H ünig's base and S 2 Cl 2 give the fused 1,4-thiazines 1 and (in the presence of formic acid) 2 and 3, each of which readily extrudes sulfur, selectively and quantitatively, to give the fused pyrroles 4, 5 and 6 respectively; at higher temperatures H ünig's base and S 2 Cl 2 can be converted into the pyrroles in one pot, and the cycloadducts 8 and 10 are thus readily available in two steps.

The reaction of N,N-diisopropylethylamine (Hünig'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 planar and extensively delocalized.

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The reaction of N-(2-chloroethyl)diisopropylamine 1a with S 2 Cl 2 allows the selective one-pot preparation of the tricyclic 4-(2-chloroethyl)bisdithiolothiazines 8 and 9 or, by addition of phosphorus pentasulfide at a late stage of the reaction, of the dithiolothiazine 6b characterised by X-ray crystallography; the chloroethyl derivative 8 is also obtained from (2-diisopropylamino)ethanethiol 1b and its disulfide 1c and S 2 Cl 2 , in a rare conversion of a thiol or disulfide into the corresponding chloro compound.

The first multicomponent coupling of isocyanides, α,β-unsaturated carbonylic compounds and dienophiles, based on the trapping of unstable intermediate 2-aminofurans, is described. This novel tandem [4 + 1]-[4 + 2] cycloaddition is efficiently catalysed by yttrium triflate and constitutes an operationally simple and highly convergent approach to a variety of polysubstituted anilines. Moreover, this methodology permits the use of tert-butylisocyanide as a convertible isocyanide to yield directly N-unprotected anilines in the same pot.