A one-pot synthesis of 1,4-dithiins and 1,4-benzodithiins from ketones using the recyclable reagent 1,1′-(ethane-1,2-diyl)dipyridinium bistribromide (EDPBT)

A novel access to 1,4-dithiins and 1,4-benzodithiins from the corresponding ketones in one-pot using the recyclable reagent, 1,1′-(ethane-1,2-diyl)dipyridinium bistribromide (EDPBT) is described. This method is mild, simple, environmentally benign and is applied successfully for the ring expansion of 1,3-dithiolane to 1,4-dithiins and the ring expansion associated with aromatisation of cyclic ketones with or without double bonds in the ring. The main feature of this method is that EDPBT acts as a promoter in the formation of 1,3-dithiolane and as a reagent in the ring expansion step. The spent reagent can be recovered, regenerated and reused.     

Ring expansion reactions of 1,3-dithiolans and 1,3-dithians. A new synthesis of dihydro-1,4-dithiins and dihydro-1,4-dithiepins

A mild and convenient method for ring expansion of 1,3-dithiolans and 1,3-dithians to dihydro-1,4-dithiins and dihydro-1,4-dithiepins, respectively, using phenyl selenenyl chloride in methylene chloride is described. A mechanism involving sulphenyl chloride derivatives as intermediates is proposed.     

Facile synthesis of substituted dihydro-1,4-dithiins and -1,4-dithiepins from α-oxo ketene cyclic dithioacetals

A novel and facile synthesis of substituted 2,3-dihydro-1,4-dithiins and 6,7-dihydro-5H-1,4-dithiepins based on the reactions of α-bromo/hydroxy ketones with α-oxo ketene cyclic dithioacetals has been developed. A general mechanism for the reactions is proposed.     

Syntheses of polycyclic-1,4-dithiines and related heterocycles

Reactions of dihalogenoquinones or dihalogenoquinoxalines with thioamides gave the corresponding 1,4-dithiines in high yields. Many of polycyclic 1,4-dithiin derivatives can be synthesized by the reactions of dihalogenoheterocycles with thioamides, and they are useful as pigments and functional materials for electro-optical applications. Some of heteroaromatic-1,4-dithiins formed an intermolecular charge-transfer (CT) complex with a π-acceptor such as TCNQ, and they are useful as π-donors for CT complex.     

Synthesis of 1,4-dithiins from pentathiepins

Fused aromatic and heterocyclic 1,2,3,4,5-pentathiepins react with triphenylphosphine and alkynes bearing electron-withdrawing groups to give the corresponding 1,4-dithiins in high yields. Unsymmetrical alkynes add regioselectively to afford products in agreement with the electron distribution in a proposed reaction intermediate. A mechanism for these reactions is proposed.     

Chemistry of Ethanediyl S,S-Acetals. VII. A Stereoselective Synthesis of Allylic Alcohols with cis-Configurated Double Bond

A new high yielding coupling reaction of C-2 monosubstituted 5,6-dihydro-1,4-dithiins with aldehydes is reported. In this way allylic alcohols having the cis-substituted double bond tied up by a sulfur-containing ring can be readily prepared. Subsequent stereoselective sulfur removal then affords allylic alcohols with cis-configurated double bond.     

Reactions of silica chloride (SiO(2)Cl)/DMSO, a heterogeneous system for the facile regeneration of carbonyl compounds from thioacetals and ring-expansion annelation of cyclic thioacetals

Silica chloride (SiO(2)Cl)/DMSO, as a heterogeneous system, has been efficiently used for deprotection of thioacetals into aldehydes in dry CH(2)Cl(2) at room temperature. Thioketals without enolizable hydrogens adjacent to a sulfur atom are converted easily to the corresponding ketones in high yields under similar reaction conditions. However, thioketals with enolizable methyl and methylene groups undergo ring-expansion reactions to afford 1,4-dithiepins and 1,4-dithiins in dry CH(2)Cl(2) at room temperature in good yields.     

Preparation and mass spectra of 2,5-diaryl-1,4-dithiins

2 Seven5-diaryl-1,4-dithiins were prepared from phenacyl halides via the corresponding Bunte salts. The mass spectra showed a number of similarities within this series of compounds. Various dipositive ions were observed in all cases while the unsubstituted and p-methyl derivatives formed tripositive ions. Ir, nmr, and chemical analysis were also completed and reported.     

