Spectroscopic,Theoretical, and Electrochemical Studies of 1,2-Dithiins

The lowest oxidation potentials for 1,2-dithiins are in the range of 0.67-0.96 V in acetonitrile and 0.81-1.04 V in dichloromethane. These oxidation potentials are less anodic than expected based on the ionization potentials of 1,2-dithiin determined by photoelectron spectroscopy. Theoretical calculations suggest that the reason for this difference is a change in optimized geometry between 1,2-dithiin and its oxidized species.     

1,2-Dichalcogenins: Simple Syntheses of 1,2-Diselenins, 1,2-Dithiins,and 2-Selenathiin

Ring opening of titanacyclopentadienes 1 with (SCN)₂ or (SeCN)₂ followed by bis(thiocyanate) or bis(selenocyanate) cyclization affords 1,2-dithiin ( 2 a ) or 1,2-diselenin ( 2 b ), respectively. Compound 1 gives 2 a directly on reaction with S₂Cl₂. Unsubstituted 1,2-diselenin is prepared by reaction of PhCH₂SeNa with 1,4-bis(trimethylsilyl)-1,3-butadiyne followed by reductive cleavage of the benzyl group and oxidation. The unsubstituted 2-selenathiin is prepared in an analogous manner, but from a mixture of PhCH₂SeNa and PhCH₂SNa.     

Ab initio molecular orbital study of energies and conformers of 3,4-dihydro-1,2-dithiin, 3,6-dihydro-1,2-dithiin, 4H-1,3-dithiin,and 2,3-dihydro-1,4-dithiin

Optimized geometries and energies for 3,4-dihydro-1,2-dithiin ( 1 ), 3,6-dihydro-1,2-dithiin ( 2 ), 4H-1,3-dithiin ( 3 ), and 2,3-dihydro-1,4-dithiin ( 4 ) were calculated using ab initio 6-31G* and MP2/6-31G*//6-31G* methods. At the MP2/6-31G*//6-31G* level, the half-chair conformer of 4 is more stable than those of 1 , 2 , and 3 by 2.5, 3.5, and 3.6 kcal/mol, respectively. The half-chair conformers of 1 , 2 , 3 , and 4 are 2.9, 7.1, 2.0, and 5.6 kcal/mol, respectively, more stable than their boat conformers. The calculated half-chair structures of 1 – 4 are compared with the calculated chair conformer of cyclohexane and the half-chair structures for cyclohexene, 3,4-dihydro-1,2-dioxin ( 5 ), 3,6-dihydro-1,2-dioxin ( 6 ), 4H-1,3-dioxin ( 7 ), and 2,3-dihydro-1,4-dioxin ( 8 ). © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1064–1071, 1998     

Synthesis, structure, and reactivity of novel 3,4-diphosphacyclobutenes bearing silyl groups

[reaction: see text] Copper-mediated homocoupling of sterically hindered 2-(2,4,6-tri-tert-butylphenyl)-1-trialkylsilyl-2-phosphaethenyllithiums afforded 1,2-bis(trialkylsilyl)-3,4-diphosphacyclobutenes (1,2-dihydrodiphosphetenes) through a formal electrocyclic [2+2] cyclization in the P=C-C=P skeleton as well as 2-trimethylsilyl-1,4-diphosphabuta-1,3-diene. Reduction of 1,2-bis(trimethylsilyl)-3,4-diphosphacyclobutenes followed by quenching with electrophiles afforded ring-opened products, (E)-1,2-bis(phosphino)-1,2-bis(trimethylsilyl)ethene and (Z)-2,3-bis(trimethylsilyl)-1,4-diphosphabut-1-ene. The structures of the ring-opened products indicated E/Z isomerization around the C=C bond after P-P bond cleavage of 5, and the isomerization of the P-C=C skeleton. Ring opening of 1,2-bis(trimethylsilyl)-3,4-diphosphacyclobutenes affording (E,E)- and (Z,Z)-1,4-diphosphabuta-1,3-dienes was observed upon desilylation.     

