Identification of [1,3]dithiolo[4,5-d]dithiazolyl radicals by in situ EPR spectroscopy and cyclic voltammetry

The synthesis of [1,3]dithiolo[4,5-d]dithiazolium salts from readily available zinc chelate has been developed. Chlorination of 2-oxo and 2-(dicyanomethylene) (2-oxo-1,3-dithiole-4,5-diyl) diethanethioates with SO₂Cl₂ followed by condensation with Me₃SiN₃ produced 1,2,3-dithiazolium chlorides. The structure of 5-(dicyanomethylene)[1,3]dithiolo[4,5-d][1,3,2]dithiazol-1-ium tetrafluoroborate was confirmed by powder X-ray diffraction, and its chemical bonding pattern as well as charge transfer were studied within the QTAIM framework applied to the results of plane wave DFT periodic calculations. Reduction with triphenylantimony and electrochemical reduction of [1,3]dithiolo[4,5-d]dithiazolium salts by cyclic voltammetry, chronoamperometry, and microelectrolysis at a controlled potential on a platinum electrode in acetonitrile revealed the formation of [1,3]dithiolo[4,5-d]dithiazolyl radicals, which were characterized by EPR spectroscopy.     

Dinuclear rhenium(I) carbonyl complexes based on π-conjugated polypyridyl ligands with tetrathiafulvalenes: Syntheses, crystal structures, properties and DFT calculations

A series of tetrathiafulvalene-substituted 2,3-di(2-pyridyl)quinoxaline (dpq) ligands, 2-(4,5-bis(methylthio)-1,3-dithiol-2-ylidene)-6,7-di(pyridin-2-yl)- [1,3]dithiolo[4,5-g]quinoxaline (L₁), dimethyl-2-(6,7-di(pyridin-2-yl)-[1,3]dithiolo[4,5-g]quinoxalin-2-ylidene)-1,3-dithiole-4,5-dicarboxylate (L₂), and 2-(5,6-dihydro-[1,3]dithiolo[4,5-b] [1,4]dithiin-2-ylidene)-6,7-di(pyridin-2-yl)-[1,3]dithiolo[4,5-g]quinoxaline (L₃), have been prepared. Reactions of these ligands with Re(CO)₅Cl afford the corresponding dinuclear rhenium(I) carbonyl complexes, Re₂(L)(CO)₆Cl₂ (L = L₁, 5a; L = L₂, 5b; L = L₃, 5c). All new compounds are fully characterized by ¹H NMR, IR and mass spectroscopies. The crystal structures of 5a and 5b have been studied. Optimized conformations and molecular orbital diagrams of 5a−5c have been calculated with density functional theory (DFT). The spin-allowed singlet−singlet electronic transitions of all complexes have been calculated with time-dependent DFT (TDDFT), and the UV-Vis−NIR spectra are discussed based on the theoretical calculations.     

Syntheses, structures, and electrochemical properties of platinum(II) complexes containing di-tert-butylbipyridine and crown ether annelated dithiolate ligands

