Novel synthesis of 2,6-benzothiazonine derivatives

The reaction of 1-alkylamino-1-alkylthio-3-phenyl-3-thioxopropenes with phthaloyl chloride in toluene at 60°C, followed by treatment with triethylamine, afforded 6-alkyl-3-phenyl-2,6-benzothiazonine-1,5,7-triones in good to excellent yields.