Iron-Semiquinone, Semiquinone-Semiquinone, and Iron-Iron Magnetic Exchange in Monomeric and Dimeric Ferric Complexes Containing the 3,6-Di-tert-butyl-1,2-semiquinonate Ligand

Fe(3,6-DBSQ)(3) has been prepared by reacting 3,6-di-tert-butyl-1,2-benzoquinone with Fe(CO)(5). The complex has been characterized structurally [orthorhombic, Pbca, a = 18.277(5) ?, b = 11.634(3) ?, c = 39.903(10) ?, V = 8485(4) ?(3), Z = 8, R = 0.063], electrochemically, and magnetically. Ligand-based redox couples are observed in electrochemical experiments that consist of reversible or quasireversible Cat/SQ steps at negative potentials and irreversible SQ/BQ oxidations at positive potentials. Magnetic measurements show temperature dependence that arises from antiferromagnetic exchange. Data have been fit to an expression that includes the effects of both Fe-SQ and SQ-SQ exchange with the result that J(SQ-SQ) is larger in magnitude than J(Fe-SQ). In methanol, the complex undergoes solvolysis to form [Fe(3,6-DBSQ)(2)(&mgr;-OMe)](2). Structural characterization [triclinic, P&onemacr;, a = 11.441(2) ?, b = 11.514(2) ?, c = 14.552(2) ?, alpha = 67.86(1) degrees, beta = 70.51(1) degrees, gamma = 72.79(1) degrees, V = 1641.8(5) ?(3), Z = 1, R = 0.048] has shown that the molecule is a centrosymmetric dimer with no close intermolecular contacts. The temperature dependence of magnetic measurements has been fit to a model consisting of two interacting S = (3)/(2) centers that arise from strong Fe-SQ exchange with J(Fe-Fe) = -22.4 cm(-1).     

Polyfunctional macroheterocycles

The reaction of 1-[1,2-bis(carbomethoxy)ethyl]aziridine with ethane-1,2-dithiol leads to 1.8-bis[1,2-bis(carbomethoxy)ethylamino]-3,6-dithiaoctane. Condensation with phthalic and terephthalic acid dichloride gives 9,10-benzo-8, 11-dioxo-7,12-bis[1,2-bis(carbomethoxy)ethyl]-1,4-dithia-7,12-diazacyclotetradec-9-ene and 9,12-benzo-8,13-dioxo-7,14-bis[1,2-bis(carbomethoxy)ethyl]-1,4-dithia-7,14-diazacyclohexadeca-9,12-diene, respectively, while condensation with formaldehyde gives 7,9,18,20-tetrakis[1,2-bis(carbomethoxy)ethyl]-1,4,12,15-tetrathia-7,9,18.29-tetraazacyclodocosane. The corresponding disulfone is formed in the oxidation of 9,10-benzo-8,11-dioxo-7,12-bis[1,2-bis(carbomethoxy) ethyl]-1,4-dithia-7,12-diazacyclotetradec-9-ene with 30% hydrogen peroxide.See [1] for Communication 1.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1563–1565, November, 1988.     

Heteroatomic derivatives of aziridine. 14. Reactions of 1-(carbomethoxyethyl)-, 1-[1,2-bis(carbethoxy)ethyl]-, and 1-[1,2-bis(carbomethoxy)vinyl]aziridine with thiols, 1,2-ethanedithiol,and thiolcarboxylic acids

The reactions of 1-(carbomethoxyethyl)-, 1-[1,2-bis(carbethoxy)-ethyl]-, and 1-[1,2-bis(carbomethoxy)vinyl]aziridine with thiols and thiolcarboxylic acids produce the corresponding sulfides and esters of S-substituted N-(2-mercaptoethyl) amino acids. The reaction of 1-[1,2-bis(carbethoxy)ethyl]aziridine with 1,2-ethane-dithiol results in the formation of {1,8-bis[1,2-bis(carbethoxy)-ethyl]amino}-3,6-dithiaoctane. Cyclization of the latter by condensation with phthaloyl chloride gives 9,10-benzo-8,11-dioxo-1,4-dithia-7,12-bis[1,2-bis(carbethoxy)ethyl]-7,12-diazacyclotetradec-9-ene.For report 13 see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1340–1342, October, 1984.     

Molecular structures and electronic transitions of 3,6-diphenyl-1,2-dithiin and its radical cation: a spectroelectrochemical and DFT study

One-electron oxidation of 3,6-diphenyl-1,2-dithiin yields the corresponding radical cation. The product is stable at low temperatures and can be distinguished by a triplet EPR signal. Cyclic voltammetric, UV-vis spectroelectrochemical, and DFT studies were performed to elucidate its molecular structure and electronic properties. Time-dependent DFT calculations reproduce appreciably well the UV-vis spectral changes observed during the oxidation. The results reveal a moderately twisted structure of the 1,2-dithiin heterocycle in the radical cation.     

