Dithia cyclic compounds

Intramolecular S. S (2a/la ) three-electron bonded radical cations The steric parameter becomes even more pronounced, and in fact dominant, for radical cations with intramolecular sulfur-sulfur coupling. Most examples, studied by radiation chemical (but also other) methods, have been observed in the oxidation of cyclic and open chain dithia compounds.84,85,117- 23 xhe two extreme situations with respect to the most (left) and least favorable (right) orbital alignment are depicted in Figure 3. The former is closest realized upon one-electron oxidation of 1,5-dithiacyclooctane, 6, and was first described in conventional ESR work by W. K. Musker.l 19-121 jt exhibits an optical absorption with 400 nm and, incidentally, consti-... 

Literature on the stability of individual cydk disulfides covers (i) compounds that polymerize on standing like 3,3-dimethyl-1 -dithiolaiK [124,12, 3-hydroxy-l,2-dithiolane [126] and iV-phenyl-4-oxo-5-aza-l,2-dithia-cyclohexane [127,128] ii) compoimds which polymerizes on heating such as dibenzo-lA5,6-tetrathiocin [129] and iii) compounds that polymeixK in neat form when a catalyst is added, such as cis-l,2-dithiacyclohex-4-aie [130] and l-oxa-4,5-dithiacycloheptane [13, 119, 130]. Detailed study of the stability of cyclic disulfides towards polymerization revealed that 1,2-dithiai are the only class of simple cyclic disulfides that is thermodynamically staUe with respect to its polymerization in the melt or as concentrated solutions [131]. 

Synthesis and Properties.—The two most general methods for preparing sulphonium ylides continue to be a-deprotonation of a sulphonium salt and the reaction of a sulphide (or disulphide with a carbene. A new development involves the reaction of the thianthrene or phenoxathiin cation radical with a dicarbonyl compound, e.g. ethyl benzoylacetate, to give (4). An infrequently used but useful route to sulphonium ylides involves reaction of sulphides e.g. dithia[3,3]cyclophanes with benzyne. A detailed description of a preparation of the sulphonium salt precursor to Trost s diphenylsulphonium cyclopropylide has appeared. The selectivity of ylide formation in the reaction of cyclic and acyclic sulphides with carbenes has been examined and compared with the much... 

---