2.3- dihydrothiophene

The names A -thiole and 3-thiole have previously been used for 2,5-dihydrothiophene. A general synthesis for 2,5-dihydrothiophenes with different substituents is based on the Michael addition of a-sulfanylcarbonyl compounds to vinyl phosphonium salts, followed by an intramolecular Wittig reaction  

5-Dihydrothiophenes are oxidized to 1,1-dioxides by m-chloroperoxybenzoic acid. These compounds are also accessible by (4 + 1)-cycloaddition of 1,3-dienes and sulfur dioxide. For instance, butadiene reacts even at room temperature with liquid sulfur dioxide to give an adduct 2,5-dihydrothiophene-l,1-dioxide, commonly known by the trivial name 3-suhnlene  

Following Woodward, such conversions are called chdetropic reactions. The LUMO of the 1,3-diene surrounds the nonbonding electron pair of sulfur like the claws of a crab (Greek chele). 

3-Sulfolenes are masked 1,3-dienes [96]. At about 150 °C they undergo (4+ 1)-cycloreversion into 1,3-dienes and sulfur dioxide. As this is a thermal concerted reaction, this cycloreversion proceeds in a disrotatory manner according to the Woodward-Hoffmann rules. Thus, a ds-2,5-disubstituted 3-sulfolene stereospecifically yields an (F,E)-l,3-diene, while the trans-diastereomer gives an (F,Z)-1,3-diene  

For multistep syntheses that include a Diels-Alder reaction, corresponding 1,3-dienes are necessary. They can be prepared by the method described. In many cases, the 1,3-diene is not isolated, but the Diels-Alder reaction is carried out with 3-sulfolene and dienophile in boiling xylene. 

Mixtures of endo- and exo-diastereomers are usually formed. The reactivity of l,3-diphenylbenzo[c]-thiophene in [4+2] cycloadditions is distinctly lower. Acetylene dienophiles yield adducts which, on heating, are converted into the corresponding substituted naphthalenes with loss of sulfur  

3-Sulfolenes are masked 1,3-dienes [33]. At about 150°C they undergo [4+1] cycloreversion (cycloelimination) into 1,3-dienes and sulfur dioxide. As this is a thermal concerted reaction, it proceeds in a 

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Production. Sulfolane is produced domestically by the Phillips Chemical Company (Borger, Texas). Industrially, sulfolane is synthesized by hydrogenating 3-sulfolene [77-79-2] (2,5-dihydrothiophene-l,1-dioxide) (2), the reaction product of butadiene and sulfur dioxide ... 

Reduction and Hydrodesulfurization. Reduction of thiophene to 2,3- and 2,5-dihydrothiophene and ultimately tetrahydrothiophene can be achieved by treatment with sodium metal—alcohol or ammonia. Hydrogen with Pd, Co, Mo, and Rh catalysts also reduces thiophene to tetrahydrothiophene [110-01-0] a malodorous material used as a gas odorant. 

The effect on strain energy of introducing unsaturation into these rings has been evaluated in the cases of 2,3- and 2,5-dihydrothiophene, where the additional values are 18 and 15.8 kJ mol ... 

The methiodide of 2,5-dihydrothiophene (239) is transformed in high yield to Z)-l-(methylthio)buta-l,3-diene (240) on treatment with alkali (81AJC1017). The thermal cheletropic extrusion of sulfur dioxide from both cis and trans isomers of 2,5-dihy-drothiophene 1,1-dioxides is highly stereospecific. For example, c/5-2,5-dimethyl-2,5-dihydrothiophene 1,1-dioxide (241) yields ( , )-hexa-2,4-diene (242) and sulfur dioxide (75JA3666, 75JA3673). 

Perfluoronaphthalene undergoes an intermolecular substitution followed by intramolecular cyclLzation on reaction with allyl bromide and mercaptide ion to furnish a dihydrothiophene denvative in high yield [34] (equation 23). 

Dichlorotetrafluoro-2,5-dihydrothiophene is converted to the perfluoro-p-dithiin, probably by an addition-elimination process [i] (equation 3). 

Does the fact that thiophene reacts similarly to benzene mean that it is aromatic One way to tell is to calculate first and second hydrogenation energies of thiophene, leading to dihydrothiophene and tetrahydrothiophene, respectively. (The energy of hydrogen is provided at right.)... 

Dichlorothiophene has become easily available through chlorination and dehydrochlorination of tetrahydrothiophened Another example of the aromatization of tetrahydrothiophene derivatives is the preparation of 3-substituted thiophenes by the reaction of 3-ketotetrahydrothiophene with Grignard reagents followed by the aromatization of the intermediate dihydrothiophene. Recent gas chromatographic analysis showed, however, that 2,3-dichlorothio-phene is the main product from the dehydrochlorination of tetra-chlorotetrahydrothiophene. 

