58 イソキノリンアルカロイドの合成研究

抄録

Conceptually new schemes of synthesis of isoquinoline alkaloids are introduced, in connection with studies of the electrophilic substitution reaction on phenethylamine derivatives. The spiroketone V, a key intermediate, was synthesized from N-acetyl 3,4-dimethoxyphenethylamine by several steps. Base treatment of V produced the indene VI, which possessed the 3-benzazepine moiety characteristic of the rhoeadine alkaloid, fused in the correct manner to a potential CD system with the desired substitution paterns. Base-catalyzed oxidation of VI (Triton B in pyridine-molecular oxygen) afforded the bright red indenone VII, which on Rose Bengal sensitized photooxygenation yielded the ketolactone VIII. Sodium borohydride reduction of VIII followed by dilute hydrochloric acid treatment produced the cis-lactone IX. Subsequent reduction with diisobutylaluminum hydride and methylation led to the total synthesis of (±) cis-alpinine XI. Interaction of XIIa,b, obtained by hydrolysis of Va,b, with bromine yielded the bromides whose treatment with tryethylamine afforded the spiroketones XIIIa,b, respectively. Similar conversions with VIIa,b led to XVa,b, by way of XIVa,b, respectively. XIIIb had previously been converted to the ochotensimine. Thus a new total synthesis of ochotensimine has been achieved. The scheme to provide XVa,b promises to lead to a very convenient route to the ochrobirine type of alkaloid. A study on synthesis of the phthalide isoquinoline alkaloid are now underway and also will be discussed.