4-Bis(methylthio)methylene-2-phenyloxazol-5-one: Template for Oxazoles

Significance

The conversion of ketene thioacetals A into diversely substituted oxazoles is reported. The starting material is easily prepared in three steps from the reaction of an amino acid with ethyl chloroformate, CS₂, and dimethyl sulfate in 61% yield. These thioacetals are treated with nucleophiles to yield acyclic compounds, which under various conditions, most prominently using silver carbonate, undergo ring closure to yield substitu­ted oxazoles. The substrate scope was very well studied in terms of the nucleophiles, but only hippuric acid was used as the starting amino acid. The yields range from good to excellent and the further transformations of the resulting oxazoles were also studied (dethiomethylation, C-N coupling).