesized prior to surface modification was also investigated. Cyclic voltammetry and X‐ray photoelectron spectroscopy were used to characterize the resulting modified GC and gold surfaces. It is found that for some aryl diazonium salts the potential at which reductive adsorption is achieved on gold and GC surfaces is significantly different. For the eight sets of binary mixed layers, the species with more anodic potential are more difficult to attach to the both GC and gold surfaces. The behavior of the mixed layers formed from in situ generated aryl diazonium salts and the pre‐synthesized diazonium salts is similar; which emphasizes the advantage of the in situ approach without any apparent difference in behavior to the presynthesized diazonium salts.     

Synthesis of 7‐Alkoxy/Hydroxy‐α‐methyltryptamines

Abstract

A simple method for the preparation of 7‐alkoxy/hydroxy‐α‐methyl‐DL‐tryptamines is reported. The key steps of the synthesis are the Japp–Klingemann coupling of 2‐piperidone‐3‐carboxylic acid 3 with diazonium salts 4, the Fischer‐type cyclization of hydrazones 5 to β‐carboline derivatives 6 and their hydrolysis to title compounds 8.     

Studies with functionally substituted N‐alkylazoles: The reactivity of 1‐(3,5‐dimethylpyrazol‐1‐yl)‐acetone towards electrophilic reagents

The reaction of 1‐(3,5‐dimethylpyrazol‐1‐yl)acetone 4 with aromatic diazonium salts afforded the corresponding arylhydrazones 5a,b that were converted into pyridazines 6a,b and 8 via condensation with active methylene nitriles and dimethylformamide dimethylacetal, respectively. Condensation of 4 with phenylhydrazine afforded the phenylhydrazone 10 , which could be converted into the indolylpyrazole 11 on treatment with ethanolic hydrochloric acid. Compound 4 also reacted with nitrous acid, benzyl‐idenemalononitrile to yield a variety of substituted new pyrazoles.     

Synthesis and characterization of bromo‐, arylazo‐, and heterocyclic‐fused troponoids containing a 1,3‐benzodioxole system

A facile synthesis of a series of novel bromo‐, arylazo‐, and heterocyclic fused troponoid compounds containing 1,3‐benzodioxole system is described. The 7‐bromo‐, 5,7‐dibromo‐, and 5‐arylazo‐substituted 3‐[(2E)‐3‐(1,3‐benzodioxol‐5‐yl)prop‐2‐enoyl]tropolones ( 2 , 3 , and 5 , 6 , 7 ) were obtained by direct bromination or azo‐coupling reactions of 3‐[(2E)‐3‐(1,3‐benzodioxol‐5‐yl)prop‐ 2‐enoyl]tropolone ( 1 ) with bromine, and diazonium salts of aniline derivatives, respectively. 3‐[(2E)‐3‐(1,3‐Benzodioxol‐5‐yl)prop‐2‐enoyl]‐5‐bromotropolone ( 4 ) was obtained from 3‐acetyl‐5‐bromotropolone via one‐pot aldol dehydration reaction with piperonal. Tropolones 2, 3 , and 4 were subjected to nucleophilic cyclization with bifunctional hydroxylamine hydrochloride and phenylhydrazine hydrochloride to give the corresponding isoxazolo‐ and pyrazolo‐fused tropones ( 8 , 9 , 10 , 11 , 12 , 13 ), respectively. J. Heterocyclic Chem., (2012).     

Suzuki-Miyaura cross coupling reactions with phenoldiazonium salts

The Suzuki-Miyaura coupling of phenol diazonium salts and aryl trifluoroborates yields 4-hydroxybiaryls in a protecting group-free synthesis.     

2,5‐Disubstituted Pyrazolo[4,3‐c]cinnolin‐3‐ones

Complementary strategies to 2,5‐disubstituted pyrazolo[4,3‐c ]cinnolin‐3‐ones are reported herein, providing late stage substituent introduction at either the 2‐ or the 5‐position. Treating a readily prepared 4‐thiocinnoline ester with substituted hydrazines afforded late stage access to the 2‐position, while late stage substituent introduction at the 5‐position was achieved via two different strategies: alkylation of 4‐hydrazonopyrazol‐3‐ones, followed by a ring‐closing intramolecular S_NAr tactic and direct reaction of 5‐(2‐fluorophenyl)‐2,4‐dihydro‐3H‐pyrazol‐3‐ones with aryl diazonium salts, followed by cyclization. The strategies described herein provide practical and general methods to prepare 2,5‐disubstituted pyrazolo[4,3‐c ]cinnolin‐3‐ones.     

Synthesis of some isomeric quinoxaline derivatives with 6‐azauracil cycle

By diazotization of 3‐(2‐aminophenyl)‐1,2‐dihydroquinoxaline 1c, its 3‐(4‐aminophenyl)‐isomer 2c , 3‐(2‐aminobenzyl)‐1,2‐dihydroquinoxaline‐2‐one 3c and its 3‐(4‐aminobenzyl)‐isomer 4c and by azo coupling of formed diazonium salts with ethyl cyanoacetylcarbamate, corresponding hydrazones ld‐4d were prepared. Cyclization of these compounds afforded compounds containing two heterocyclic rings with acidic N‐H groups in their molecules: 3‐[2‐(5‐cyano‐6‐azauracil‐1‐yl)‐phenyl]‐1,2‐dihydroquinoxaline‐2‐one 1e , its 4‐isomer 2e , 3‐[2‐(5‐cyano‐6‐azauracil‐1‐yl)‐benzyl]‐1,2‐dihydroquinoxaline‐2‐one 3e and its 4‐isomer 4e . The aminoderivative 1c was prepared by the reaction of N‐acetylisatine with o‐phenylenediamine and by hydrolysis of prepared N‐acetylderivative 1a . The aminoderivative 2c was prepared by the condensation of 4‐acetylaminophenylglyoxylic acid with o‐phenylenediamine and by hydrolysis of prepared N‐acetylderivative 2a . The aminoderivative 3c was prepared by the condensation of 2‐nitrophenylpyruvic acid with o‐phenylenediamine and by the reduction of the formed nitroderivative 3b and finally starting aminoderivative 4c was obtained by the condensation of o‐phenylenediamine with 4‐aminophenylpyruvic acid.     