A series of new platinum(II) complexes containing both 4,4'-di-tert-butyl-2,2'-bipyridine (dbbpy) and the extended tetrathiafulvalenedithiolate ligands have been prepared and characterized. These complexes include [Pt(dbbpy)(C8H4S8)] (1; C8H4S82- = 2-{(4,5-ethylenedithio)-1,3-dithiol-2-ylidene}-1,3-dithiol-4,5-dithiolate), [Pt(dbbpy)(ptdt)] (2; ptdt = 2-{(4,5-cyclopentodithio)-1,3-dithiol-2-ylidene}-1,3-dithiol-4,5-dithiolate), [Pt(dbbpy)(mtdt)] (3; mtdt = 2-{(4,5-methylethylenedithio)-1,3-dithiol-2-ylidene}-1,3-dithiol-4,5-dithiolate), [Pt(dbbpy)(btdt)] (4; btdt = benzotetrathiafulvalenedithiolate), [Pt(dbbpy)(C8H6S8)] (5; C8H6S82- = 2-{4,5-bis(methylthio)-1,3-dithiol-2-ylidene}-1,3-dithiol-4,5-dithiolate), [Pt(dbbpy)(3O-C6S8)] (6; 3O-C6S82- = 2-{4,5-dithia-(3',6',9'-trioxaundecyl)-1,3-dithiol-2-ylidene}-1,3-dithiol-4,5-dithiolate), and [Pt(dbbpy)(4O-C6S8)] (7; 4O-C6S82- = 2-{4,5-dithia-(3',6',9',12'-tetraoxatetradecyl)-1,3-dithiol-2-ylidene}-1,3-dithiol-4,5-dithiolate). The crystal structures of a new ligand precursor (2-[4,5-dithia-(3',6',9',12'-tetraoxatetradecyl)-1,3-dithiol-2-ylidene]-4,5-bis(2-cyanoethylsulfanyl)-1,3-dithiole, IIIc) and complexes 5-7 have been determined by X-ray crystallography. Complexes 1-7 show intense electronic absorption bands in the UV-vis region due to the intramolecular mixed metal/ligand-to-ligand charge-transfer transition, and they display significant solvatochromic behavior. Redox properties of these compounds have been investigated by cyclic voltammetry, and complex 7 shows a significant response for Na+ ions with a large positive shift of ca. 45 mV.     

Novel heterocyclic systems based on 8-R-4,5-dihydro-4,4-dimethyl-[1,2]dithiolo[3,4-c]quinoline-1-thiones

Based on the reaction of 8-R-4,5-dihydro-4,4-dimethyl[1,2]dithiolo[3,4-c]quinoline-1-thiones with oxalyl chloride followed by the reactions of 1,3-dipolar cycloaddition and diene synthesis with participation of acetylenedicarboxylic acid dimethyl ester, we have developed approaches to synthesis of novel polycondensed heterocyclic systems: [1,2]dithiolo[3,4-c]pyrrolo[3,2,1-ij]quinoline-4,5-dione, 6-(1,3-dithiol-2-ylidene)-1,2-dioxo-5-thioxo-7H-pyrrolo[3,2,1-ij]quinoline and 4,5-dioxospiro(pyrrolo)-[3,2,1-ij]thiopyrano[2,3-c]quinoline-11,2′-[1,3]dithiole. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 610–615, April, 2006.     

Unique Thermal Structural Phase Transitions Exhibited by Unsymmetrical Organometallic Gold(III)-Dithiolene Complexes with Pentylthio and Hexylthio Groups

Unsymmetrical gold(III)-dithiolene complexes are potential candidates for molecular materials that exhibit thermal structural phase transitions. In this study, unsymmetrical ppy-gold(III) (ppy⁻=C-deprotonated-2-phenylpyridine(−)) complexes [AuC5] and [AuC6] coordinated by dithiolene ligands containing tetrathiafulvalene (TTF) skeletons with pentylthio (2-{bis(pentylthio)-1,3-dithiol-2-ylidene}-1,3-dithiol-4,5-dithiolate(2−)) and hexylthio groups (2-{bis(hexylthio)-1,3-dithiol-2-ylidene}-1,3-dithiol-4,5-dithiolate(2−)) were synthesized. Both complexes exhibited a large absorption band at approximately 508 nm, owing to intramolecular ligand-to-ligand charge transfer. One-dimensional columnar structures with head-to-tail molecular arrangements around the metal ions were constructed in the crystals. The flexible alkylthio groups were intercalated into crystalline spaces between dithiolene ligands in the columns. [AuC5] exhibits a simple phase transition at 198 °C between crystalline and isotropic phases irreversibly. The crystalline phase of [AuC6] observed at 25 °C melted at 148 °C. Another crystalline phase grew above 148 °C with a very slow crystallization rate from the liquid phase and was completely transformed into an isotropic phase at 200 °C.     

