Arenium cation as the key intermediate of the electrosynthesis of <Emphasis Type="Italic">N</Emphasis>-(2,5-dimethoxyphenyl)azoles. A new approach to the synthesis of <Emphasis Type="Italic">N</Emphasis>-(dimethoxyphenyl)azoles

Data on the effect of the acid-base properties of the medium on the yield and composition of the products of N-dimethoxyphenylation of azoles (pyrazole, triazole, their substituted derivatives, and tetrazole) upon galvanostatic electrolysis of azole—1,4-dimethoxybenzene mixtures in nucleophilic (MeOH) and neutral (MeCN) media were considered and the trends of this process were discussed. The generation of arenium cations (1,4-dimethoxy-1-azolylbenzenium in MeCN and 1,1,4-trimethoxybenzenium in MeOH) as the key intermediates of electrosynthesis of N-(dimethoxyphenyl)azoles, was proved experimentally. A new approach to the synthesis of N-(dimethoxyphenyl)azoles through electrosynthesis of 1,1,4,4-tetramethoxycyclohexa-2,5-diene by electrooxidation of 1,4-dimethoxybenzene in MeOH as the first step and the reaction of this quinone diketal with azoles as the second step was suggested. The efficiency of this route to N-(dimethoxyphenyl)azoles is comparable with the efficiency of the purely electrochemical one-step process. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2101–2109, November, 2007.     

Reactions of some arenes and pyrazoles in MeCN under conditions of undivided-cell electrolysis

As exemplified for the first time by pyrazole and its 4-nitro and 3,5-dimethyl derivatives, N-arylation of pyrazoles can be performed under conditions of undivided-cell amperostatic electrolysis (Pt electrodes, MeCN) of systems containing the pyrazolate anion and (or) pyrazole, arene (benzene, 1,4-dimethoxybenzene, or xylene), and a supporting electrolyte. In the case of electrolysis involving 1,4-dimethoxybenzene as arene, N-arylation followed simultaneously three routes to form an ortho-substitution product (1,4-dimethoxy-2-(pyrazol-1-yl)benzene), an ipso-substitution product (4-methoxy-1-(pyrazol-1-yl)benzene), and an ipso-bisaddition product (1,4-dimethoxy-1,4-di(pyrazol-1-yl)cyclohexa-2,5-diene) in a total current yield of up to 50%. The acid-base properties of the pyrazoles under study affect the ratio of the N-arylation products and govern the required composition of the starting reaction mixture. In the case of a stronger base, such as 3,5-dimethylpyrazole, N-arylation with 1,4-dimethoxybenzene occurred even in the pyrazole—arene—tetraalkylammonium perchlorate system, whereas N-arylation of 4-nitropyrazole (a weaker base) proceeded only in the presence of the pyrazolate anion or another base, viz., sym-collidine. Oxidation of arene to the radical cation is the key anodic reaction. Not only the pyrazolate anion, but also highly basic pyrazole or a solvate complex of weakly basic pyrazole with collidine can serve as a nucleophilic partner in subsequent transformations of these radical cations.     

N-Dimethoxyphenylation of highly basic pyrazoles during undivided electrolysis

The reactions of pyrazole, 3,5-dimethylpyrazole, and its 4-nitro derivatives with 1,4-dimethoxybenzene during undivided amperostatic electrolysis in MeCN (CH₂Cl₂) were studied. The basicity of the medium, which depends on the solvent nature, the nature and concentration of pyrazole and the acid-base properties of additives, and the amount of electricity passed determine the yield and relative content of the target products, viz., 1,4-dimethoxy-2-(pyrazol-1-yl)benzenes (1) and 1,4-dimethoxy-1,4-di(pyrazol-1-yl)cyclohexa-2,5-dienes (2). The process occurs mainly through the interaction of the nonionized solvato complex of pyrazole with the 1,4-dimethoxybenzene radical cation and affords radical intermediates structurally similar to compounds 1 and 2. The key stage of the process determining the 1 : 2 ratio is the rearrangement of the intermediately produced 1,4-dimethoxy-1-(pyrazol-1-yl)arenonium cation to the 1-(pyrazol-1-yl)-2,5-dimethoxyarenonium cation.     

