THIOSULFONIUM IONS - METHYLTHIOLATION OF THIOKETALS

Dimethyl(methylthio)sulfonium fluoroborate (1) and methanesulfenyl chloride (2) react rapidly with 2, 2-bis(methylt, hio)propane (5), 2, 2-dimethyl-l, 3-dithiolane (6), and 2, 2-dimethyl-l, 3-dithiane (7) in nitromethane or dichloromethane to cleave both thioketal carbon-sulfur bonds. A product of structure (CH3)2C(SCH3)X, X = Cl or S+(CH3)2, “BF4, was obtained from all three acetone thioketals together with methyl disulfide from 5 and polymer from 6 and 7. These reactions appear to involve thiosulfonium ion intermediates analogous to 1 that rearrange by cleavage and reformation of carbon-sulfur and sulfur-sulfur bonds. The 2-(methylthio)propyl cation](CH3)2C+(SCH3), 10] is evidently a common intermediate that is trapped by the nucleophile X to form the observed product. Reversible dissociation of this product results in its slow decomposition as the intermediate cation 10 reverts to thioketal 5 and other products. The behavior of a representative thioacetal, bis(2-methoxyethylthio)- methane, with 1 was comparable to that of thioketals with 1 and resulted in rupture of the thioacetal function by way of rearrangements involving C-S+ and S-S+ cleavage. © 1979, American Chemical Society. All rights reserved.