Catalytic hydroformamination of 2,5-dimethoxy-2,5-dihydrofurans

N-Substituted 3- and 4-formylpyrroles have been obtained by hydroformamination of 2,5-dimethoxy-2,5-dihydrofurans in the presence of HRh(CO)(PPh₃)₃.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1837–1840, August, 1990.     

The Reaction of 2,5-Dimethoxy-2,5-Dihydrofuran with Dichloroketene

2,5-Dimethoxy-2,5-dihydrofuran (DDF) reacts with dichloroketene to give 7,9-dimethoxy-3,3,5,5-tetrachloro-8-oxabicyclo[4,3,0]-noan-2,4-dione (I), and methyl chloro-(2,5-dihydro-5-methoxy-2-furanylidene) acetate (II). The reactions of 2,5-dihydrofuran and 2,5-dimethoxy-tetrahydrofuran with dichloroketene were also-studied for comparison. Compound II was derived from the insertion of a molecule of dichloroketene into the C-O bond of DDF with subsequent dehydrochlorination. Compound I resulted from the cycloaddition of two molecules of dichloroketene to the C=C bond of DDF. A mechanism involving a 1,5-dipolar intermediate is proposed to account for this novel reaction.     

Use of palladium-mediated allylic substitution reactions in the synthesis of 2,5-disubstituted-2,5-dihydrofurans

2,5-Disubstituted-2,5-dihydrofurans were synthesised in both one- and two-pot reactions starting from 2,5-diacetoxy-2,5-dihydrofuran. These palladium-mediated allylic substitution reactions were useful in preparing symmetrical or unsymmetrical products by employing the same nucleophile twice or two different nucleophiles, respectively.     

Syntheses and properties of donor-acceptor-type 2,5-diarylthiophene and 2,5-diarylthiazole

[structure: see text] Syntheses of differently substituted 2,5-diarylthiophenes and 2,5-diarylthiazoles are carried out with the palladium-catalyzed C-H substitution reaction using AgF as an activator. Remarkably strong photoluminescence is observed in 2,5-diarylthiophene. Differences between the physical properties of liquid crystalline characteristics and cyclic voltammograms of thiophene and thiazole are also studied.     

2,5-二甲氧基乙苯的合成方法及改进

以对苯二酚为起始原料，经醚化、傅瑞德尔-克拉夫慈反应酰化、乌尔夫-黄鸣龙反应还原制得2,5-二甲氧基乙苯，总收率达66．8％。     

Mechanism and selectivity of radical alkylation of 3,4-Dichloro-2,5-dihydrofuran-2,5-dione

The mechanism of radical alkylation of 3,4-dichloro-2,5-dihydrofuran-2,5-dione with cyclohexane and 2,3-dimethylbutane follows an addition-elimination pattern with reversible formation of alkyl radicals. The proposed kinetic scheme takes into account the possibility for isomerization of primary 2,3-dimethylbutane radicals into tertiary and is consistent with the experimental data. The regioselectivity of the process is linearly related to the concentration of hydrogen chloride, so that the rate constant for the addition of primary 2,3-dimethylbutane radical to 3,4-dichloro-2,5-dihydrofuran-2,5-dione may be estimated. Effective procedures for the synthesis of 3-chloro-4-(2,3-dimethylbut-2-yl)-, 3-chloro-4-cyclohexyl-, and 3,4-dicyclohexyl-2,5-dihydrofuran-2,5-diones have been proposed.     

Synthesis of 2,5-diethynyl substituted oxepins from trans-1,4-diethynylcyclohexa-2,5-diene-1,4-diols

Reaction of trans-1,4-bis(trimethylsilylethynyl)cyclohexa-2,5-diene-1,4-diol with n-BuLi followed by methanesulfonyl chloride resulted in the formation of a dark red solid, which was identified as 2,5-bis(trimethylsilylethynyl)oxepin. Deprotection of the silyl groups resulted in the formation of 2,5-diethynyloxepin, a red, shock sensitive solid. Reaction of a differentially substituted cyclohexa-2,5-diene-1,4-diol gave a mixture of 2,5-diethynyl substituted oxepins.     