General synthesis of extended fused oligothiophenes consisting of an even number of thiophene rings

The intramolecular double cyclization of bis(3-bromo-2-thienyl)acetylenes though a lithium-halogen exchange reaction with tBuLi followed by treatment with elemental sulfur produces two thiophene-fused thieno[3,2-c](1,2-dithiin)s. The subsequent dechalcogenation from the 1,2-dithiins with copper nanopowder affords tetrathienoacenes. On the basis of this two-step procedure, a series of trialkylsilyl-terminated, fused oligothiophenes, including hexathienoacene (a six thiophene-fused system) and octathienoacene (an eight thiophene-fused system), were synthesized. In the UV/Vis absorption and fluorescence spectra of the fused oligothiophenes, the absorption and emission maxima shift to longer wavelengths, as the pi-conjugation length increases. Their maximum wavenumbers have linear relationships with the reciprocal number of thiophene rings consisting of the pi-conjugated frameworks. In the cyclic voltammograms, all the compounds show reversible oxidation waves, the first oxidation potential of which shifts to less positive as the conjugation length increases. Among them, the octathienoacene also shows a reversible second oxidation process. Indeed, its chemical oxidation with an excess amount of NO(+)SbF(6) (-) produces the dication as a golden crystal. The crystal structures of the neutral octathienoacene and its dication were determined by X-ray crystallography. While in the neutral state, the octathienoacene has a benzenoid structure with a large bond alternation of about 0.04 A, its dication has a quinoid structure in which two cationic charges are mainly localized on the terminal rings.     

Nucleophilic substitution with amines: dihydro-1,2,4,5-tetrazines are more useful precursors than 1,2,4,5-tetrazines

A one step synthesis of (di)alkylamino-substituted 1,2,4,5-tetrazines direct from 3,6-disubstituted-1,2-dihydro-1,2,4,5-tetrazine precursors is described. A comparative study revealed that the described method not only avoids the up-to-now required oxidation step but also lower reaction times and/or temperatures compared to usual protocols. The efficiency of the reaction was highlighted by a practical synthesis of 3,6-bis(methylamino)-1,2,4,5-tetrazine using aqueous methylamine. Other primary and secondary amines were also found to give disubstitution products when reacted with 3,6-bis(methylsulfanyl)-1,2,4,5-dihydrotetrazine.     

Crystal engineering using anilic acids and dipyridyl compounds through a new supramolecular synthon

The anilic acids, 2,5-dihydroxy-1,4-benzoquinone (1a), 2,5-dibromo-3,6-dihydroxy-1,4-benzoquinone (bromanilic acid; 1b), 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (chloranilic acid; 1c), and 2,5-dicyano-3,6-dihydroxy-1,4-benzoquinone (cyananilic acid; 1d), were cocrystallized with rigid organic ligands containing two pyridine rings, 2,4-bipyridine (2a), 4,4'-bipyridine (2b), 1,2-bis(2-pyridyl)ethylene (3a), 1,2-bis(4-pyridyl)ethylene (3b), 2,2'-dipyridylacetylene (4a), 3,3'-dipyridylacetylene (4b), and 4,4'-dipyridylacetylene (4c). Fourteen complexes 5-18 were obtained as single crystals, and their crystal structures were successfully determined by X-ray analysis. All complexes except those with 2a are 1:1 and are composed of an infinite linear or zigzag tape structure, the formation of which is ascribed to intermolecular O-H...N, N(+)-H...O, or N(+)-H...O(-) hydrogen bonds or a combination of these between the anilic acids and the dipyridyl compounds. In the complexes 5 and 6, no infinite tape structure is observed although the molecular units connected by a similar hydrogen-bonding pattern are formed. For the 1:1 complexes, we have found two types of stacking arrangements, segregated stacks (7, 9, 12-15, 18) and alternated ones (8, 10, 11, 16, 17). In the complexes of 1c with the series of dipyridylacetylenes 4 (14, 15, 17), the neutral, dication, and monocaction states are formed depending on the nitrogen positions, which can be attributed to the different basicity of the pyridyl groups.     

