Methods for the preparation of thiophene S-oxides, their roles in thiophene metabolism, and the structures and chemical reactivity of these compounds, are discussed.
From heats of formation obtained from combustion experiments, Wheland determined the resonance energies of different heteroaromatic compounds to be: 29 kcal/mol for thiophene > 21 kcal/mol for pyrrole > 16 kcal/mol for furan: G. W. Wheland, Resonance in Organic Chemistry, Wiley, NY, 1955, p. 99. From structural features, i.e. from deviations of peripheral bond orders (and the sum of bond order differences) the aromaticity of simple heteroaromatic compounds was determined to be of the order: thiophene > selenophene > tellurophene > furan:
Meth-CohnO., and von VuurenG., J. Chem. Soc., Chem. Commun., 1984, 190.
6.
Meth-CohnO., and von VuurenG., J. Chem. Soc., Perkin Trans. 1, 1986, 233.
7.
GillespieR.J., Murray-RustJ., Murray-RustP., and PorterA.E.A., J. Chem. Soc., Chem. Commun., 1978, 83.
8.
HeldewegR. F., and HogeveenH., Tetrahedron Lett., 1974, 75.
9.
Prochazka et al. claimed to have detected the parent thiophene S-oxide in solution under these conditions: ProchazkaM., and PalecekM., Collect. Czech Chem. Commun., 1967, 32, 3049.
BoydD.R., SharmaN.D., HaugheyS.A., MaloneJ.F., McMurrayB.T., SheldrakeG.N., AllenC.C.R., and DaltonH., J. Chem. Soc., Chem. Commun., 1996, 2363.
32.
For a recent review on benzothiophene S-oxides, see: ThiemannT., ArimaK., KumazoeK., and MatakaS., Rep. Inst. Adv. Study Kyushu Univ., 2000, 14, 141; Chem. Abstr., 2001, 134, 326 318a.
33.
NakayamaJ., SanoY., SugiharaY., and IshiiA., Tetrahedron Lett., 1999, 40, 3785.
34.
FurukawaN., ZhangS.-Z., HornE., TakahashiO., and SatoS, Heterocycles, 1998, 47, 793.
35.
The non-planar structure of thiophene S-oxides has also been predicted by calculations: (a) HashmallJ.A., HorakV., KhooL.E., QuicksallC.O., and SunM.K., J. Am. Chem. Soc., 1981, 103, 289
36.
AmatoJ.S., KaradyS., ReamerR.A., SchlegelH.B., SpringerJ.P., and WeinstockL.M., J. Am. Chem. Soc., 1982, 104, 1375 (both ab initio) and
37.
RojasI., J. Phys. Org. Chem.1992, 5, 74 (MNDO).
38.
MockW.L.10 has calculated the free energy of activation for the inversion, ΔG‡, to be around 14.8 kcal/mol by determining the coalescence temperature of the diastereotopic methylene protons of 2,5-di-t-octylthiophene S-oxide.
39.
PouzetP., ErdelmeierI., GinderowD., MornonJ.-P., DansetteP.M., and MansuyD., J. Heterocycl. Chem., 1997, 34, 1567.
40.
ThiemannT., OhiraD., ArimaK., SawadaT., MatakaS., MarkenF., ComptonR.G., BullS.D., and DaviesS.G., J. Phys. Org. Chem., 2000, 13, 648.
41.
BonginiA., BarbarellaG., ZambianchiM., ArbizzaniC., and MastragostinoM., J. Chem. Soc., Chem. Commun., 2000, 439.
42.
For a more complete list of possible dienophiles in the reactions with thiophene S-oxides, see ref. 8h.
43.
ThiemannT., OhiraD., LiY.Q., SawadaT., MatakaS., RauchK., NoltemeyerM., and de MeijereA., J. Chem. Soc., Perkin Trans.1, 2000, 2968.
44.
(a) ZengH.-P., and EguchiS., Synlett, 1997, 175
45.
ThiemannT., FujiiH., DongolK.G., MatakaS., WaltonD., BarrowM., and DerrickP.J., New J. Chem., to be submitted.
