Synthesis and reactions of 1,4,2-dithiazines, bis(1,4,2-dithiazines) and 1,2,3-dithiazines by ring expansion of 1,3- or 1,2-dithiolium cations

Abstract

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 1,3dithiolium 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 nitrite 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.