Answer: In a complex sequence of about 15 reaction steps, N-ethyl di-isopropylamine (Hünig's base) reacts with disulfur dichloride (sulfur monochloride) to give the bis([1,2]dithiolo)-[1,4]thiazine (Sscorpionine) in an overall yield of 40%. Remarkable features of this reaction are
If the carbon connectivity of Hünig's base is retained, only a few reasonable structures are possible for such a stable compound, and spectroscopy indicated the structure shown for Sscorpionine to the right, which was confirmed by X-ray crystallography.
If the reaction is run in the presence of an oxygen source (e.g. formic acid or THF!), two other products are also formed, with one or both of the thione sulfur atoms replaced by oxygen. All three products (which have been interconverted) have very similar shapes and conformations in the crystal lattice. The delocalised dithiole rings are planar, with the fused ring system folded about the thiazine N...S axis, and with the N-ethyl group folder back, scorpion-like, towards the thiazine ring sulphur. Details can be found in Angew. Chemie, 1997, 36, 281 where a mechanism is proposed for the reaction. This compound and its analogues are displaying some very interesting chemistry.
Details can be found in Angew. Chemie, 1997, 36, 281 where a mechanism is proposed for the reaction. This compound and its analogues are displaying some very interesting chemistry.