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

Abstract

Four examples of the chiral thiazolidin-2-one 1,1-dioxides 5 have been prepared by reaction of the appropriate amino alcohols 11 with CS₂ in aqueous 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 °C, 5a–c decompose mainly by loss of SO₂ 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 CO₂ 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 ¹³C NMR spectra are presented for 5, 12 and 13 and the ³³S NMR spectrum has been obtained for 5c.