Oxidative trifluoroacetamidation of (1<Emphasis Type="Italic">E</Emphasis>,3<Emphasis Type="Italic">E</Emphasis>)-1,4-diphenylbuta-1,3-diene and 1,1,4,4-tetraphenylbuta-1,3-diene

Reactions of trifluoroacetamide with (1E,3E)-1,4-diphenylbuta-1,3-diene and 1,1,4,4-tetraphenylbuta-1,3-diene in the oxidative system t-BuOCl–NaI have been studied. The reaction with (1E,3E)-1,4-diphenylbuta-1,3-diene afforded three products, N,N′-(phenylmethylene)bis(trifluoroacetamide), 3-chloro-4-iodo- 2,5-diphenyl-1-(trifluoroacetyl)pyrrolidine, and trifluoro-N-[(3E)-2-hydroxy-1,4-diphenylbut-3-en-1-yl]acetamide, with a high overall yield. 1,1,4,4-Tetraphenylbuta-1,3-diene failed to react with trifluoroacetamide.     

Electrosynthesis of N-Arylazoles by Electrolyzing a Mixture of Azole and 1,4-Dimethoxybenzene in a Diaphragmless Cell

An analysis is performed and data are compared on the electrosynthesis of N-arylazoles and regularities of this process in conditions of a diaphragmless galvanostatic electrolysis (Pt, MeCN, Bu₄NClO₄) of a mixture of 1,4-dimethoxybenzene (DMB) with azoles (pyrazole, triazole, their derivatives, tetrazole). Electrolysis of an azole/DMB mixture leads to the formation of products of an ortho-substitution—1,4-dimethoxy-2-(azolyl-1)benzenes—and, simultaneously, hydrolytically unstable products of an ipso-bis-attachment—1,4-dimethoxy-1,4-di-(azolyl-1)cyclohexa-2,5-dienes. The overall yield of these compounds increases upon adding a base (collidine) or an acid (AcOH) into the initial mixture, and the basicity of initial azoles substantially affects the electrosynthesis results. New notions on the nature of nucleophilic species interacting with radical cation of DMB are considered. The species in question are complexes of azoles with one another or with collidine generated at the expense of the hydrogen bond, rather than azolate ions. Furthermore, the cathodic process is largely connected not with the generation of azolate ions (as a result of the reduction of initial azoles) but with the deprotonation of onium compounds (BH⁺)—products of the interaction of azoles or collidine with protons. The mechanism of electrosynthesis of N-arylazoles is discussed. The key stages of the synthesis are the attack of a nucleophile on the ipso- and, possibly, ortho-positions of the benzene ring of radical cation of DMB, as well as the rearrangement of the intermediate cation of 1,4-dimethoxy-1-(azolyl-1)arenonium into the cation of 1-(azolyl-1)-2,5-dimethoxyarenonium, which affects both the yield and ratio of final products of the reaction mixture.     

Cross-coupling of E,E-1,4-diiodobuta-1,3-diene with nucleophiles catalyzed by Pd or Ni complexes: a new route to functionalized dienes

E,E-1,4-Diiodobuta-1,3-diene can enter into cross-coupling reactions with carbon- or other element-centered nucleophiles in the presence of Pd or Ni complexes as catalysts. Convenient procedures were developed for the stereoselective synthesis of E,E-1,4-dialkenylbuta-1,3-dienes, dienyl-1,4-bisphosphonates, E,E-1,4-bis(diphenylphosphino)buta-1,3-diene, E,E-1,4-diphenylbuta-1,3-diene, and E,E-1,4-bis(thiophenyl)buta-1,3-diene.     

