2.5- dihydrothiophene-1,1 -dioxides

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). 

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... 

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... 

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... 

Dihydrothiophene-1,1-dioxides (42) and 2,17-dihydrothiepin-1,1-dioxides (43) undergo analogous 1,4 and 1,6 eliminations, respectively (see also 17-38). These are concerted reactions and, as predicted by the orbital-symmetry rules (p. 1067), the former is a suprafacial process and the latter an antarafacial process. The rules also predict that elimination of SO2 from episulfones cannot take place by a concerted mechanism (except antarafacially, which is unlikely for such a small ring), and the evidence shows that this reaction occurs by a non-concerted pathway.The eliminations of SO2 from 42 and 43 are examples of cheletropic reactions, which are defined as reactions in which two a bonds that terminate at a single atom (in this case the sulfur atom) are made or broken in concert. 

The most synthetically useful cheletropic elimination involves 2,5-dihydrothiophene-1,1-dioxides (sulfolene dioxides). At moderate temperatures they fragment to give dienes and sulfur dioxide.301 The reaction is stereospecific. For example, the dimethyl derivatives 22 and 23 give the E,E- and Z,E-isomers of 2,4-hexadiene, respectively, at temperatures of 100°-150°C.302 This stereospecificity corresponds to disrotatory elimination. 

The thiophene ring system can be utilized as a synthetic scaffold for the preparation of nonthiophene materials as the sulfur moiety can be removed by reduction (desulfurization) or extrusion (loss of SO2). The extrusion of sulfur dioxide from 3-sulfolenes (2,5-dihydrothiophene 1,1-dioxides) give dienes (butadienes or o-quinodimethanes) that can be utilized to prepare six-membered rings by cycloaddition chemistry. For example, thermolysis of 3-sulfolene 120 provided tricyclic pyrazole 122 via an intramolecular cycloaddition of the o-quinodimethane 121 that results by extrusion of sulfur dioxide <00JOC5760>. Syntheses of 3-sulfolenes 123 and 124 <00S507> have recently been reported. 

Dihydrothiophene 1,1-dioxide (butadiene sulfone, or 3-sulfolene) was purchased from the Aldrich Chemical Company, Inc. 

A flask was charged with 2,5-dihydrothiophene-1,1-dioxide (0.85 mol) and heated to 66°C for 30 minutes and then treated with potassium f-buthoxide (0.25 mol) and reacted for 6 hours. The solution was then cooled and neutralized by adding 35% hydrochloric acid and concentrated. The residue was treated with 1 liter of toluene, filtered, and reconcentrated. The residue was distilled at 130-135°C 2mmHg and 22.0 g of product isolated. 

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-1,1-dioxide) (2), the reaction product of butadiene and sulfur dioxide ... 

Intramolecular [4 + 2] cycloaddition reactions of enamides have provided a route to hydroindole and hydroquinoline ring systems (80JA3294,5274). In this work, the diene portion was initially masked as a 2-substituted 2,5-dihydrothiophene 1,1-dioxide. Thus, reaction of the acid chloride (312) with 3,4,5,6-tetrahydropyridine (311) afforded the masked enamido diene (313), which was converted to the enamido diene (314) upon brief refluxing in xylene. Thermolysis of (314) afforded the hydrolulolidine (315) in 45-55% yield. Additionally, (313) could be transformed to (315) directly by passage of a 1% solution in toluene through a vertical tube (600 °C oven temperature) (Scheme 67). The method was used to prepare a known precursor to aspidospermine. 

Trivial names which have found use in this article are thiolane (for tetrahydrothiophene), sulfolane (for tetrahydrothiophene 1,1-dioxide) and sulfolene (for 2,5-dihydrothiophene 1,1-dioxide). As with usual practice, thienyl refers to the radical corresponding to phenyl in benzene chemistry, and thenyl is analogous to benzyl . 

Sulfur-hydrogen scalar coupling has been observed for a solution of 2moldm 2,5-dihydrothiophene 1,1-dioxide (butadiene sulfone) 90, in acetone. A partially resolved triplet, of total width 18 Hz, collapses to a singlet, width 7 Hz, when proton decoupling is applied. The major coupling is attributed to a vicinal interaction between the sulfur and olefinic protons, by comparison of the carbon spectrum of diethyl ketone (the carbonyl carbon resonance exhibits a septet) and the sulfur spectrum of sulfolane (the sulfur peak shows no structure). This was confirmed by selectively decoupling at the two relevant proton frequencies in turn. 

In an unusual reaction, 3-(piperidinomethyl)-2,5-dihydrothiophene 1,1-dioxide was obtained when 2,5-bis(trimethyl-silybthiophene 1,1-dioxide was reacted with excess piperidine in an aprotic solvent (Equation 59) <2000EJ03139>. 

Dihydrothiophene 1,1-dioxide in the presence of l,8-diazabicyclo[5.4.0]undec-7-ene (DBU) reacts with CO2 to give the carboxylic acid (Equation 69), which is a stable precursor to l,3-butadiene-2-carboxylic acid <2003SC3643>. The reaction proceeds through initial deprotonation at the 2a-position the resonance-stabilized carbanion thus generated reacts with CO2 to form the carboxylate. Abstraction of a proton from the 3-position by another molecule of the base generates a dianion, which isomerizes to the stable dianion as shown in Scheme 39. Final protonation produces 3-sulfolene-3-carboxylic acid. 

Reaction of 1,6-diynes 414 and 415 with Pdl2, CO, and O2 in methanol followed by treatment with Et3N affords hi- and terthiophenes 416 and 417, respectively <1999T485>. 2,5-Dihydrothiophene 1,1-dioxide 419 is synthesized by Ru-catalyzed hydrative cyclization of diyne 418 (Equation 12) <20050L2097>. 

There are other kinds of cycloadditions, too. The [4 + 1] cycloaddition, a cheletropic reaction, usually goes in the retro direction for entropic reasons. 3-Sulfolene (butadiene sulfone, 2,5-dihydrothiophene 1,1-dioxide) undergoes a [4 + 1] retro-cycloaddition to generate S02 and 1,3-butadiene, which can undergo a Diels-Alder reaction with a dienophile. It is much more convenient to... 

Five-membered, cyclic allylic sulfones, except the parent 2,5-dihydrothiophene 1,1 -dioxide, underwent smooth addition of dichlorocarbene generated from chloroform/base/phase-transfer catalyst giving 4. ... 

---