Therefore, it may also be possible to aromatize the dihydrothiophene derivatives (93) obtained through the acid catalyzed rearrangement of a-hydroxymethylene-y-thiobutyrolactone derivatives (92) in ethanold °... 

Catalytic reduction of thiophenes over cobalt catalysts leads to thiolane derivatives, or hydrocarbons. " Noncatalytic reductions of thiophenes by sodium or lithium in liquid ammonia leads, via the isomeric dihydrothiophenes, to complete destructions of the ring system, ultimately giving butenethiols and olefins. " Exhaustive chlorination of thiophene in the presence of iodine yields 2,2,3,4,5,5,-hexachloro-3-thiolene, Pyrolysis of thiophene at 850°C gives a... 

Sulfolene (2,5-dihydrothiophene-l,1-dioxide) EK, MCB Isopropenyl acetate MCB Dimedon EK, MCB... 

N. A-Diethyl-2.3-dihydro-8//-thieno[2,3-r/]azcpin-7-amine (20), which is obtained in 49 % yield by photolysis of 6-azido-2,3-dihydrothiophene in a mixture of diethylamine and tetrahydro-furan. on treatment with bromine yields the fully unsaturated derivative 21.1,4... 

C3H402S, 2H-Thiete 1,1-dioxide C4H602S, 2,5-Dihydrothiophene 1,1-dioxide C4H602S, 2,3-Dihydrothiophene 1,1-dioxide CsHgOjS, 2,5-Dihydro-2-methylthiophene 1,1-dioxide C5H802S, 2,5-Dihydro-3-methylthiophene 1,1-dioxide... 

Methyl-2,5-dihydrothiophene was converted into the corresponding S-oxide 4 in 57% yield after treatment with 30% excess of hydrogen peroxide for 60 h. By the same procedure the sulphoxides 5 derived from thiophene and its a-substituted analogues were also prepared18. 

Under certain basic conditions 2,5-dihydrothiophene 1,1-dioxides undergo ring opening reactions108,109 and the resulting buta-l,3-dienyl sulfinate ions may be alkylated... 

A procedure for a synthesis of dienyl sulfoxides (232 and 233) involves ring opening of dihydrothiophene 1,1-dioxide (231) by two molar equivalents of Grignard reagent (equation 141)136. The yields are usually in the 20-66% range. Similarly, treatment of the bicyclic sulfones 234, with 2 equivalents of phenylmagnesium bromide, produced a mixture of 1,4-dienylic sulfoxides (equation 142)136. 

Dihydrodithiin sulphoxides, synthesis of 243 Dihydrothiophene dioxides, reactions of 653 /(,/( -Dihydroxyketones 619 Dimerization, photochemical 877, 884 Dimethyl sulphoxide anion of - see Dimsyl anion hydrogen bonding with alcohols and phenols 546-552 oxidation of 981, 988 photolysis of 873, 874, 988 radiolysis of 890-909, 1054, 1055 self-association of 544-546 Dimsyl anion... 

Dimethylene-2,3-dihydrothiophene (37, Figure 2.3) is the thiophene analog [38] of o-quinodimethanes and has been used to develop a Diels-Alder-based synthetic approach to benzothiophene derivatives. Generated in situ by treating the trimethylsylyl ammonium derivatives 38 or 39 with Bu4N F , it... 

The reaction of furan with 2,5-dihydrothiophene-3,4-dicarboxylic anhydride is remarkable (Scheme 6.19). Furan is a poor diene and requires high pressure to affect cycloadditions [39]. On the other hand, high temperatures are forbidden because cycloaddition products derived from furan undergo cycloreversion under these conditions. In 5.0m LP-DE, the Diels-Alder reaction of furan with 2,5-dihydrothiophene-3,4-dicarboxylic anhydride proceeds at room temperature and atmospheric pressure in 9.5 h with 70 % yield and with the same diastereos-electivity found when the reaction is carried out under high pressure [40]. 

This category is represented in the facile reaction of o-phenylenediamine (408) with 4-benzoyl-5-phenyl-2,3-dihydro-2,3-thiophenedione (409) (in toluene at 20°C for 30 min) to afford 3-(a-benzoyl-p-mercaptostyryl)-2(l//)-qumoxalinone (410) in 98% yield " also in the complicated reaction of 3-methyl-2,2,4-trinitro-2,5-dihydrothiophene 1,1-dioxide (411) with 2 equiv of ethyl 4-aminobenzoate (412) (in acetonitrile but no further details) to give ethyl 2-(p-ethoxycarbonylphenyl)-3-(l-methyl-2-nitrovinyl)-6-quinoxalinecarboxylate (413) in 51% yield.Several... 

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