Selective synthesis, structure and oxidation properties of isomeric 1,4-dithiins fused to two benzo[b]thiophenes

Two novel isomers of 1,4-dithiins fused to two benzo[b]thiophenes on both sides were obtained by selective synthetic methods via the corresponding sulfides. The crystal structures of two dithiins were determined by X-ray crystallographic analyses. Examination of oxidation properties of the dithiins showed interesting results by CV measurement. The ESR spectra of chemically oxidized dithiins indicated formation of stable radical cations.     

Synthesis, electrochemistry, and gas-phase photoelectron spectroscopic and theoretical studies of 3,6-bis(perfluoroalkyl)-1,2-dithiins

3,6-bis(trifluoromethyl)- and 3,6-bis(pentafluoroethyl)-1,2-dithiin (1a,b), the first known perfluoroalkyl-substituted 1,2-dithiins, were synthesized from (Z,Z)-1,4-bis(tert-butylthio)-1,3-butadiene (2) to evaluate the effects of electron-withdrawing groups on the ionization and oxidation potentials of 1,2-dithiins. Analysis of the photoelectron spectra of 1a and 1b provided a basis for assigning orbital compositions. Ab initio calculations on these compounds showed that they adopt a twist geometry as does 1,2-dithiin (1c) itself. Cyclic voltammetric studies on 1a and 1b revealed a reversible oxidation followed by an irreversible oxidation at much more positive potentials than for 1,2-dithiin and 3,6-dimethyl-1,2-dithiin (1d). The oxidation potentials determined electrochemically do not correlate with the ionization potentials determined by photoelectron spectroscopy. This result supports the previously advanced hypothesis that there is a geometry change on electrochemical oxidation leading to a planar radical cation.     

New insight into the reaction of singlet oxygen with sulfur-containing cyclic alkenes: dye-sensitized photooxygenation of 5,6-dihydro-1,4-dithiins

The reaction of 3-methyl-5,6-dihydro-1,4-dithiins with singlet oxygen affords dicarbonyl compounds and/or ring-contracted ketosulfoxides, the latter regio- and stereoselectively, depending on the nature of the substituent at C-2 and on the reaction conditions. In competition with normal fragmentation, the intermediate dioxetanes, derived from [2 + 2] cycloaddition of singlet oxygen to the double bond, undergo an intramolecular oxygen transfer to the sulfur-1 atom, leading to labile epoxide intermediates. The latter convert to cis- and trans-ketosulfoxides through a non-concerted S-4 migration. This pathway is promoted by the electron-withdrawing group at C-2 and, for monosubstituted amide, by the solvent basicity. S-Oxidation of dithiins is insignificant, except for the monosubstituted amide derivative or in the presence of protic species, and occurs selectively at the S-1 atom.     

Carbon-13 NMR investigation of 2,5-diaryl-1,4-dithiins

The ¹³C NMR spectra of eight 2,5-diaryl-1,4-dithiins were recorded and signals were assigned. A linear correlation was observed between the electronegativity of the substituent groups on C-10,10′ and the chemical shifts of C-10,10′ after applying corrections for the magnetic anisotropic effect of the substituents. A Hammett correlation was found between the ¹³C chemical shifts of C-3,6 and C-7,7′ and the σ_p⁺ parameter associated with the substituents on C-10,10′. Extended electronic interaction between the π system of the aryl group and the π system of the dithiin ring was suggested by the observance of an alternating behavior in the magnitude of the substituent effects on the ¹³C shifts of C-2,5 and C-3,6. An alternating effect was also noted in the magnitude of the long-range ¹³C? F coupling constants for these same carbon signals in 2,5-(10,10′-difluoro)diphenyl-1,4-dithiin.     

