The compound, (3-oxo-5H-thiazolo[2,3-b]quinazolin-2(3H)-ylidene)acetic acid (compound IIIa), triethylamine, and N-(tert-butyl)benzylamine, in relative molar amounts of 1, 2, and 1, respectively, are dissolved in dichloromethane, and the solution is cooled to 10° C. The compound, N,N-bis(2-oxo-3-oxazolidinyl)phosphorodiamidic chloride, (relative molar amount, 1) is added to the reaction mixture, which is then stirred at about 25° C. for about 2 hours. Following acidification with dilute hydrochloric acid, the reaction mixture is filtered, and the organic phase is washed with water, dried over anhydrous magnesium sulfate, and evaporated to dryness under reduced pressure, leaving the N-tert-butyl-N-benzyl(3-oxo-5H-thiazolo[2,3-b]quinazolin-2(3H)-ylidene)acetamide as a solid. The N-tert-butyl-N-benzyl(3-oxo-5H-thiazolo[2,3-b]quinazolin-2(3H)-ylidene)acetamide (compound VI) is then recrystallized from anhydrous ethanol. Replacement of (3-oxo-5H-thiazolo[2,3-b]2(3H)-ylidene)acetic acid with a derivative thereof in which a nuclear hydrogen of the benzene ring has been substituted with lower alkyl, alkoxy, halogen, trifluoromethyl, NO2 or NH2, results in the formation of the corresponding derivative of N-tert-butyl-N-benzyl(3-oxo-5H-thiazolo[2,3-b]quinazolin-2(3H)-ylidene)acetamide.