Thermal decompositions of dinitropyridyl and dinitrothienyl dithiocarbamates and t-butyl trithiocarbonates

The title compounds on heating cyclized to yield 7-nitro-1,3-dithiolo[4,5-c]pyridin-2-one (III), 6-nitro-1,3-dithiolo[2,3-c]pyridin-2-one (VIIa), 6-nitrothieno[2,3-d]-1,3-dithiol-2-one (XIVa) and 6-nitrothteno[2,3-d]-1,3-dithiole-2-thione (XIVb).     

A one-pot synthesis and 1,3-dipolar cycloaddition of [1,2]dithiolo[4,3-b]indole-3(4H)-thiones

Treatment of N-substituted 2-methyl-1H-indoles 1 with S₂Cl₂ and DABCO in chloroform gave the corresponding [1,2]dithiolo[4,3-b]indole-3(4H)-thiones 5 by the addition of triethylamine in high yield. 1,2-Dithiole-3-thiones 5 underwent cycloaddition with one or two DMAD equivalents to afford either 2-(3-thioxo-1,3-dihydro-2H-indol-2-ylidene)-1,3-dithioles 10 or fused 4,5-dihydrothiopyrano[3,2-b]indoles 9.     

Synthesis of the antiepileptic (R)-Stiripentol by a combination of lipase catalyzed resolution and alkene metathesis

The enantiopure (ee >99%) antiepileptic (R)-(+)-Stiripentol has been stereoselectively synthesized via cross metathesis of 5-vinylbenzo[d][1,3]dioxole 1 and (R)-(+)-4,4-dimethylpent-1-en-3-ol (R)-(+)-2. A novel one-pot two-step pathway for the synthesis of 5-vinylbenzo[d][1,3]dioxole 1 starting from 3,4-dihydroxycinnamic acid has been introduced. A lipase catalyzed kinetic resolution access to enantiopure (R)-(+)-4,4-dimethylpent-1-en-3-ol (R)-(+)-2 (ee >99%) has also been developed.     

A (pi-extended tetrathiafulvalene)-fluorene conjugate. Unusual electrochemistry and charge transfer properties: the first observation of a covalent D(2+)-sigma-A(.-) redox state(1)

The synthesis of novel electrochemically amphoteric TTFAQ-sigma-A compounds (TTFAQ = 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene, sigma = saturated spacer, A = polynitrofluorene acceptor) is reported. Their solution redox behavior is characterized by three single-electron reduction and one two-electron oxidation waves. Electrochemical quasireversibility of the TTFAQ(2+) state and a low E(ox) - E(red) gap ( approximately 0.25 V) for 3-(9-dicyanomethylene-4,5,7-trinitrofluorene-2-sulfonyl)-propionic acid 2-[10-(4,5-dimethyl-[1,3]dithiol-2-ylidene)-9,10-dihydroanthracen-9-ylidene]-5-methyl-[1,3]dithiol-4-ylmethyl ester (10) has enabled the electrochemical generation of the hitherto unknown transient D(2+)-sigma-A(.-) state as observed in cyclic voltammetry and time-resolved spectroelectrochemistry. The ground state of compound 10 was shown to be ionic in the solid but is essentially neutral in solution (according to electron paramagnetic resonance). The X-ray structure of an intermolecular 1:2 complex between 2-[2,7-bis(2-hydroxyethoxy)-9,10-bis(4,5-dimethyl-[1,3]dithiol-2-ylidene)-9,10-dihydroanthracene and 2,5,7-trinitro-4-bromo-9-dicyanomethylenefluorene, 14.(17)(2), reveals, for the first time, full electron transfer in a fluorene charge-transfer complex.     

