Adducts of Phenoxathiin and Thianthrene Cation Radicals with Alkenes and Cycloalkenes

Phenoxathiin cation radical perchlorate (PO•+ClO4-) added stereospecifically to cyclopentene,
cyclohexene, cycloheptene, and 1,5-cyclooctadiene to give 1,2-bis(5-phenoxathiiniumyl)cycloalkane
diperchlorates (4−7) in good yield. The diaxial configuration of the PO+ groups was confirmed with
X-ray crystallography. Unlike additions of thianthrene cation radical perchlorate (Th•+ClO4-) to
these cycloalkenes, no evidence for formation of monoadducts was found in the reactions of
PO•+ClO4-. This difference is discussed. Addition of Th•+ClO4- to five trans alkenes (2-butene,
2-pentene, 4-methyl-2-pentene, 3-octene, 5-decene) and four cis alkenes (2-pentene, 2-hexene,
2-heptene, 5-decene) gave in each case a mixture of mono- and bisadducts in which the configuration
of the alkene was retained. Thus, cis alkenes gave erythro monoadducts and threo bisadducts,
whereas trans alkenes gave threo monoadducts and erythro bisadducts. In these additions to
alkenes, cis alkenes gave predominantly bisadducts, while trans alkenes (except for trans-2-butene)
gave predominantly monoadducts. This difference is explained. 1,2-Bis(5-phenoxathiiniumyl)cycloalkanes (4−7) and 1,2-bis(5-thianthreniumyl)cycloalkanes underwent fast elimination reactions
on activated alumina forming, respectively, 1-(5-phenoxathiiniumyl)cycloalkenes (8−11) and 1-(5-thianthreniumyl)cycloalkenes (12−16). Among adducts of Th•+ClO4- and alkenes, monoadducts
underwent fast ring opening on alumina to give (5-thianthreniumyl)alkenes, while bisadducts
underwent fast eliminations of H+ and thianthrene (Th) to give (5-thianthreniumyl)alkenes also.
Ring opening of monoadducts was a stereospecific reaction in which the configuration of the original
alkene was retained. Thus, erythro monoadducts (from cis alkenes) gave (E)-(5-thianthreniumyl)alkenes and threo monoadducts (from trans alkenes) gave (Z)-(5-thianthreniumyl)alkenes. Among
bisadducts, elimination of a proton and Th occurred and was more complex, giving both (E)- and
(Z)-(5-thianthreniumyl)alkenes. These results are explained. Configurations of adducts and
(5-thianthreniumyl)alkenes were deduced with the aid of X-ray crystallography and 1H and 13C
NMR spectroscopy. In the NMR spectra of (E)- and (Z)-(5-thianthreniumyl)alkenes, the alkenyl
proton of Z isomers always appeared at a lower field (0.8−1.0 ppm) than that of E isomers.