SYNTHESIS AND REACTIONS OF 1,4,2-DITHIAZINES, BIS(1,4,2-DITHIAZINES) AND 1,2,3-DITHIAZINES BY RING EXPANSION OF 1,3-DITHIOLIUM OR 1,2-DITHIOLIUM CATIONS

5,6-Dimethyl-3-(2-thienyl)-1,4,2-dithiazine 6, and 3,3'-(meta- and para-phenylene) bis(5,6-dimethyl-1,4,2-dithiazines) 10 and 12 have been synthesised, by reaction of the corresponding 1,3-dithiolium or bis(1,3-dithiolium) salts, 5, 9 and 11. with a mixture of iodine and aqueous ammonia. A range of the 1,4,2-dithiazine derivatives have been desulfurised to yield isothiazoles upon thermolysis in refluxing toluene. Photolysis of the 1,4,2-dithiazines in the presence of dimethyl acetylenedicarboxylate. tetracyanoethylene and norbornene gives Diels-Alder adducts of the intermediate 1,2-dithiones, and nitrile fragments. Grignard reagents react at S-1 of the 1,4,2-dithiazines, fragmenting the ring to afford nitrile and 1,2-dithioethene moieties. The 1,2,3-dithiazine derivatives 28 and 31 have been isolated from the reaction of the 1,2-dithiolium salts with a mixture of iodine and ammonia; desulfurisation of the 1,2,3-dithiazines occurs readily at room temperature to yield isothiazoles.