Se-Phenyl p-Tolueneselenosulfonate1

[68819-94-3]  · C13H12O2SSe  · Se-Phenyl p-Tolueneselenosulfonate  · (MW 311.28)

(undergoes 1,2-additions to alkenes, allenes, dienes, and alkynes, affording various unsaturated sulfones after selenoxide elimination or sigmatropic rearrangement1)

Physical Data: mp 79.5-80 °C.

Solubility: sol chloroform, dichloromethane, THF, benzene.

Form Supplied in: yellow, crystalline, odorless solid.

Preparative Methods: add p-Toluenesulfonylhydrazide in methanol dropwise to an equimolar amount of Benzeneseleninic Acid in methanol at 0 °C; cool at -5 °C overnight, filter the highly pure crystalline selenosulfonate (96% yield);2 alternatively, use 2 equiv p-Toluenesulfinic Acid instead of p-toluenesulfonylhydrazide;3 Se-phenyl benzeneselenosulfonate is prepared in the same way and can be employed similarly for most purposes.

Purification: recrystallization from methanol.

Handling, Storage, and Precautions: routine handling is possible; for prolonged storage, keep in the dark at 0 °C; probably toxic. Use in a fume hood.

Selenosulfonation of Alkenes, Allenes, and Dienes.

The selenosulfonate adds stereospecifically (anti) and regioselectively (Markovnikov) to alkenes in the presence of Boron Trifluoride Etherate to afford 1,2-adducts (eq 1).4 The addition can also be effected by a nonstereospecific radical process, initiated thermally in the presence of Azobisisobutyronitrile (AIBN), or photochemically, to give anti-Markovnikov products (eq 2).3,4 These processes are known as selenosulfonations.4 Selenoxide syn elimination of the adducts can be effected with m-Chloroperbenzoic Acid (m-CPBA) or Hydrogen Peroxide, and affords high yields of the corresponding vinyl sulfones.

Allenes undergo radical selenosulfonation with regioselective incorporation of the sulfonyl moiety at the central carbon atom, producing 2-sulfonyl allylic alcohols after oxidation and [2,3]-sigmatropic rearrangement (eq 3).5 Conjugated dienes react with the selenosulfonate in the presence of Lewis acids to afford chiefly the corresponding 1,2-adducts, in turn producing 2-sulfonyl-1,3-dienes after selenoxide elimination (eq 4),4,6 while 1,6-dienes are converted into cyclopentanes by radical cyclization.7

Selenosulfonation of Alkynes.

The radical selenosulfonations of alkynes proceed in a stereo- and regioselective manner to give the products of anti addition and anti-Markovnikov orientation in generally high yield.8 Subsequent selenoxide eliminations produce alkynic sulfones from terminal alkynes (eq 5) and allenic sulfones from internal ones (eq 6). Moreover, the initial adducts can be alkylated in the a-position and isomerized to the corresponding allylic sulfones under base-catalyzed conditions, thereby also providing access to allenic sulfones from terminal alkynes (eq 7).9 The adducts or their selenoxides also react with various nucleophiles by addition-elimination or elimination-addition processes to give the products of overall substitution of the selenium residue (eq 8). Possible nucleophiles include organocuprates, alcohols, amines, cyanide, active methylene compounds, dithianes, and propargylic anions.8a,10 When such reactions are employed in conjunction with reductive desulfonylation, the overall transformation renders alkynes the synthetic equivalents of vinyl cations.

Enynes with terminal alkyne moieties cleanly afford the products of 1,2-addition to the triple bond (eq 9), but more highly substituted derivatives and those containing terminal alkene groups give more complex mixtures containing the products of addition to the double bond, as well as 1,4-adducts.11 Products such as the example in eq 9 smoothly generate allenic alcohols after oxidation and [2,3]-sigmatropic rearrangement. 1,4-Dichloro-2-butyne can be employed as an enyne equivalent, since reductive dehalogenation generates an additional unit of unsaturation. The resulting 2,3-adduct can be used to prepare 3-substituted 2-sulfonyl-1,3-dienes,11 as shown in eq 10.

Selenosulfonation of Unsaturated Cyclopropanes.

The radical selenosulfonation of vinylcyclopropanes is accompanied by ring-opening to give 1,5-addition products that afford 1-sulfonyl-2,4-dienes by selenoxide elimination (eq 11).12 Similar ring-opening is observed in cyclopropylidenes, whereas cyclopropylacetylene undergoes mainly 1,2-addition and provides the corresponding alkynic sulfone after selenoxide elimination (eq 12).12

Related Reagents.

Benzeneselenenyl Bromide; Benzeneselenenyl Chloride; Benzeneselenenyl Trifluoromethanesulfonate; Diphenyl Diselenide; N-Phenylselenophthalimide.

1. (a) Back, T. G. PS 1992, 67, 203. (b) Back, T. G.; Brunner, K.; Krishna, M. V.; Lai, E. K. Y.; Muralidharan, K. R. In Heteroatom Chemistry; Block, E., Ed.; VCH: New York, 1990; Chapter 4. (c) Simpkins, N. S. Sulphones in Organic Synthesis; Pergamon: Oxford, 1993; pp 22-26, 45-47, 82-83.
2. Back, T. G.; Collins, S.; Krishna, M. V. CJC 1987, 65, 38.
3. Gancarz, R. A.; Kice, J. L. JOC 1981, 46, 4899.
4. Back, T. G.; Collins, S. JOC 1981, 46, 3249.
5. Kice, J. L.; Kang, Y.-H. T 1985, 41, 4739.
6. Bäckvall, J.-E.; Nájera, C.; Yus, M. TL 1988, 29, 1445.
7. Chuang, C.-P. SC 1992, 22, 3151.
8. (a) Back, T. G.; Collins, S.; Kerr, R. G. JOC 1983, 48, 3077. (b) Back, T. G.; Collins, S.; Gokhale, U.; Law, K.-W. JOC 1983, 48, 4776. (c) Miura, T.; Kobayashi, M. CC 1982, 438.
9. Back, T. G.; Krishna, M. V.; Muralidharan, K. R. JOC 1989, 54, 4146.
10. (a) Back, T. G.; Collins, S.; Law, K.-W. CJC 1985, 63, 2313. (b) Back, T. G.; Krishna, M. V. JOC 1987, 52, 4265. (c) Back, T. G.; Collins, S.; Krishna, M. V.; Law, K.-W. JOC 1987, 52, 4258.
11. Back, T. G.; Lai, E. K. Y.; Muralidharan, K. R. JOC 1990, 55, 4595.
12. Back, T. G.; Muralidharan, K. R. JOC 1989, 54, 121.

Thomas G. Back

University of Calgary, Alberta, Canada

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