Electrochemical Synthesis of 2,5-Dichloroaniline

A procedure was proposed for electrochemical reduction of 2,5-dichloronitrobenzene to 2,5-dichloroaniline in aqueous-ethanolic solution of sulfuric acid. The procedure for preparing 2,5-dichloroanilinium sulfate was optimized. The influence exerted by the cathode material, nature and amount of the organic solvent, sulfuric acid concentration, and electrolysis temperature on the yield and quality of the target product was discussed.     

Synthesis and Chemistry of 2,5-Dimethylene-2,5-Dihydrofuran

2,5-Dimethylene-2,5-dihydrofuran (3), generated flash pyrolitically, underwent di- and trimerization reactions to give cyclic dimer and trimer. Compound 3 was trapped with methanol, ethanol, bromine, acetic acid, thiophenol and oxygen. Results from trapping experiments suggest that the diradical form of 3 is involved.     

Facile synthesis of macrocyclic tetrazoles by regioselective cycloalkylation of bistetrazoles with 2,5-dimethylhexane-2,5-diol in perchloric acid

Alkylation of 1,5-bis(tetrazol-5-yl)-3-oxapentane with 2,5-dimethylhexane-2,5-diol in 65% aqueous perchloric acid was found to proceed selectively on the N2 atoms of both tetrazole rings generating a 15-membered macrocycle with tetrazol-2,5-diyl moieties incorporated (yield ca. 80%). Under analogous alkylation conditions 1,5-bis(1-methyltetrazol-5-yl)-3-oxapentane undergoes quaternization resulting in a macrocyclic tetrazolium perchlorate containing two 1-methyltetrazolium-3,5-diyl units linked by 3-oxapentane-1,5-diyl and 2,5-dimethylhexane-2,5-diyl bridges. Crystal structures of the macrocyclic compounds obtained, determined by single crystal X-ray analysis, are described.     

Synthesis and catalytic oxidation of 2,5-dimethylpyrazine

The classical method for obtaining 2,5-dimethylpyrazine by cyclization of amino-acetone has been improved by use of ammonium persulfate in place of mercuric chloride in the stage of catalytic oxidation of 2,5-dimethyldihydropyrazine. Catalytic vapor phase oxidation of 2,5-dimethylpyrazine gave 5-methylpyrazine-2-aldehyde and pyrazine-2,5-dialdehyde.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1124–1126, August, 1986.     

Synthesis and characterization of polymers derived from 2,5-dimethoxy-terephthaldehyde and 2,5-dimethoxy-terephthalic acid

Polyamides were synthesized from 2,5-dimethoxyterephthaloyl dichloride and diamines. Also, polyimines and polyaldoles were prepared from 2,5-dimethoxy-terephthaldehyde with diamines and ketones. The polymers were characterized by elemental analysis and infrared and NMR spectroscopy. Their intrinsic viscosity, glass transition temperature, and thermaldecomposition temperatures were determined.     

2,5-Dimethylcyclopentene-2-one-1

Conclusions 2,5-Dimethylcyclopentene-2-one-1 (V) was synthesized by bromination-dehydrobromination of 2,5-dimethyleyclopentanone.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2211–2213, December, 1966.     

Synthesis and characteristics of the mass spectra of 2,5-dimercapto-2,5-dimethyltetrahydrothiophene

2,5-Dimercapto-2,5-dimethyltetrahyrothiophene was synthesized by the reaction of 1-iodopropan-2-one with hydrogen sulfide in an ether solution of hydrogen chloride at-70°C. Its structure was established by mass spectrometry, ¹H and ¹³C NMR spectroscopy. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, 216–219, February, 2007.     

Structural diversity in the first metal complexes of 2,5-dicarboxamidopyrroles and 2,5-dicarbothioamidopyrroles

