Mono- and Bisadducts from the Addition of Thianthrene Cation Radical Salts to Cycloalkenes and Alkenes

Abstract

Thianthrene cation radical salts, Th(*)(+) X(-)(X(-) = a, ClO(4)(-); b, PF(6)(-); c, SbF(6)(-)), add to cycloalkenes (C(5)-C(8)) in acetonitrile (MeCN) to form 1,2-bis(5-thianthreniumyl)cycloalkane salts and 1,2-(5,10-thianthreniumdiyl)cycloalkane salts, most of which have now been isolated and characterized. These are called bis- (3, 6, 9, 12) and monoadducts (4, 7, 10, 13). The proportional amount of the monoadduct obtained in the initial stage of the reaction varied with the cycloalkene in the order C(6) << C(5) < C(7) << C(8). Thus, the ratio bis:mono for C(5) and C(7) was, respectively, about 80/20 and 50/50. In contrast, only about 5% of the C(6) monoadduct (7a) and none of 7b,c was obtained, while for C(8) none of the bisadducts 12a-c was found. Bisadducts 3 and 9 lost thianthrene (Th) slowly in MeCN solution and changed into monoadducts 4 and 10. A comparable change from 6a into 7a was not observed. The monoadducts, themselves, lost a proton slowly in dry MeCN and opened into 1-(5-thianthreniumyl)cycloalkenes (5, 8, 11, 14). With 3 and 9, particularly, it was possible to follow with NMR spectroscopy the succession of changes, for example, 3 to 4 to 5. The opening of a monoadduct was made faster by adding a small amount of water to the solution. The bisadducts of 4-methylcyclohexene (15a) and 1,5-cyclooctadiene (17a) were isolated and characterized. Although a small amount of monodduct (16a) of 4-methylcyclohexene was found with NMR spectroscopy, it could not be isolated. Bis- and monoadducts were obtained also in additions of Th(*)(+) ClO(4)(-) to acyclic alkenes, in relative amounts that, again, varied with the alkene. From cis-2-butene the dominant product was the bisadduct (18), while the monoaduct (19) was characterized with NMR spectroscopy but could not be isolated. In contrast, trans-3-hexene gave mainly the monoadduct (21), while the bis adduct (20) could not be isolated. With 4-methyl-cis-2-pentene, both bis- (22) and monoadduct (23) were isolated, the former being dominant. The conversion of 18 into 19 was characterized with NMR spectroscopy. In all cycloalkene bisadducts, the configurational relationship of the two thianthrenium groups was trans, while in the monoadducts, the bonds to the single thianthrene dication were (necessarily) cis. In both bis- and monoadducts of acyclic alkenes, the configuration of the alkene was retained. The mechanisms of addition with retention of configuration, of conversion of a bis- into a monoadduct, and of opening of a monoadduct are discussed. Products were identified with a combination of NMR spectroscopy, X-ray crystallography, elemental analysis, and (for cycloalkene adducts) reaction with thiophenoxide ion.

Addition of thianthrene cation radical to non-conjugated dienes—Part II: Addition to two double bonds

“…The bisadduct dihexafluorophosphate (16) of 1,4-cyclohexadiene was characterized with NMR spectroscopy and X-ray crystallography; and its Ortep diagram is shown in figure 1. Figure 1 shows the trans relationship of the two thianthreniumyl groups in 16, a feature that was seen earlier with the bisadduct of 1,5-cyclooctadiene [3]. There was no evidence for formation of a monoadduct (with structure such as that in 13) from these two cyclic dienes.…”

“…It was Reaction of a large excess of Th •+ with 1,4-cyclohexadiene and 1,5-cyclooctadiene failed to give addition to more than one double bond. From each of these dienes, only a bisadduct was obtained, one of which (of 1,5-cyclooctadiene) has been reported earlier [3], too. The bisadduct dihexafluorophosphate (16) of 1,4-cyclohexadiene was characterized with NMR spectroscopy and X-ray crystallography; and its Ortep diagram is shown in figure 1.…”

“…Under the conditions of reaction, namely, a large molar excess of diene over Th •+ or even a molar ratio diene: Th •+ of 1:2, addition occurred to only one of the diene's double bonds. That is, the diene behaved as an alkene and addition of Th •+ gave the now well-documented mixture of bis-and monoadduct [2][3][4]. The mechanism of the formation of these two adducts has been laid out in Part I.…”

“…The mechanism of the formation of these two adducts has been laid out in Part I. It was pointed out that hitherto only one diene, 1,5-cyclooctadiene, had been used in reactions with Th •+ and that one of that diene's double bonds had suffered addition, to give a bisadduct [3]. As a continuation of the work described in Part I, we set out to find if, in reactions with a large excess of Th •+ , both of the double bonds of acyclic and cyclic non-conjugated dienes would participate in additions.…”

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.…”