Transition metal complexes based on thiophene-dithiolene ligands

The chemistry of transition metal dithiolene complexes based on thiophene-dithiolene ligands (TD) is reviewed, from the ligand synthesis and complex preparation to the molecular structure and solid state physical properties of different compounds based on them. The ligands considered are based mainly either on simple thiophene-dithiolates (α-tpdt = 2,3-thiophenedithiolate, dtpdt = 4,5-dihydro-2,3-thiophenedithiolate, and tpdt = 3,4-thiophenedithiolate), or in more extended and delocalised dithiolate ligands (α-tdt = 3-({5-[(2-cyanoethyl)thio]-2-thieno[2,3-d][1,3]dithiol-2-ylidene-1,3-dithiol-4-yl}thio)propanenitrile and dtdt = 3-{5-[(2-cyanoethyl)thio]-2-(5,6-dihydrothieno[2,3-d][1,3]dithiol-2-ylidene-1,3-dithiol-4-yl)thio}propanenitrile) that besides the thiophenic ring also incorporates a fused TTF moiety. Dithiolene complexes based on ligands containing appended thiophenic units will also be briefly considered. The structural variability of these complexes that in addition to the usual square planar coordination geometry, M(TD)₂, can also present dimeric, [M(TD)₂]₂, or cluster structures such as [Cu₄(TD)₃] and [Ni₄(TD)₆], is addressed. The role of the thiophene group and its ability to enhance electronic delocalisation from the metal dithiolene core throughout the ligand and to establish solid state networks of S?S interactions is discussed. The importance of these complexes as useful building blocks to prepare molecular materials with very interesting magnetic and transport properties, ranging from metamagnets to Single Component Molecular Metals, is illustrated by different compounds based on them.     

Fused pyrimidine systems: XIII. Synthesis and some transformations of 1,3-thiazolo(thiazino)-fused pyrido[3,4-d]pyrimidines

2-[Allyl(propargyl)sulfanyl]pyrido[3,4-d]pyrimidin-4-ones at heating in polyphosphoric acid undergo an intramolecular cyclization with the formation of pyrido[4,3-e]thiazolo-[3,2-a]pyrimidin-5-ones of angular structure. Under similar conditions the cyclization of 2-(cinnamylsulfanyl)pyrido[3,4-d]-pyrimidin-4-one results in a linear pyrido[3′,4′:4,5]pyrimido-[2,1-b][1,3]thiazin-6-one. The iodocyclization of the same substrates affords the corresponding 9-(iodomethyl)(iodomethylidene)pyrido[4,3-e][1,3]thiazolo-[3,2-a]pyrimidin-5-ones and 3-iodopyrido[3′,4′:4,5]pyrimido[2,1-b][1,3]thiazin-6-one of angular structure. 9-(Iodomethyl)-8,9-dihydro-5H-pyrido[4,3-e][1,3]thiazolo[3,2-a]pyrimidin-5-one treated with sodium azide gave 9-(azidomethyl) derivative whose cyclization with substituted alkynes in the presence of copper compounds provided pyrido [4,3-e][1,3]thiazolo[3,2-a]pyrimidinylmethyltriazoles.     

Selective synthesis of bis[1,2]dithiolo[1,4]thiazines from 4-isopropylamino-5-chloro-1,2-dithiole-3-ones

Reaction of 4-isopropylamino-5-chloro-1,2-dithiole-3-ones 3 and S₂Cl₂ in acetonitrile gave selectively 3-oxo-bis[1,2]dithiolo[1,4]thiazine-5-thiones 1 by the addition of triethylamine and bis[1,2]dithiolo[1,4]thiazine-3,5-diones 5 under the action of formic acid. 3,5-Diones 5 were also obtained by intramolecular cyclization of N,N-bis(5-chloro-3-oxo[1,2]dithiol-4-yl)amines 6 with S₂Cl₂ in the presence of Et₃N.     

Synthesis of oxoindolin-3-ylidene-1,3-dithioles

An efficient and one-pot synthesis of 2-(2-oxoindolin-3-ylidene)-1,3-dithiole-4,5-dicarboxylates by a three-component condensation reaction of isatins, carbon disulfide and dialkyl acetylendicarboxylates in the presence of Bu₃P is reported. Reaction of carbon disulfide and dialkyl acetylene dicarboxylates with acenaphthylene-1,2-dione, ninhydrine and pyrimidine-tetraone resulted in the formation of 2-(2-oxoacenaphthylen-1(2H)-ylidene)-1,3-dithiole-4,5-dicarboxylates, 2-(1,3-dioxo-1H-inden-2(3H)-ylidene)-1,3-dithiole-4,5-dicarboxylates and 2-(2,4,6-trioxotetrahydropyrimidin-5(6H)-ylidene)-1,3-dithiole-4,5-dicarboxylates, respectively, in the same conditions.     

