Synthesis and pyrolytic behaviour of thiazolidin-2-one 1,1-dioxides

Four examples of the chiral thiazolidin-2-one 1,1-dioxides 5 have been prepared by reaction of the appropriate amino alcohols If with CS, inaqueous sodium hydroxide to give the thiazolidine-2-thiones 12, followed by oxidation with KMnO4 under phase-transfer conditions in the presence of benzoic acid, either directly or via the thiazolidin-2-ones 13. Upon flash vacuum pyrolysis (FVP) at 650 degrees C, 5a-c decompose mainly by loss of SO, to give an alkene and benzyl isocyanate together with other products from fragmentation of the N-benzyl group, A significant:minor pathway involves net loss of CO, and water to give the 2-phenyl-4,5-dihydrothiazoles 21 together with their aromatisation products 22 and 23, A mechanism for this new heterocyclic transformation is proposed involving initial expansion to a cyclic carbamic-sulfinic anhydride (2,1,4-oxathiazin-3-one-1-oxide). The fully assigned C-13 NMR spectra are presented for 5, 12 and 13 and the S-33 NMR spectrum has been obtained for 5c.