| Abstract
| - Addition of phenoxathiin cation radical (PO•+) to acyclic alkenes in acetonitrile (MeCN) solution occurredstereospecifically to form bis(10-phenoxathiiniumyl)alkane adducts. Stereospecific trans addition is ascribedto the intermediacy of an episulfonium cation radical. The alkenes used were cis- and trans-2-butene,cis- and trans-2-pentene, cis- and trans-4-methyl-2-pentene, cis- and trans-4-octene, trans-3-hexene, trans-3-octene, trans-5-decene, cis-2-hexene, and cis-2-heptene. The erythro bisadducts (compounds 6) wereobtained with trans-alkenes, while threo bisadducts (compounds 7) were obtained with cis-alkenes. Theassigned structures of 6 and 7 were consistent with their NMR spectra and, in one case, 6c (the adductof trans-4-methyl-2-pentene) was confirmed with X-ray crystallography. Additions of PO•+ to 1,4-hexa-,1,5-hexa-, 1,6-hepta-, and 1,7-octadiene gave bis(10-phenoxathiiniumyl)alkenes (compounds 8), theassigned structures of which were consistent with their NMR spectra. Each of these adducts lost a protonand phenoxathiin (PO) when treated with basic alumina in MeCN solution. Compounds 6 (from trans-alkenes) gave mixtures of (Z)- (9) and (E)-(10-phenoxathiiniumyl)alkenes (10) in which the (Z)-isomers(9) were dominant. On the other hand, compounds 7 (from cis-alkenes) gave mixtures of 9 and 10 inwhich, with one exception (the adduct 7c of cis-4-methyl-2-pentene), compounds 10 were dominant.The path to elimination is discussed. The alkenes 9 and 10 were characterized with NMR spectroscopyand, in one case (9a), with X-ray crystallography. Reactions of 8b−d with basic alumina gave mixturesof (E)- (13) and (Z)-(10-phenoxathiiniumyl)dienes (14), in which compounds 13 were dominant. Theconfiguration of the product from 8a (the adduct of 1,4-hexadiene) could not be settled. Noteworthyfeatures in the coupling patterns and chemical shifts in the NMR spectra of some of the adducts and theirproducts are discussed and related to adduct conformations.
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