Selective synthesis of bis[1,2]dithiolo[1,4]thiazines from 4-isopropylamino-5-chloro-1,2-dithiole-3-ones

Reaction of 4-isopropylamino-5-chloro-1,2-dithiole-3-ones 3 and S₂Cl₂ in acetonitrile gave selectively 3-oxo-bis1,2]dithiolo1,4]thiazine-5-thiones 1 by the addition of triethylamine and bis1,2]dithiolo1,4]thiazine-3,5-diones 5 under the action of formic acid. 3,5-Diones 5 were also obtained by intramolecular cyclization of N,N-bis(5-chloro-3-oxo1,2]dithiol-4-yl)amines 6 with S₂Cl₂ in the presence of Et₃N.