Synthesis of new condensed nitrogen heterocyclic systems

A cotarnine alkaloid-based synthesis was developed for new heptacyclic condensed diisoquinolines via the double intramolecular pseudosalt bis[1,3]dioxolo[4,5-g;4′,5′-g′][1,3,4]oxadiazolo[2,3-a;5,4-a′]diisoquinoline 6. Substitution of the central O atom in 6 by C, S, or N nucleophiles afforded the first representatives of the new ring systems bis[1,3]dioxolo[4,5-g:4,5-g′]pyrazolo[3,2-a:5,1-a′]diisoquinoline (7a-d), bis[1,3]dioxolo[4,5-g:4,5-g′][1,3,4]thiadiazolo[2,3-a:5,4-a′]diisoquinoline (8), and bis[1,3]dioxolo[4,5-g:4,5-g′][1,2,4]triazolo[3,2-a:5,1-a′]diisoquinoline (9a-d) under simple reaction conditions.     

Electrophilic heterocyclization of 6-alken(yn)ylsulfanyl-pyrazolo[3,4-<Emphasis Type="Italic">d</Emphasis>]pyrimidin-4(5<Emphasis Type="Italic">H</Emphasis>)-ones

6-Allylsulfanyl-1-arylpyrazolo[3,4-d]pyrimidin-4(5H)-ones react with iodine and sulfuric acid to give angular pyrazolothiazolopyrimidine derivatives. The reaction of 6-(prop-2-yn-1-ylsulfanyl)-1-(4-tolyl)-pyrazolo[3,4-d]pyrimidin-4(5H)-one with sulfuric acid gives angularly fused pyrazolo[4,3-e][1,3]thiazolo-[3,2-a]pyrimidin-4-one, whereas in the reaction with sodium methoxide linearly fused pyrazolo[3,4-d][1,3]-thiazolo[3,2-a]pyrimidin-4-one was formed. Linearly fused pyrazolo[3′,4′:4,5]pyrimido[2,1-b][1,3]thiazole derivatives were also obtained by reaction of 1-aryl-6-(3-phenylprop-2-en-1-ylsulfanyl)pyrazolo[3,4-d]pyrimidin-4(5H)-ones with sulfuric acid.     

Hetero-diels–alder reaction of 5-ylidene-4-sulfanylidene-1,3-thiazolidin-2-ones with <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>′-bis(methoxycarbonyl)-1,4-benzoquinone diimine

Hetero-Diels–Alder reaction of 5-(propan-2-ylidene)-4-sulfanylidene-1,3-thiazolidin-2-one with N,N′-bis(methoxycarbonyl)-1,4-benzoquinone diimine in boiling toluene afforded 87% of dimethyl 9,9-dimethyl-2-oxo-8a,9-dihydro-2H-thiochromeno[2,3-d][1,3]thiazole-5,8(3H,4aH)-diylidenedicarbamate. Analogous reactions of 5-benzylidene-, 5-{[4-(dimethylamino)phenyl]methylidene}-, and 5-[(2-hydroxyphenyl)-methylidene]-4-sulfanylidene-1,3-thiazolidin-2-ones led to the formation of the corresponding dimethyl 9-aryl-2-oxo-3,9-dihydro-2H-thiochromeno[2,3-d][1,3]thiazole-5,8-diyldicarbamates in 64–82% yield.     

