Reactions of 2H‐3,1‐benzoxazine‐2,4‐(1H)dione (isatoic anhydride) with anions of 1,4‐dihydro‐5H‐pyrazol‐5‐ones: Synthesis of pyrazolo[5,1‐b]quinazolin‐9‐ones

Reactions of 2H-3,1-benzoxazine-2,4-(1H)dione (isatoic anhydride) (1) with anions of 1,4-dihydro-5H-pyrazol-5-ones (2) gave pyrazolo[5,1-6]quinazolin-9-ones (3) via the nucleophilic attack of the anion 2b rather than 2a. However, in the case of 5-methoxyisatoic anhydride (10c), both products 3e and 11c were obtained. A new synthetic method of preparation of 5-(alkylthio)-2-aminobenzoic acids (18) was described. These acids (18) were used to synthesize a series of substituted pyrazolo[5,1-b]quinazolin-9-ones (3).