Synthesis of 2,3-Dimethoxy-7-methyl-7,12-dihydro-6H-[1]-benzofuro-[2,3-c]-[1]-benzazepin-6,12-dione

Treatment of 5,6-dimethoxy-2-(methylphenylcarbamoyl)-benzofuran-3-carboxylic acid with PPA yielded 2,3-dimethoxy-7-methyl-7,12-dihydro-6H-[1]-benzofuro-[2,3-c]-[1]-benzazepin-6,12-dione. The analogous 2-[(5,6-dimethoxybenzofuran-2-carbonyl)methylamino]benzoic acid was resistant to cyclization, whereas 2-[(6-methoxybenzofuran-2-carbonyl)-amino]benzoic acid underwent cyclization to the corresponding 3,1-benzoxazin-4-one.