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

Abstract

Abstract Reactions of 2 H ‐3,1‐benzoxazine‐2,4‐(1 H )dione (isatoic anhydride) (1) with anions of 1,4‐dihydro‐5 H ‐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) .