Synthesis of 6-(arylthio)- and 6-[(arylmethyl)thio] -1,2,4,5-tetrazin-3-amines and n-phenyl- and n-(phenylmethyl)-1,2,4,5-tetrazine-3,6-diamines as potential antimalarial agents

Alkylation of tetrahydro-1,2,4,5-tetrazine-3,6-dithione with iodomethane and 1,2-dichloro-4-(chloromethyl)benzene, respectively (Scheme 1, 4 ) followed by oxidation afforded 3,6-bis(methylthio)- and 3,6-bis[[(3,4-dichlorophenyl)methyl]thio]-1,2,4,5-tetrazines ( 6, 15 ). The reaction of 15 with amines provided the 6-[(arylmethyl)thio]-1,2,4,5-tetrazin-3-amines ( 16) while sequential displacement of both methylthio groups in 6 afforded the tetrazine-diamines 8 and 10 . Hydrolysis of N,N-dimethyl-6-(methylthio)-1,2,4,5-tetrazin-3-amine ( 11 ) with potassium hydroxide afforded the tetrazin-3-ol ( 12 ) which was chlorinated and then treated with 4-chlorobenzenethiol to provide 13 . The target 6-substituted-1,2,4,5-tetrazin-3-amines displayed negligible antimalarial activity.     

Konformationsanalyse von 1,4:3,6-bis(Thioanhydro)-D-idit Derivaten

Analysis of the ¹H NMR spectra of 1,4:3,6-bis (thioanhydro)-D -iditol derivatives ( 1a to 1c ) led to the prediction of the dominant conformations. The configuration and conformation of the symmetric ( 3 ) and asymmetric ( 4 ) disulphoxides as well as that of the disulphone ( 5 ), obtained by oxidation of the 2,5-di-O-acetyl-1,4:3,6-bis(thioanhydro)-D -iditol ( 1b ) was also determined.     

TRANSITION METAL COMPLEXES OF OLIGOTHIOETHER QUINOLYLOXY TERMINATED PODANDS: PART 2. CRYSTAL AND MOLECULAR STRUCTURE OF (1,8-BIS(QUINOLYLOXY)-3,6-DITHIAOCTANE)-COPPER(II) DIPERCHLORATE TRIHYDRATE

Abstract

The synthesis of the new ligand 1,8-bis(quinolyloxy)-3,6-dithiaoctane (1) and the corresponding Cu(II), Cu(I) and Co(II) complexes is reported. The crystal and molecular structure of the copper(II) complex, [Cu(1)](ClO₄)₂.3H₂O, has been determined by X-ray diffraction methods. The complex crystallizes in the orthorhombic space group Fddd, with cell data Z = 16, a = 20.326(2), b = 20.879(3) and c = 28.308(4)Å. The structure consists of discrete [Cu(1)]^?2+ cations separated by (structurally disordered) perchlorate anions and three lattice water molecules per cation. The coordination geometry about the copper atom is pseudo-octahedral with the quinoline nitrogen and thioether sulfur atoms at the equatorial positions and the ether oxygen atoms at the axial positions. ¹H NMR line-broadening experiments indicate that electron-transfer self-exchange reactions between the copper(I) and copper(II) complexes of (1) is immeasurably slow on the NMR time-scale. The coordination chemistry of (1) is compared with its oxygen analogue, 1,8-bis(quinolyloxy)-3,6-dioxaoctane.     

Copper-catalyzed anti-hydrophosphination reaction of 1-alkynylphosphines with diphenylphosphine providing (Z)-1,2-diphosphino-1-alkenes

Hydrophosphination of 1-alkynylphosphines with diphenylphosphine proceeds in an anti fashion under copper catalysis, providing an easy and efficient access to a variety of (Z)-1,2-diphosphino-1-alkenes and their sulfides. The reaction is highly chemoselective and can be performed even in an aqueous medium. The reaction is reliable enough to realize a gram-scale synthesis of (Z)-1,2-diphosphino-1-alkene. Radical reduction of the diphosphine disulfides with tris(trimethylsilyl)silane yields the parent trivalent diphosphines without suffering from the isomerization of the olefinic geometry. Enantioselective hydrogenation of (Z)-3,3-dimethyl-1,2-bis(diphenylthiophosphinyl)-1-butene followed by desulfidation leads to a new chiral bidentate phosphine ligand.     

An improved synthesis of 3,6-diamino-1,2,4,5-tetrazine. II. From triaminoguanidine and 2,4-pentanedione

A new synthesis for the title compound that gives an 80% overall yield was developed. Treatment of triaminoguanidine monohydrochloride ( 1 ) with 2,4-pentanedione ( 2 ) gave 3,6-bis(3,5-dimethylpyrazol-1-yl)-1,2-dihydro-1,2,4,5-tetrazine ( 3 ) in 80–85% yield. Oxidation of 3 with nitric oxide or nitrogen dioxide to 3,6-bis(3,5-dimethyylpyrazol-1-yl)-1,2,4,5-tetrazine ( 4 ) followed by ammonolysis of 4 gave 3,6-diamino-1,2,4,5-tetrazine ( 5 ) in guantitatively yields.     

