ハロスルホン酸を閉環剤とするイソキノリン合成(第2報)クロルスルホン酸中3,4-ジメトキシベンジリデンアミノアセタールの閉環によるイソキノリン誘導体の生成

抄録

In the course of a study on the isoquinoline synthesis in which halosulfonic acid was employed as a cyclizing agent, 3, 4-dimethoxybenzylideneaminoacetal (4) was treated with chlorosulfonic acid at -5°, followed by standing at a room temperature for 72 hr to afford two bases, 3-chloro-6, 7-dimethoxyisoquinoline (7), mp 134-135° (hydrochloride, mp 158-162° (decomp.)) in 53% yield and a very small amount of 6, 7-dimethoxyiso-quinoline (12). The former is a new compound whose structure was determined from various spectral data and by degradative evidence including its reduction to 6, 7-dimethoxy-1, 2, 3, 4-tetrahydroisoquinoline hydrochloride (8) and its oxidation to a new acid, 6-chlorocinchomeronic acid (10), mp 191-193°. Formation of 12 was recognized by means of thin-layer chromatography (TLC) and gas-liquid chromatography (GLC) identical with those of an authentic sample.