Conversion of imino-1,2,3-dithiazoles into 2-cyanobenzothiazoles, cyanoimidoyl chlorides and diatomic sulfur

Primary aromatic amines condense with 4,5-dichloro-1,2,3-dithiazolium chloride 1 to give high yields of the N-aryl imines 2 which on heating give 2-cyanobenzothiazoles 3, thus providing a simple two-step route to these heterocycles from the appropriate aniline. This thermolysis is favoured by electron donating substituents in the aniline ring, and retarded by electron withdrawing groups in favour of a second pathway in which both dithiazole sulfur atoms are lost to form cyanoimidoyl chlorides 4. This is the sole pathway when both aniline ortho positions are substituted. Analogous N-alkyl imines 5, prepared from the salt 1 and the bis(trimethylsilyl) derivatives of the amine, also decompose with loss of both sulfur atoms as singlet diatomic sulfur, S2. 4-Chloro-5-methylimino-5H-1,2,3-diathiazole 5a does this at 140–150 °C and the S2 generated is intercepted with 2,3-diphenylbutadiene, 2,3-dimethylbutadiene and norbornene to give 16a, 16b and 17 respectively.