[77-79-2] · C4H6O2S · 3-Sulfolene · (MW 118.17)
Alternate Names: butadiene sulfone; 2,5-dihydrothiophene 1,1-dioxide.
Physical Data: mp 65 °C; dec above ca. 110 °C.
Solubility: sol water, organic solvents.
Form Supplied in: white solid, widely available.
Handling, Storage, and Precautions: nonflammable and nonhygroscopic, odorless, and indefinitely stable; skin irritant and under investigation as a potential carcinogen2 (RTECS #XM9100000).
3-Sulfolene (1) is a convenient solid source for in situ generation of 1,3-Butadiene, for example in Diels-Alder reactions (eq 1).3 It affords Sulfur Dioxide and butadiene by a concerted disrotatory4-6 thermal process. The liberated SO2 may cause acid-catalyzed reactions (eq 2).7
Under mildly basic conditions, equilibrium is established between the 2-isomer (42%) and 3-isomer (58%).8,9 For substituted rings, the equilibrium concentrations are strongly substituent dependent. Sulfolene serves as a platform for preparing conjugated dienes (eq 3)10 by substitution followed by SO2 elimination. Very sensitive conjugated dienes such as those of the
dendralene type (eq 7)11 can be prepared in this manner.
Typical electrophilic additions occur readily. The dibromo derivative is a convenient source of the very reactive thiophene dioxide (eq 4).12
PhSX and PhSeX give trans additions and oxidative removal of PhSeOH affords the substituted 3-sulfolene (eq 5).13 Dienes such as 2,3-bis(phenylthio)butadiene have been prepared by manipulation of the addition products.14 Products of peracid oxidation or carbene or nitrene addition afford divinyl ethers, 1,4-dienes,15 divinylamines,16 or cyclobutenes17 by thermal extrusion of SO2 (eq 6).
The epoxides are often elaborated further to regenerate a substituted 3-sulfolene (eq 7).
Apparently anomalous nucleophilic additions actually proceed by prior isomerization to the vinyl sulfone (2-sulfolene) (eq 8). Other processes are also affected by this tautomerism.8
Substituted (1) can be obtained by addition of SO2 to dienes or nucleophiles to thiophene dioxides,1 by alkylations of anions derived from (1), or by peracid oxidation of substituted 2,5-dihydrothiophenes which occurs regioselectively at sulfur (eq 9).18,19 The alkyl-substituted dihydrothiophenes are best prepared from vinylphosphonium salts,18,19 while functionalized systems can be prepared using vinyl phosphonates.20
Deprotonation to form a delocalized carbanion occurs under basic conditions. Reactions with electrophiles usually occur a to the sulfone (eq 3) to afford the 2-substituted 3-sulfolene,21 but electronic and steric effects of existing substituents strongly affect the alkylation regioselectivity.22 Equilibration with D2O affords the 2,2,5,5-tetradeutero derivative,23 which is a convenient source of specifically deuterated butadiene-d4. This has been used in syntheses of deuterated anthracenes24 and cyclohexenes,25 etc. Dialkylation preferentially proceeds to give the 2,5-disubstituted isomer.26,27 The presence of a 2-trimethylsilyl or -stannyl substituent can be used advantageously to access the 2-monosubstituted or the 2,2-disubstituted system which may be spiro in nature (eq 10).26,28
The alkylation stereochemistry controls the geometry of the diene and ultimately the stereochemistry of the Diels-Alder product. The trans 2,5-disubstituted isomer is formed fastest but the cis isomer is more stable and its thermal decomposition to the (E,E)-diene is faster than that of the isomeric trans isomer to the (E,Z)-diene. Therefore by heating the trans isomer in the presence or absence of small amounts of base, either the (E,E)- or the (E,Z)-dienes can be obtained selectively (eq 11).27
Other methodologies have been used to obtain the cis isomer (e.g. eq 12)29
Aldol reactions and acylations30 occur at the 2-position. Aldol condensations with various heterocyclic aldehydes occur in low yields (ca. 10%), but the products have been used as precursors to conducting polymers (eq 13).31
John M. McIntosh
University of Windsor, Ontario, Canada