Evidence of Transannular Bonding Interaction between Two Sulfur Atoms on Photolysis of Naphtho[1,8-ef][1,4]dithiepins

Naphtho[1,8-ef][1,4]dithiepins 5 were prepared by the reaction of naphtho[1,8-de]-1,3-dithiins 3 with diethyl diazomalonate in the presence of copper acetylacetonate. The X-ray crystallographic analysis of 2,3-dihydro-2,2-bis(ethoxycarbonyl)-3-phenylnaphtho[1,8-ef][1,4]dithiepin (5a) revealed that the S.S distance is shorter than the sum of their van der Waals radii, indicating that compounds 5 have a strong through-space interaction between the two sulfur atoms. Direct irradiation of 5 with a 500 W high-pressure mercury lamp (313 nm) at room temperature gave the corresponding olefins 6 and naphtho[1,8-cd]-1,2-dithiole (1) quantitatively. The quantum yields of the consumption of 5a and the formation of 6aand 1 were 0.34. The mechanism of this reaction was investigated by examining the effect of sensitization and light intensity. The results indicate that the reaction may proceed by a one-photon process from an excited singlet state. Ab initio calculations were carried out on model compound 7, and it was shown that the excitation to the S(1) state causes a bonding interaction between the two sulfur atoms, making the reaction possible.     

Extrusion reactions-VII

ω-(2,6-Dimethyl-4-pyrimidinylthio-(4), 2-methyl-4-quinazolinylthio-(9), and 4-oxo-2-quinazo-linylthio)-(10) acetophenones with hydrochloric or perchloric acid provide 2,5-diaryl-1,4-dithiins (7) whereas α)-(6-methyl-4-pyrimidinylthio) acetophenones (11) with aq HCl/HClO₄, or POCl₃ followed by hydrolysis provide 1-(4-aryl-2-thiazolyl)-2-propanones (12). Likewise, 2-(6-methyl-4-pyrimidinylthio) cyclohexanone (13) give the thiazole derivative (14).     

Unusual chemical behaviour of silylated 1,2-dithiins under Lewis acid conditions

Different silylated 1,2-dithiins, obtained through self-dimerization of the related α,β-ethylenic thioacylsilanes, in the presence of AlCl₃ show an unusual rearrangement leading in good yields to novel silyl-endodisulfide bicyclic systems.     

An easy access to α,β-unsaturated thioacylsilanes: a useful route to silylated 1,2-dithiins

Treatment of different silylated allenes with hexamethyldisilathiane (HMDST) in the presence of CoCl₂·6H₂O affords an easy and high yielding access to α,β-unsaturated thioacylsilanes, which undergo a self-dimerization reaction to afford polyfunctionalized 1,2-dithiins as the major products.     

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.     

Chemoselective annulation of 1,3-dithiin, -thiazine and -oxathiin rings on thiazoles using a green protocol

Tandem Knoevenagel and Michael reactions of 3-arylrhodanines, aromatic aldehydes and ammonium N-aryldithiocarbamates diastereoselectively yield dithioesters, thiazol-5-ylmethyl N-aryldithiocarbamates, under solvent-free microwave irradiation conditions in a one-pot procedure. Under the same conditions, the dithioesters are chemoselectively and expeditiously annulated with montmorillonite K-10 clay, Li⁺-montmorillonite clay and I₂ to give thiazolo-1,3-dithiins, -thiazines and -oxathiins, respectively.     

Thermotropic copolyesters containing the 1,4-cyclohexylenedimethylene spacer

Poly[oxy(2-methyl-1,4-phenylene)oxyterephthaloyl-co-oxy(2-methyl-1,4-phenylene)oxy-1,4-cyclohexanediacetoyl] (I), poly[oxy(2-chloro-1,4-phenylene)oxyterephthaloyl-co-oxymethylene-1,4-cyclohexylenemethyleneoxyterephthaloyl] ( II ), and poly[oxy(2-methyl-1,4-phenylene)oxyterephthaloyl-co-oxymethylene-1,4-cyclohexylenemethyleneoxyterephthaloyl] ( III ) were synthesized and shown to form birefringent fluid states in the melt.     

Reaction of thiosalicylic acid with 1,4-quinones and cyclization of the resulting arylsulfanylbenzoic acids

Thiosalicylic acid reacts with 1,4-benzoquinone to give 2-(1,4-dihydroxyphenylsulfanyl)benzoic acid which undergoes intramolecular cyclization to 1,4-dihydroxythioxanthen-9-one in the presence of dehydrating agents. Cyclization of arylsulfanylbenzoic acids obtained by reaction of thiosalicylic acid with 1,4-naphtho- and anthraquinones leads to 1,4-quinone derivatives, benzo- and naphthothioxanthenetriones.