46.
OhiraD., ThiemannT., and KitamuraT., unpublished results.
47.
(a) TorssellK., Acta Chem. Scand. (Ser. B) 1976, 353
48.
NaperstkowA.M., MacaulayJ.B., NewlandsM.J., and FallisA.G., Tetrahedron Lett., 1989, 30, 5077
49.
LiY.-Q., ThiemannT., SawadaT., and TashiroM., J. Chem. Soc., Perkin Trans.1, 1994, 2323
50.
ThiemannT., LiY.-Q., MatakaS., and TashiroM., J. Chem. Res., 1995 (S) 384; (M) 2364
LiY.Q., ThiemannT., MimuraK., SawadaT., MatakaS., and TashiroM., Eur. J. Org. Chem., 1998, 1841.
55.
(a) CieplakA.S., J. Am. Chem. Soc., 1981, 103, 4540
56.
CieplakA.S., TaitB.D., and JohnsonC.R., J. Am. Chem. Soc., 1989, 111, 8447
57.
for a review, see: CieplakA. S., Chem. Rev., 1999, 99, 1265.
58.
WerstiukN.F., and MaJ., Can. J. Chem., 1994, 72, 2493.
59.
For semiempirical studies at the AM1 level, see: JursicB.S., J. Heterocycl. Chem., 1995, 32, 1445.
60.
OtaniT., SugiharaY., IshiiA., and NakayamaJ., Chem. Lett., 2000, 744.
61.
OtaniT., SugiharaY., IshiiA., and NakayamaJ., Tetrahedron Lett., 2000, 41, 8461.
62.
ThiemannT. in collaboration with the National Cancer Institute, Bethesda, Maryland, U.S.A., as part of its Developmental Therapeutics Program.
63.
NakayamaJ.. have isolated 1,3-dimethyl-2-imidazolidinone upon reaction of 3,4-di-t-butylthiophene S-oxide with 2-methylene-1,3-dimethylimidazolidine (toluene, reflux). Seemingly this reaction is more complex, and does not involve a direct oxygen transfer from the thiophene S-oxide to the methyleneimidazolidine. Thus, a 1a,4a-dihydro-1H-cyclopropa[b]thiophene, and not the corresponding thiophene is isolated as the second product: NakayamaJ., TakayamaJ., SugiharaY., and IshiiA., Chem. Lett., 2001, 758.
ThiemannT., ArimaK., OhiraD., KumazoeK., and MatakaS., Preparation, and Photochemistry of Thiophene S-oxides, ECSOC-4 Proceedings (WirthT., KappeC.O., FelderE., DiedrichsenU., and LinS.-K., eds.), ISBN 3-906980-05-7; Chem. Abstr., 2001, 135, 288 649v
67.
ArimaK., OhiraD., MatakaS., and ThiemannT., submitted to Photochem. Photobiol. Sci.
68.
OhiraD., MSc thesis, Kyushu University, 2000.
69.
Transformations from thiophene, and selenophene derivatives to furans have been reported before, albeit under different conditions. Thus: diphenylthiophene S-oxide forms diphenyl-furyl-(diphenylthienyl)sulfoxide when subjected to hydrogen peroxide/trifluoro acetic acid. In the mass spectrum (EI-mode, 70 eV), unsubstituted thiophene S,S-dioxide shows as its most intense peak the furan radical cation. The pyrolysis of thiophene S,S-dioxides has long been known to give furans: (a) van TilborgW.J.M., and PlompR., Recl. Trav. Chim. Pays-Bas, 1977, 96, 282
70.
NakayamaJ., SugiharaY., TeradaK., and ClennanE.L., Tetrahedron Lett., 1977, 31, 4473.
71.
SkaugsetA.E., RauchfussT.B., and SternC.L., J. Am. Chem. Soc., 1990, 112, 2432.
72.
(a) TanakaK., WangS., and YamabeT., Synth. Metals, 1989, 30, 57; other calculations followed: (a) BakhshiA.K., Solid State Commun., 1995, 94, 943.