A convenient one‐pot synthesis of 1,2‐azaphospholanium salts

A novel facile one‐pot synthesis of the 1,2‐azaphospholanes by intramolecular alkylation of 3‐halopropyl amides of tricoordinate phosphorus has been suggested. Using this method, a series of the differently N‐substituted 1,2‐azaphospholanium salts were synthesized. 3‐Aminopropylphosphine oxides were obtained by hydrolysis of the salts. A probable mechanism of the 1,2‐azaphospholanium salts formation is discussed. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:596–602, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10209     

The synthesis of 4‐amino‐3‐(2‐pyridyl)pyrazolo[5,1‐c][1,2,4]triazine and some of its derivatives

A mixture of both geometrical isomers of hydrazones 3a‐3e was obtained by the coupling reactions of pyrazole‐3‐diazonium salts 2a‐2d and benzenediazonium chloride 2e with 2‐pyridylacetonitrile 1 . Hydrazones 3a‐3d were cyclized to the corresponding 4‐amino‐3‐(2‐pyridyl)pyrazolo[5,1‐c][1,2,4]triazines 4a‐4d.     

Carboxylate–phenolate tautomerism in 5‐[(nitrophenyl)diazenyl]salicylate anions

Aryldiazenyl derivatives of salicylic acid and their salts are used as dyes. In these structures, the carboxylate groups are engaged in short contacts with the cations and in hydrogen bonds with water molecules, if present. If both O atoms of the carboxylate group take part in such interactions, the negative charge is delocalized over the two atoms. In the absence of hydrogen bonds and contacts with cations, the negative charge is localized on one of the O atoms. In the crystal structures of tetramethylammonium 2‐hydroxy‐5‐[(E)‐(4‐nitrophenyl)diazenyl]benzoate and tetramethylammonium 2‐hydroxy‐5‐[(E)‐(2‐nitrophenyl)diazenyl]benzoate, both C₄H₁₂N⁺·C₁₃H₈N₃O₅⁻, all the interactions between the cations and anions are weak, and their effect on the geometry of the anions is negligible. Under these conditions, the 2‐nitro‐substituted anion is an almost pure phenol–carboxylate tautomer, whereas in the 4‐nitro‐substituted anion, the phenolic H atom is shifted towards the carboxylate group, and thus the structure of this anion is intermediate between the phenol–carboxylate and phenolate–carboxylic acid tautomeric forms. The probable formation of such an intermediate form is supported by quantum chemical calculations. Being the characteristic feature of this form, a short distance between the phenolic and carboxylate O atoms is observed in the 4‐nitro‐substituted anion, as well as in the structures of some 3,5‐dinitrosalicylates reported in the literature.     

A Base‐Free Neutral Phase‐Transfer Reaction System

Although phase‐transfer reactions catalyzed by using quaternary ammonium salts are generally believed to require base additives, we discovered that, even without any base additives, conjugate additions of 3‐substituted oxindoles to nitroolefins proceeded smoothly in the presence of lipophilic quaternary ammonium bromide under water–organic biphasic conditions. The mechanism of this novel base‐free neutral phase‐transfer reaction system is investigated and the assumed catalytic cycle is presented together with interesting effects of water and lipophilicity of the phase‐transfer catalyst. The base‐free neutral phase‐transfer reaction system can be applied to highly enantioselective conjugate addition and aldol reactions under the influence of chiral bifunctional ammonium bromides as key catalysts. The structure of the chiral ammonium enolate intermediate is discussed based on the single‐crystal X‐ray structures of relevant ammonium salts and the importance of bifunctional design of catalyst is clearly explained in the model of intermediate.     

Synthesis of cesium selective pyridyl azocalix[n]arenes

A series of pyridylazo calix[n]arenes (n=4, 6, 8) including the first examples of mixed hetroaryl azocalix(n)arenes have been synthesized by coupling calix[n]arenes with diazonium salts derived from amino pyridines. It has been observed that the coupling reaction of diazonium salt obtained from 3-aminopyridine with calix[n]arene gives tetrakis-, hexakis- and octakis (pyridylazo)calix[n]arenes (n=4,6,8) while those derived from 4-aminopyridine give partially substituted (4-pyridylazo)calix[n]arene analogs. There is no reaction of calix(n)arenes with diazonium salts derived from 2-aminopyridine under identical conditions of experiments. The conformational analysis of synthesized compounds have been ascertained by detailed spectral measurements and single crystal X-ray analysis of 5-(3′-pyridylazo)-25,26,27,28-tetrahydroxycalix[4]arene. A rational explanation for the observed partial and exhaustive coupling reaction in the synthesis of heteroaryl azocalix(n)arenes has been suggested. Preliminary evaluation of synthesized derivatives as molecular receptors for metal ions indicates that they have good potential to function as selective ionic filters for cesium ions.