The Condensation of Isatin with o-Phenylenediamine

Article abstract of DOI:10.1246/bcsj.55.2293

The condensation of isatin with o-phenylenediamine has been studied in various kind of solvents.The reaction gave pure indolo<2,3-b>quinoxaline (1) in acidic solvents, while it gave a mixture containing at least two out three compounds, 1, an anil and a spiro compound, in neutral or basic organic solvents.The anil and spiro compounds were converted to 1 in the presence of acid or by heating them above their melting points.The mechanism of the formation of these compounds and the conversion could be explained by the presence of the intermediate of the adduct formed between the amino groups of o-phenylenediamine and the β-carbonyl of isatin.