Chemical Transformation of Protoberberines. XIV. : Acid-Catalyzed Cleavage of 8-Alkyl-8,14-cycloberbines. A Simple Method for the Preparation of N-Unsubstituted Spirobenzylisoquinolines(Organic,Chemical)
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On treatment with an acid, 8-alkyI-8,14-cyeioberbines (9) afforded the N-unsubstituted spirobenzylisoquinolines (10, 11, and 12) through regioselective C_8-N bond cleavage in contrast to the 8-unsubstituted 8,14-cycloberbine (9d), which gave the benzindenoazepine (19, R=H) through regioselective C_<14>-N bond cleavage. Reduction of 9 with NaBH_4 or LiAlH(OBu')_3 yielded stereoselectively the alcohol (20 or 21, respectively) as the main product. Acidic treatment of the isomeric alcohols (20 and 21) effected regioseiective C_8-N bond cleavage, resulting in thc N-unsubstitutcd spirobenzylisoquinolines (22-26).