Pyridine → Ethyl 2-methanesulfonamidothiazol-5-ylacetate

To a solution of ethyl 2-aminothiazol-5-ylacetate (32 g.) in methylene chloride (160 ml.) was added pyridine (27.2 g.) under ice-cooling, and to the mixture was dropwise added mesyl chloride (29.6 g.) in methylene chloride (29.6 ml.) over 30 minutes at 8° to 10° C. The mixture was further stirred for 8 hours at room temperature. After the reaction, methylene chloride was distilled off from the reaction mixture, and to the residue were added water (300 ml.) and ethyl acetate (300 ml.). The resulting mixture was adjusted to pH 2 with 10% hydrochloric acid under ice-cooling, and the precipitates were collected by filtration and washed with ethyl acetate. The precipitates were recrystallized from ethanol (600 ml.) to give ethyl 2-methanesulfonamidothiazol-5-ylacetate (27.3 g.), mp 153° to 155° C.