IR spectroscopy and single crystal X-ray diffraction study of 1,2-bis(2-aminophenoxy)-ethane, 1,5-bis(2-aminophenoxy)-3-oxapentane,and 1,8-bis(2-aminophenoxy)-3,6-dioxaoctane

Vibrational spectra of 1,2-bis(2-aminophenoxy)-ethane, 1,5-bis(2-aminophenoxy)-3-oxapentane, and 1,8-bis(2-aminophenoxy)-3,6-dioxaoctane–podands, different in the length of oxyethylene fragments, are measured and their single crystal X-ray diffraction analysis is performed. It is demonstrated that the strength of intermolecular hydrogen bonds (IMHB) with the participation of NH groups increases with the elongation of the oxyethylene spacer. According to the XRD data for 1,2-bis(2-aminophenoxy)-ethane, the weakest hydrogen bonds are characteristic. From the IR spectra, important intermolecular hydrogen bonds are typical of 1,8-bis(2-aminophenoxy)-3,6-dioxaoctane having the longest oxyethylene fragment.     

Studies of the inner reorganization energies of the cation radicals of 1,4-bis(dimethylamino)benzene, 9,10-bis(dimethylamino)anthracene, and 3,6-bis(dimethylamino)durene by photoelectron spectroscopy and reinterpretation of the mechanism of the electrochemical oxidation of the parent diamines

The inner reorganization energy of the cation radical of 1,4-bis(dimethylamino)benzene, 1, has been determined to be 0.72 +/- 0.02 eV by means of gas-phase photoelectron spectroscopy (PES). PES studies of 9,10-bis(dimethylamino)anthracene, 2, and 3,6-bis(dimethylamino)durene, 3, demonstrate that their reorganization energies are smaller than that of 1. The effect of lowering the inner reorganization energy on the rate constant for an electrochemical electron-transfer reaction is to increase the electron-transfer rate constant, k(s). However, voltammetric studies of the two-electron oxidation of 2 and 3 indicate that the values of k(s) for each step are smaller than those for 1, in contradistinction to the measured differences in reorganization energies. The voltammetric studies of 2 and 3 were reinterpreted according to a mechanism in which each step of oxidation was written as a two-step process, electron transfer with a small inner reorganization energy plus a chemical step of structural change. The agreement of simulations according to this mechanism with the experimental data was excellent. The new reaction scheme eliminated some suspicious features previously obtained with an analysis where electron transfer and structural change were considered to be concerted. In particular, all electron-transfer coefficients (alpha) were close to one-half, whereas the earlier treatment produced values of alpha much larger or smaller than one-half.     

Préparation de dithiényl-2-éthène-1,2, de dithiényl-2-pyrimidine-2,4 et de dithiényl-2-pyridazine-3,6

The condensation of 2-thienylmagnesium bromide with (Z)-1,2-dichloroethene 2,4-dichloropyrimidne, 3,6-dichloropyridazine and with a transition metal catalyst is described. The yields of these reactions are very good; 1,2-bis(2-thienyl)ethene and two new heterocyclic compounds 2,4-bis92-thientyl)pyrimidine and 3,6-bis(2-thienyl)pyridazine were obtained in one step from commercial products.     

Synthesis, structure, and electrochemical properties of biferrocenes annulated with 1,2-dithiin and 1,2-dithiin 1,1-dioxides

2,2″-Bis(N,N-dimethylaminosulfonyl)-1,1″-biferrocene (6), a precursor of biferrocenes annulated with 1,2-dithiin and 1,2-dithiin 1,1-dioxides, was prepared by a sequence of selective ortho-lithiation and dimerization reaction from N,N-dimethylaminosulfonylferrocene. New biferrocenes annulated with 1,2-dithiin (1) and 1,2-dithiin 1,1-dioxides (2) and (3) were successfully synthesized in satisfactory yields by the reaction of compound 6 with lithium aluminum hydride followed by treatment with chlorotrimethylsilane. The electrochemical properties of the biferrocenes (1)-(3) were furnished by voltammetric studies.