Synthesis of π-conjugated poly(arylene)s by polycondensation of 1,4-bis(3-methylpyridin-2-yl)benzene and aryl dibromides through regiospecific C-H functionalization process

On the basis of the Ru-catalyzed regiospecific direct double arylation of benzene rings possessing 3-methylpyridin-2-yl substituents to produce 1-aryl-2-(3-methylpyridin-2-yl)benzene derivatives, the synthesis of poly(p-phenylene) derivatives having 2,5-bis(3-methylpyridin-2-yl) substituents is described. The reaction of 1,4-bis(3-methylpyridin-2-yl)benzene with bromobenzene (2 equiv) was carried out in the presence of [RuCl₂(η⁶-C₆H₆)]₂ (5 mol %) in 1-methyl-2-pyrrolidone at 120°C for 24 h to produce 1,4-bis(3-methylpyridin-2-yl)-2,5-diphenylbenzene in 99% yield as a sole product. Neither 2,6-diphenylated nor further phenylated products was produced under the examined conditions. This regiospecific double arylation process was then applied to the synthesis of π-conjugated polymers by use of aryl dibromides such as 1,4-dibromobenzene, 2,7-dibromo-9,9-dihexylfluorene, and 2,5-dibromothiophene. For example, a polymer was obtained in 73% yield by using 1,4-dibromobenzene, whose M_n and M_w/M_n were estimated to be 3300 and 1.51, respectively. The bathochromic shift of the ultraviolet (UV)–visible absorption spectrum with respect to that of the model compound, 1,4-bis(3-methylpyridin-2-yl)-2,5-diphenylbenzene, indicated the extension of the π-conjugation. The blue fluorescence was also observed for the polymer upon the UV irradiation. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2771–2777     

Reaction sites of <Emphasis Type="Italic">N,N′</Emphasis>-substituted <Emphasis Type="Italic">p</Emphasis>-phenylenediamine antioxidants

The geometries of N,N′-diphenylbenzene-1,4-diamine (DPPD), N-phenyl-N′-(1-phenylethyl)benzene-1,4-diamine (SPPD), N-(4-methylpentan-2-yl)-N′-phenylbenzene-1,4-diamine (6PPD), N-propan-2-yl-N′-phenylbenzene-1,4-diamine (IPPD), N-(2-methoxybenzyl)-N′-phenylbenzene-1,4-diamine (MBPPD), and N-phenyl-N′-(2-phenylpropan-2-yl)benzene-1,4-diamine (CPPD) as well as of their dehydrogenation products were optimized by the semiempirical AM1 method. The results support the idea of stable N_B=C_X structures formation during the consecutive dehydrogenation of SPPD, 6PPD, IPPD, and MBPPD antioxidants. The biradicals formed during the second step of dehydrogenation of substituted phenylenediamines might be important for their antioxidant effectiveness. Dedicated to Professor Vladimír Kvasnička, DrSc., in honour of his 65th birthday     

Über den Mechanismus der Cope-Umlagerung

On the Mechanism of the Cope Rearrangement The rates of the Cope rearrangement of 2,5-dicyano-3-methyl-hexa-1, 5-diene ( 12 ), (E)- and (Z)-2, 5-dicyano-hepta-1,5-diene ((E)- and (Z)- 14 ) as well as of 2, 5-dimethoxycarbonyl-3-methyl-hexa-1,5-diene ( 13 ) and (E)- and (Z)-2,5-dimethoxycarbonyl-hepta-1,5-diene ((E)- and (Z)- 15 ) were measured in decane solution in the temperature range of 50 to 150° (see Tables 5 and 8 to 12). A detailed English summary of this work is given in [1 b].     

Electrochemical transformations of monooxa- and dioxabicycloalkenes and-bicycloalkanes

Electrolysis of 2-oxa- and 2,5-dioxabicyclo[n.4.0]alk-1(6)0enes (n=4, 10) under conditions of direct undivided anodic oxidation in methanol results in their electrochemical mono-and dimethoxylation; electrolysis of the corresponding 2-oxa-and 2,5-dioxabicycloalkanes involves electrochemical cleavage of the bridging carbon—carbon bonds followed by electrooxidative transformation into methyl ω-(2-methoxytetrahydrofuryl)-, ω-(dimethoxy-methyl)-, and ω-(1,3-dioxolan-2-yl)alkanoates. For preliminary communication, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2115–2122, November, 1999.     

