Cyclization of N-acylanthranilic acids with Vilsmeier reagents. Chemical and structural studies

Vilsmeier reagents, generated from e.g. N, N-dimethylformamide and oxalyl chloride, react with N-acetylanthranilic acid to produce the 2-(2'-dimethylamino)ethenyl-4H-3,1-benzoxazin-4-one 13a.. N-phenylacetylanthranilic acid similarly gave 2-(2'-dimethylamino-1'-phenyl)ethenyl-4H-3, 1-benzoxazin-4-one 6a, whose structure has been determined by X-ray crystallography. The benzoxazinone 6a could readily be converted to fused heterocyclic systems, thus e.g. 13a and hydrazine hydrate gave pyrazolo[5,1-b]-4H-quinazoline 20a. Reaction of N-acetylated anthranilic acids and oxalyl chloride alone gave the fused oxazolidine-4,5-diones 24. The structure of one representative, 24a, was established by X-ray crystallography. Thermolysis of 24a gave, after elimination of CO+CO2, 2-benzyl-4H-3,1-benzoxazin-4-one 7 in quantitative yield.