Umlagerungsreaktionen des Kopsins

Kopsine (I) undergoes a reversible acyloin rearrangement to isokopsine (111) under acid catalysis or preferably by the action of heat. On alkaline treatment both bases undergo N‐decarbomethoxylation to give the same mixture of decarbomethoxy‐kopsine (IX) and decarbomethoxy‐isokopsine (V). IV and V are easily interconvertible by action of acid, base or heat. Reduction of isokopsine (111) by sodium borohydride followed by decarbomethoxylation leads to decarbomethoxy‐dihydro‐isokopsine (XIII) also obtained by borohydride reduction of V. A similar reduction of IV leads to two epimeric alcohols, VII and X, which are respectively formed by alkaline hydrolysis of dihydrokopsines‐A (VI) and B (IX). Indications have been obtained for the occurrence in the dried leaves of Kopsia fruticosa of IV and V from both of which fruticosine is different.