A new method for the synthesis of [1,4]diazepino[6,5-b]indole derivatives

Reactions of 3-[(N-aryl-N-chloroacetyl)amino]-2-formylindoles with substituted anilines gave 1,4-diaryl-2-oxo-1,2,3,6-tetrahydro[1,4]diazepino[6,5-b]indol-4-ium chlorides and those with 4-aminopyridine yielded 4-amino-1-(1-aryl-2-oxo-2,5-dihydro-1H-pyrido[3,2-b]indol-3-yl)pyridinium chlorides. Reduction of 1,2,3,6-tetrahydrodiazepinoindol-4-ium chlorides afforded the corresponding hexahydro derivatives. An alternative synthesis of 1-(4-nitrophenyl)-3-oxo-4-phenyl-1,2,3,4,5,6-hexahydro[1,4]diazepino[6,5-b]indole from 3-[N-(4-nitrophenyl)amino]-2-[(phenylimino)methyl]indole was developed. The method involves the following sequence of transformations: reduction, chloroacetylation, and intramolecular alkylation. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2193–2199, December, 2006.     

Chiral Alkoxy Side Chains from (-)-Amino Acids in Mediating Asymmetric Synthesis of Tricarbonyl(cyclohexadienyl)iron Complexes

The asymmetric induction in the complexation reaction of (S)-1-methyl-2-(5-methyl-cyclohexa-1,4-dienylmethyloxy)-pyrrolidine 5 and (S)-2-(2-N,N-dimethylamino-1-propanoxy)-5-methylcyclohexa-1,4-diene 6 having heteroatom adjacent the stereogenic center has been investigated. The diastereoselectivity was determined directly from the diastereotopic peaks in the ¹H NMR or by chemical correlation with 9 . The conversion of η-1,4-complexes 7a and 8a to 9 proceeded with high retention of configuration while that of the η-2,5-Fe(CO)₃ complexes 7b and 8b undergoes considerable racemization.     

Spectral-luminescence properties of some 2,5-dihydroxy-1,4-di(azol-2-yl)benzenes

The influence of the type of azole fragments and substituents on the spectral-luminescence properties of a series of 2,5-dihydroxy-1,4-di(azol-2-yl)benzenes, possessing an anomalously high Stokes shift, was investigated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 242–245, February, 1993.     

Diazepines II. A new synthesis of 4h-pyrrolo[ 1,2-α] -[1,41] benzodiazepine

A convenient synthesis of a 4H-pyrroIo[1,2-α][1,4 ]benzodiazepine is described. 2,5-Di-methoxy-2-melhyl-5-phthalimidomethyltetrahydrofuran ( 3 ) was prepared starting from 2-methyl-5-phthalimidomelhylfuran ( 1 ). The condensation of 2-amino-5-chlorobenzophcnone with 3 to give 5-chloro-2-(2-methyl-5-phthalimidomethylpyrro]-1-yl)benzophenone ( 4 ), the treatment of which with hydrazine hydrate afforded 8-chloro-1-methyl-4H-pyrrolo[1,2-α] [1,4]benzodiazepine ( 5 ).     

Synthesis and tuberculocidic activity of some 4-arylaminomethylene-3-methyl-1-(pyrimidin-2-yl)pyrazol-5(4H)-ones

4-Arylaminomethylene-3-methyl-1-(6-methyl-4-oxo-1,4-dihydropyrimidin-2-yl)pyrazol-5(4H)-ones were synthesized by a three-component reaction between the 6-methyl-2-(3-methyl-5-oxo-2,5-dihydropyrazol-1-yl)pyrimidin-4(1H)-one, triethoxymethane, and an aromatic amine. These compounds were found to exist as aminomethyleneketones regardless of the electronic effects of substituents in the aromatic fragments. The resulting compounds showed pronounced tuberculocidic activity.     

N-Arylation of azoles with low basicity by 1,4-dimethoxybenzene during undivided electrolysis

The reactions of 1,4-dimethoxybenzene with 4-nitropyrazole, 3,4-dinitro-5-methylpyrazole, 1,2,4-triazole, 3-nitro-1,2,4-triazole, and tetrazole were studied during undivided amperostatic electrolysis on a Pt electrode in MeCN, CH₂Cl₂, and MeOH. The main reaction products were 2-azolyl-1,4-dimethoxybenzenes and (or) 1,4-diazolyl-1,4-dimethoxycyclohexa-2,5-dienes. In all cases except 1,2,4-triazole, N-arylation occurs only in the presence of the Alk₄N⁺ salts of azoles or 2,4,6-trimethylpyridine as a base. The mechanism of the reactions is discussed.     

