Abstract
Novel pyrolysis reactions of 4-isoxazolin-3-thiones (X) are described, affording two regioisomeric 1, 4-dithiins (III, IV) and thioacetamides (XI). Among the thioacetamides, N-methylbenzoylthioacetamide (XIe) was identical with an authentic sample prepared by the reduction of 2-methyl-5-phenyl-4-isoxazolin-3-thione (Xe) with thiophenol. The structures of the dithiins were deduced from the physicochemical data, especially the shielding and deshielding effects in the NMR spectra. A mechanism for the reactions is proposed by analogy with the thermal isomerization of 3-isoxazolones into 2-oxazolones. In order to account for the formation of the isomeric dithiins, a thiirene intermediate (II) was assumed to be involved in the reaction pathway.