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

A range of derivatives of the 8 pi-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 11 a 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-degrees, respectively. The 1,4,2-dithiazine heterocycle is oxidised electrochemically to yield the cation radical at E1(1/2) ca. 1.0-1.2 V (versus Ag/AgCl); some derivatives are further oxidised to the dication at E2ox ca. 1.4-1.7 V.