Nucleophilic displacement of 5-chloro-2-nitrobenzoic acid (I) with sodium sulfide produced thiol (II), which was further alkylated with dimethyl sulfate to furnish the methyl thioether (III). Nitro group reduction in (III) to yield 5-(methylthio)anthranilic acid (IV) was accomplished by treatment with hydrazine in the presence of FeCl3. The isatoic anhydride (V) was then prepared by treatment of anthranilic acid (IV) with either phosgene or ethyl chloroformate. Alkylation of benzoxazinedione (V) with iodomethane and NaH gave the N-methyl derivative (VI). The title compound was finally obtained by condensation of (VI) with the sodium enolate of malonic mono-amide (VII).

Nucleophilic displacement of 5-chloro-2-nitrobenzoic acid (I) with sodium sulfide produced thiol (II), which was further alkylated with dimethyl sulfate to furnish the methyl thioether (III). Nitro group reduction in (III) to yield 5-(methylthio)anthranilic acid (IV) was accomplished by treatment with hydrazine in the presence of FeCl3. The isatoic anhydride (V) was then prepared by treatment of anthranilic acid (IV) with either phosgene or ethyl chloroformate. Alkylation of benzoxazinedione (V) with iodomethane and NaH gave the N-methyl derivative (VI). The title compound was finally obtained by condensation of (VI) with the sodium enolate of malonic mono-amide (VII).