Reactions of tetracyanoethylene oxide with 1,2,3-dithiazoles

Abstract

In the synthesis of dicyanomethylene-1,2,3-dithiazole 2 from dithiazolethione 1 and tetracyanoethylene oxide (TCNEO), formation of the thione-oxide (sulfine) 3 becomes competitive under mild conditions, in the first transfer of oxygen from TCNEO to a thione group. Thione 1 is converted into sulfine 3 in high yield by the usual oxidant, m-chloroperbenzoic acid. An isomeric pair of unusual enimino-dithiazoles, 7 and 8, are minor by-products in the synthesis of the dicyanomethylene compound 2 from TCNEO and 4,5-dichloro-1,2,3-dithiazolium chloride 6; it is proposed that their formation derives from the ring opened stabilised ylide form of TCNEO acting as a nucleophile through nitrogen 9b, as well as through carbon 9a. The reaction of salt 6 and TCNEO in the presence of N-chlorosuccinimide yields the oxidised acyliminodithiazole 11 which has been synthesised independently from 6 and dichlorocyanoacetamide 12. Trichloroacetamide reacts with 6 to give the analogous imine 13 which is incorrectly assigned the fused bicyclic structure 14 in the patent literature.