Five-membered 2,3-dioxo heterocycles: CI. Reaction of 3-aroylpyrrolo[2,1-c][1,4]benzoxazine-1,2,4-triones with arylhydrazines. Crystal and molecular structure of substituted 2-hydrazonopyrrolo[2,1-c][1,4]benzoxazine

A new direction of nucleophilic attack was revealed in the reactions of 3-aroylpyrrolo[2,1-c][1,4]-benzoxazine-1,2,4-triones with o-tolylhydrazine and 2-hydrazinylbenzoic acid hydrochloride, which afforded the corresponding hydrazones at the C²=O carbonyl group, substituted 2-(2-o-tolylhydrazono)pyrrolo[2,1-c]-[1,4]benzoxazine-1,4(2H)-diones and pyrrolo[2,1-c][1,4]benzoxazin-2(4H)-ylidenehydrazinylbenzoic acids. The structure of (Z)-2-{2-[3-benzoyl-1,4-dioxo-1H-pyrrolo[2,1-c][1,4]benzoxazin-2(4H)-ylidene]hydrazinyl}-benzoic acid was determined by X-ray analysis.     

One-pot three component isocyanide-based reaction: Synthesis of novel tetracyclic fused furo[2′,3′:4,5]pyrimido[2,1-b][1,3]benzothiazole

A rapid, efficient and benign protocol has been developed for the construction of potentially biologically active furo[2′,3′:4,5]pyrimido[2,1-b][1,3]benzothiazole derivatives as major products along with (3E)-3-[(alkylamino)methylene]-2H-pyrimido[2,1-b][1,3]benzothiazole-2,4(3H)-dione derivatives as minor products using a one-pot, multi-component reaction of isocyanides, aromatic aldehydes and 2-hydroxy-4H-pyrimido[2,1-b][1,3]benzothiazol-4-one. The significant features of this protocol are the readily available and low-cost starting materials, short reaction time, mild reaction conditions, high yield of products and avoidance of toxic solvents and catalysts. Structures of compounds 4b and 5a were confirmed from single crystal X-ray studies.     

Syntheses,Electrochemical Behaviors,Spectral Properties and DFT Calculations of Two 1,3-Dithiole Derivatives

Two new 1,3-dithiole derivatives, 4,4＇-{9-[4,5-bis（methylthio）-1,3-dithiol-2-ylidene]-9H-fluorene-2,7- diyl} dipyridine（2a） and 3,3＇-{9-[4,5-bis（methylthio）-1,3-dithiol-2-ylidene]-9H-fluorene-2,7-diyl} dipyridine（2b） were synthesized and characterized by Fourier transform infrared（FTIR）, 1H NMR, 13C NMR and mass spectroscopies. The crystal structure of compound 2b was also studied. The optimized conformations and molecular orbital diagrams of compounds 2a and 2b were illustrated via density functional theory（DFT）. By the time-dependent DFT（TD-DFT） method, electronic absorption spectra of compounds 2a and 2b were predicted and the results achieved were in good agreement with the experimental data. The formation of the cationic radical during the electrochemical oxidation process was also proposed.     

trans-Aconitic acid-based hetero-Diels-Alder reaction in the synthesis of thiopyrano[2,3-d][1,3]thiazole derivatives

The hetero-Diels-Alder reaction of 5-arylideneisorhodanines with trans-aconitic acid proceeds as a regio- and diastereoselective process with spontaneous decarboxylation of the [4+2]-adduct to furnish thiopyrano[2,3-d][1,3]thiazole (2) and chromeno[4′,3′:4,5]thiopyrano[2,3-d]thiazole (3) derivatives analogously to the use of itaconic acid as a dienophile. Conversely, the one-pot, three-component reaction of 5-arylideneisorhodanines, trans-aconitic acid and anilines proceeded without decarboxylation, leading to novel rel-(5′R,6′R,7′R)-5′-carboxy-7′-aryl-1-aryl-3′,7′-dihydro-2H,2′H,5H-spiro[pyrrolidin-3,6′-thiopyrano[2,3-d]thiazol]-2,2′,5-triones 4. Interestingly, the use of trans-aconitic acid trimethyl ester led to the opposite regioselectivity, yielding rel-(5R,6S,7S)-5-methyloxycarbonylmethyl-2-oxo-7-aryl-3,5,6,7-tetrahydro-2H-thiopyrano[2,3-d]thiazol-5,6-dicarboxylates 5. Selected compounds were examined for trypanocide activity against the bloodstream forms of Trypanosoma brucei where compound 4e showed the highest activity (IC₅₀ = 6.74 μM).