Selective Syntheses of Bis[1,2]dithiolo[1,4]thiazines and Bis[1,2]dithiolopyrroles from Hünig's Base

The reaction of N,N-diisopropylethylamine (Hunig's base) and disulfur dichloride in 1,2-dichloroethane, in the presence of DABCO, gives 4-ethylbis[1,2]dithiolo[5,4-b][4‘,5‘-e][1,4]thiazine-3,5-dithione (1), or, by addition of oxygen donors, the 3-oxo-5-thione 2 or 3,5-dione 3 derivatives are selectively obtained. When the first reaction is performed in boiling chlorobenzene, 4-ethylbis[1,2]dithiolo[4,5-b][5‘,4‘-d]pyrrole-3,5-dithione (4) is obtained by sulfur extrusion from 1, and in the presence of oxygen donors, the 3-oxo-5-thione 5 or 3,5-dione 6 derivatives are selectively obtained. Some interconversions of compounds 1−6 are described, and a coherent set of reaction pathways for the formation of all six products is proposed. X-ray diffraction shows that the new bis-dithiolothiazine ring system of 1−3 is folded out of planarity about the thiazine N−S vector, with the N-ethyl group folded back over the thiazine ring in a scorpion-like conformation. The new bis-dithiolopyrrole ring system of 4−6 is plana...