Substituted 1,4,2-dithiazines: synthesis by ring expansion of 1,3-dithiolium cations, solution redox properties and X-ray crystal structures of a monocyclic and a bicyclic derivative

Abstract

A range of derivatives of the 8 π-electron 1,4,2-dithiazine system, viz. compounds 11a–d and 19–24, have been synthesised by ring expansion of the corresponding 1,3-dithiolium salts 8a–d and 13–18, respectively, using a mixture of iodine and aqueous ammonia at room temperature. A mechanism is proposed for the reaction. Competing reaction of compound 14 yields the imine 26 as a minor product. Single crystal X-ray analyses of compounds 11a and 23 reveal that the 1,4,2-dithiazine ring adopts a boat conformation with fold angles about the S ⋯ S axis of 50 and 48°, respectively. The 1,4,2-dithiazine heterocycle is oxidised electrochemically to yield the cation radical at E₁^½ca. 1.0–1.2 V (versus Ag/AgCl); some derivatives are further oxidised to the dication at E₂^oxca. 1.4–1.7 V.