DESULFURIZATION OF EPIDITHIODIOXOPIPERAZINES - MECHANISTIC AND CHIROPTICAL STUDY

The stereochemical course of the desulfurization reaction of the epidithiodioxopiperazine 6 with (C6H5)3P has been studied. The resulting monosulfide 7 has inverted chirality at the bridgehead carbon atoms, as has been established by X-ray analysis. In addition, a novel method is described for the determination of the stereochemistry of this reaction. It is based upon 1H NMR spectroscopy in the presence of a chiral shift reagent. As the sign of the CD curves of 6 and 7 and the corresponding tri-and tetrasulfides 8 and 9 correlates with the configuration of the bridgehead carbon atoms, it is, at least for these epi(poly)-thiodioxopiperazines, a good criterion for their absolute configuration. A mechanism for the desulfurization is proposed, in which the phosphine attacks regiospecifically sulfur atom 3 of compound 6, followed by an epimerization of carbon atom C9athrough a thiocarbonyl intermediate (Scheme I, pathway II). © 1979, American Chemical Society. All rights reserved.