Adducts of Phenoxathiin and Thianthrene Cation Radicals with Alkenes and Cycloalkenes

Abstract

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 (1)H and (13)C 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.

Addition of thianthrene cation radical to non-conjugated dienes—Part I: Addition to one double bond

“…Among these reactions, additions to alkenes and cycloalkenes, which were first discovered more than 20 years ago [15,16], have drawn, recently, further extensive interest [17][18][19][20]. Thus, whereas earlier [15][16][17] it was believed that addition of thianthrene cation radical perchlorate (Th •+ ClO − 4 ) to alkenes and cycloalkenes gave only bisadducts, it was found more recently that mono- (2) and bisadducts (3) are formed, in relative amounts depending on the structure of the alkene and cycloalkene [18][19][20]. Furthermore, it was found in these additions that the configuration of the alkene was retained in both types of adduct.…”

“…Furthermore, it was found in these additions that the configuration of the alkene was retained in both types of adduct. A mechanism of addition was formulated to explain these results [19,20] and is shown in scheme 1. The scheme shows that stereospecific cycloaddition of Th •+ to a double bond forms an intermediate, a cyclic distonic cation radical (1).…”

The role of aromatic groups in the Tobey–Simon additivity rule for vinylic protons

“…These data 11,12 have prompted us to look in the literature for aromatic groups that may also have an effect on cis and trans-vinylic protons opposite from that which is stated in the Tobey-Simon rule. We have collected data from the literature that are presented in Tables 1-5.…”

“…Recently, we have reported 1 H NMR data for five (E)-and 12 (Z)-5-thianthreniumylalkenes (4 and 5) 11 and of 14 (E)-and 11 (Z)-10-phenoxathiiniumylalkenes (6 and 7, Fig. 1).…”

“…The upfield shift of the cis proton in 5 and 7 was attributed to shielding by the heteroaromatic group, now orthogonal to, rather than coplanar with, the double bond; X-ray crystallographic data corroborating that orthogonal relationship was obtained. 11,12 With the use of Z gem (0. (8 and 9), which affects cis and trans protons equally.…”