Unexpected formation of a 10H-Pyrido[2,3-h]pyrazolo[3,4-b]quinoline derivative,a new ring system

Treatment of N-(1,3-dimethylpyrazol-5-yl)-4-anthranilic acid with phosphorus oxychloride gave an intermediate which was condensed with 3-dimethylaminopropylamine to yield 10,8-dimethyl-7-(3-dimethylaminopropylamino)-10H-pyrido2,3-h]pyrazolo3,4-b]quinoline (IV). The structure of IV, which represents a previously undescribed ring system, was confirmed by an independent synthesis.