Synthesis of bis[1,2]dithiolo[1,4]thiazines and a [1,2]dithiolo[1,4]thiazine from tertiary diisopropylamines

The reaction of N-(2-chloroethyl)diisopropylamine 1a with S2Cl2 allows the selective one-pot preparation of the tricyclic 4-(2-chloroethyl) bisdithiolothiazines 2-4 or, by addition of phosphorus pentasulfide at a late stage in the reaction, of the dithiolothiazine 5. The chloroethyl derivative 2 is also obtained from (2-diisopropylamino)ethanethiol 1b, or its disulfide 1c, with S2Cl2, in a rare conversion of a thiol or disulfide into the corresponding chloro compound. Compounds 2 and 5 are also obtained from N-(2-hydroxyethyl)diisopropylamine 1d, though in much lower yields. The reaction of N-(2-phenylthioethyl) (1e) or N-(2-phthalimidoethyl)diisopropylamines 1f,g affords bisdithiolothiazines 7, 8, 9, and 11 and the dithiolopyrrole 10. A coherent set of reaction pathways for the formation of these products is proposed. X-ray crystallography shows that the bisdithiolothiazine ring system of 2 is folded out of planarity about the thiazine N-S vector, with the N-chloroethyl group folded back over the thiazine ring with the chlorine atom lying above the thiazine sulfur atom; the dithiolothiazine ring system of 5 has the thiazine ring in a "sofa" conformation.