Rearrangement reactions of Kopsins

Abstract

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.