A solution of (3-oxo-5H-thiazolo[2,3-b]quinazolin-2(3H)-ylidene)acetic acid (1.3 g, 5 mmols), triethylamine (1.5 ml, 0.01 mol), and N-(tert-butyl)benzylamine (0.93 ml, 5 mmols) in 10 ml dichloromethane, was cooled to 10° C. Then, 1.27 g (5 mmols) of N,N-bis(2-oxo-3-oxazolidinyl)phosphorodiamidic chloride was added, and the reaction mixture was stirred at room temperature for 20 hours. Following acidification with dilute hydrochloric acid, the reaction mixture was filtered and the organic layer was washed with water, dried over anhydrous magnesium sulfate, and evaporated to dryness under reduced pressure leaving an orange-yellow solid which was recrystallized from anhydrous ethanol. Yield--0.71 g. Mp 195°-197° C.
