Hydroxy-beta-thiolactams to oxazole-2-thiones. A novel DMSO-promoted oxidation.

3-Aryl-3-hydroxy-1-methylazetidine-2-thiones react with HCl in DMSO to give 3-methyl-5-aryloxazole-2-thiones. Substituent effects correlate with rate effects on hydrolyses of acetals of benzaldehyde. An (17)O labeling experiment indicates that the oxygen atom of the product is derived from the hydroxyl group. Trifluoroacetic anhydride/DMSO in CH2Cl2 can also promote the reaction. Mechanisms involving a Grob-type fragmentation of an activated substrate, followed by recyclization, or a cyclopropylcarbinyl type of rearrangement can account for this oxidative rearrangement.