Metal complexes of 2,5-dicarboxamidopyrroles and 2,5-dicarbothioamidopyrroles have been structurally characterised for the first time, complementing the significant amount of work that has been reported for the analogous pyridine ligands. N,N'-Bis(3,5-dinitrophenyl)-3,4-diphenyl-1H-pyrrole-2,5-dicarboxamide forms octahedral bis(tridentate) complexes with cobalt(iii) and nickel(ii), where the ligands are bound to the metal centres through deprotonated pyrrole and amide N atoms. N,N'-Dibutyl-3,4-diphenyl-1H-pyrrole-2,5-dicarboxthioamide and N,N'-diphenyl-3,4-diphenyl-1H-pyrrole-2,5-dicarboxthioamide also form bis(tridentate) cobalt complexes but are only deprotonated at the pyrrole N atom, the remainder of the coordination sphere comprising the thioamide S atoms. The dibutyl derivative was isolated as a Co(ii) complex, whereas the diphenyl system deposited a Co(iii) complex. In contrast, N,N'-dibutyl-3,4-dichloro-1H-pyrrole-2,5-dicarboxamide was found to act as a bidentate ligand, in an octahedral cobalt(ii) complex comprising of two bidentate pyrrole ligands, and two aqua ligands. Synthesis of N,N-bis(pyridin-2-ylmethyl)-3,4-diphenyl-1H-pyrrole-2,5-carboxamide gave a pyrrole ligand with increased denticity. Reaction with cobalt(ii) chloride resulted in the isolation of a dinuclear helicate complex. The ligand was found to have undergone addition of a methoxy group to one of the linking methylene carbons, presumably as a result of the oxidative addition of solvent methanol.     

Acid-mediated cycloalkylation of C-aminoazoles with 2,5-dimethylhexane-2,5-diol

Alkylation of 5-aminotetrazole with 2,5-dimethylhexane-2,5-diol in perchloric acid was found to proceed on an endocyclic nitrogen atom as well as on the amino group, giving 5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-4H-tetrazolo[1,5-a][1,3]diazepine. Under analogous conditions, 3-amino-1,2,4-triazole undergoes cycloalkylation of the neighboring N1 and N2 atoms of the heterocycle resulting in 1-amino-5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-[1,2,4]triazolo[1,2-a]pyridazinium perchlorate. The crystal structures of the products were determined by single crystal X-ray analysis.     

2,5-Dimethoxy-2,5-dihydrofurans in 1,3-dipolar cycloaddition reactions

Itis shown that 2,5-dimethoxy-2,5-dihydrofurans enter into 1,3-dipolar cycloaddition with benzonitrile N-oxides and with diphenylnitrilimines to form derivatives of 1,3-dimethoxy-6-phenyl-1,3,3a,6a-tetrahydrofuro[3,4-d]isoxazole and 1,3-dimethoxy-4,6-diphenyl-1,3,3a,-6a-tetrahydrofuro[3,4-d]pyrazole, respectively.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 150–151, February, 1971.     

Facile one-step synthesis of 2,5-diketopiperazines

We report a one-step protocol for the general synthesis of 2,5-diketopiperazines from an Fmoc-protected amino acid and an amino acid ester. The application of the method is highlighted by rapid and efficient preparation of various 2,5-diketopiperazines.     

One-pot oxidation and bromination of 3,4-diaryl-2,5-dihydrothiophenes using Br2: synthesis and application of 3,4-diaryl-2,5-dibromothiophenes

A class of 3,4-diaryl-2,5-dibromothiophenes (1b-5b) was synthesized by a one-pot reaction of 3,4-diaryl-2,5-dihydrothiophenes with Br2 reagent in excellent yield (83-92%). It was found that Br2 performed a double function (oxidation and bromination) during the conversion of 3,4-diaryl-2,5-dihydrothiophenes to 3,4-diaryl-2,5-dibromothiophenes. The application of 3,4-diaryl-2,5-dibromothiophenes used as building blocks was also investigated. Employing 3,4-diphenyl-2,5-dibromothiophene (1b) as a template, a class of 2,3,4,5-tetraarylthiophenes was prepared by the Suzuki coupling reaction. This provided a new and simple approach to the preparation of 2,3,4,5-tetraarylthiophenes.     

气相色谱法分析2，5-二叔丁基氢醌

摘要：由氢醌与叔丁醇反应制得抗氧化剂2,5-二叔丁基氢醌。采用OV-101弹性石英毛细管柱和火焰离子检测器,用气相色谱归一化法测定了2,5-二叔丁基氢醌,并分析了其中所含氢醌、叔丁基氢醌、叔丁基对苯醌和2,5-二叔丁基对苯醌等杂质。