Synthesis of benzoquinone derivatives containing benzotriazole fragments

2,3,5,6-Tetrakis(1H-benzotriazol-1-yl)-1,4-benzoquinone was synthesized in 85% yield by reaction of 2,3,5,6-tetrachloro-1,4-benzoquinone with 1H-benzotriazole in pyridine at room temperature. Treatment of 2,3,5,6-tetrakis(1H-benzotriazol-1-yl)-1,4-benzoquinone with piperidine, ω-amino acids, and aromatic amines gave the corresponding 2,5-diamino-3,6-bis(1H-benzotriazol-1-yl)-1,4-benzoquinones.     

Structures and photochromic properties of fulgides based on naphtho[1,2-<Emphasis Type="Italic">b</Emphasis>]furan and benzo[<Emphasis Type="Italic">g</Emphasis>]indole

The novel heterocyclic fulgides, i.e. 3-isopropylidene-4-{1-[5-methoxy-1-(4-methoxy-phenyl)-2-methyl-1H-benzo[g]indol-3-yl]ethylidene}dihydrofuran-2,5-dione and 3-isopropylidene-4-[1-(1-benzyl-5-methoxy-2-methyl-1H-benzo[g]indol-3-yl)ethylidene]dihydrofuran-2,5-dione, were prepared and isolated as E-isomers. Photochromism, E-configuration, and high resistance to photocoloration—photobleaching of solutions of these fulgides as well as 3-isopropylidene-4-[1-(5-methoxy-2-methylnaphtho[1,2-b]furan-3-yl)ethylidene]dihydro-furan-2,5-dione and 3-isopropylidene-4-[1-(5-methoxy-2-methyl-1-phenyl-1H-benzo[g]indol-3-yl)ethylidene]dihydrofuran-2,5-dione synthesized previously were shown by X-ray diffraction analysis, ¹H NMR spectroscopy and electronic absorption spectroscopy. The novel fulgides show fluorescence and high thermal stability of photogenerated cyclic form. Repeated photo-coloration—photobleaching is accompanied by reversible photoinduced E—Z isomerization. Benzo[g]indolyl fulgides are characterized by the longer wavelength absorption of both original (E) and photoisomeric cyclic (C) forms as compared to naphthofuran fulgide.     

Aromatic glyoxalimines in criss-cross cycloaddition reactions

Aromatic 1,4-diazabuta-1,3-dienes in glacial acetic acid with thiocyanates produce via criss-cross cycloaddition reactions the corresponding perhydroimidazo[4,5-d]imidazole-2,5-dithiones. When a mixture of thiocyanate and cyanate in a proper ratio was reacted together, nonsymmetrical 5-thioxo-perhydroimidazo[4,5-d]imidazole-2-ones were isolated. With cyanates substituted aromatic 1,4-diazabuta-1,3-dienes afforded product of acetic acid addition to primary formed 1,3-dipole intermediate 5-(4-substituted phenylamino)-3-(4-substituted phenyl)-2-oxoimidazolidin-4-yl acetate.     

Synthesis of novel 3-(1,3-thiazol-2-yl)-7,8-dihydroquinoline-2,5(1H,6H)-diones

An efficient method for the synthesis of novel 3-(1,3-thiazol-2-yl)-7,8-dihydroquinoline-2,5(1H,6H)-diones from various 2-dimethylaminomethylidenecyclohexane-1,3-diones, (1,3-thiazol-2-yl)acetonitriles, and dimethylformamide dimethyl acetal was developed. These transformations proceeded through intermediate 2-[2-(4-aryl-1,3-thiazol-2-yl)-2-cyanoethenyl]-3-oxocyclohex-1-en-1-olates. They were isolated as piperidinium salts and used in further heterocyclization reactions with aromatic amines, giving novel 1-aryl-3-(1,3-thiazol-2-yl)-7,8-dihydroquinoline-2,5(1H,6H)-diones. These compounds were also obtained by preparative three-step “one pot” synthesis under controlled microwave irradiation. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 412–417, February, 2008.