- SYNTHETIC AND MECHANISTIC ASPECTS OF SOME FREE-RADICAL AND ELECTROPHILIC ORGANOSELENIUM REACTIONS
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Selenenic derivatives such as selenosulfonates (PhSeSO2Ar) and selenenyl sulfonates (PhSeOSO2Ar) undergo free-radical and electrophilic additions to unsaturated organic substrates, often with high regio- and stereoselectivity.These processes can be employed in tandem with selenoxide eliminations, -sigmatropic rearrangements and various types of substitution and reduction reactions of the selenium moiety.Applications include preparations of various types of synthetically useful unsaturated sulfones and a new protocol for the synthesis of sterol side chains, such as that of the plant growth-promoter brassinolide.
- Back, Thomas G.
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p. 203 - 218
(2007/10/02)
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- Formation and Electrophilic Reactions of Benzeneselenenyl p-Toluenesulfonate. Perparation and Properties of Addition Products with Acetylenes
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Benzeneselenenyl p-toluenesulfonate (1) was generated in situ by the reaction of silver p-toluenesulfonate with benzeneselenenyl chloride in acetonitrile.The reagent reacted with acetylenes by electrophilic 1,2-addition to afford the β-(phenylseleno)vinyl p-toluenesulfonates 2-12, generally in high yield.The latter were formed preferentially by anti addition, but with poor regioselectivity, unless a strongly orienting group (e.g., phenyl) was present.Selenenyl sulfonate 1 was also unexpectedly produced via radical pathways by heating p-toluenesulfonic acid with AIBN in the presence of diphenyl diselenide, or from the pyrolysis of sulfinyl sulfone 15 with the diselenide.The regioisomeric adducts 3 and 4 were prepared from 1 and 1-decyne, and both underwent elimination with potassium tert-butoxide to afford the acetylenic selenide 19 initially, which isomerized to a 6:1 mixture of the propargylic and allenic selenides 20 and 21 upon further equilibration.A Fritsch-Buttenberg-Wiechell rearrangement is proposed for the elimination of 4.The syn elimination of the selenoxide of 4 required forcing conditions and afforded only ca. 20percent of the corresponding allenic sulfonate 22.The electrophile 1 induced the efficient cyclization of 5-hexen-1-ol and 4-pentenoic acid to the corresponding pyran 24 and lactone 25, respectively.It failed to cyclize alkynols, but afforded the lactones 28 and 29 from 4-pentynoic acid in low yield.
- Back, Thomas G.,Muralidharan, K. Raman
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p. 2781 - 2787
(2007/10/02)
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- Benzeneselenenyl p-toluenesulfonate: Formation and electrophilic addition to acetylenes
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The title compound 1 was produced in situ from PhSeCl and AgOSO2Ar (Ar = p-tolyl), and underwent electrophilic addition of acetylenes to afford adducts 2. The same products were unexpectedly formed from the reaction of ArSO3H and AIBN, or from the pyrolysis of ArS(O)SO2Ar, in the presence of acetylenes and PhSeSePh.
- Back,Muralidharan
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p. 1957 - 1960
(2007/10/02)
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