Further studies on the oxy-functionalization of cholesteryl acetate with tert-butyl hydroperoxide and tris(acetylacetonato)iron(III).
作者:MICHIYA KIMURA、TOSHIKI MUTO
DOI:10.1248/cpb.29.1862
日期:——
The time courses of the spectral change, decomposition, and consumption of Fe (acac)3, tert-butyl (τBu) hydroperoxide, and cholesteryl acetate, respectively, in the title reaction were followed and the reaction was inferred to be initiated by the active species originating from the interaction of the ferric chelate and the hydroperoxide. Radical processes seem to participate in this reaction, since it was completely inhibited by a radical scavenger (BHT), which was also effective in blocking the further transformation of the intermediary C (7)-τBu-peroxide. The τBuBr-KO2 system generating τBuOO radicals oxidized cholesteryl methylether almost exclusively to an epoxide. The τBuOOH-KO2 system generating τBuO radicals, on the other hand, abstracted the allylic C (7)-hydrogen to give the τBu-peroxide, the alcohol, and the ketone, but no epoxide. The intermediary τBu-peroxide was assumed to be produced also by the nucleophilic attack of τBuOOH on the allylic cation, to which the initially formed C (7)-radical species was further oxidized. A proposed mechanism is presented for the title reaction.
在标题反应中,分别追踪了Fe(acac)3、叔丁基过氧化氢(τBuOOH)和胆固醇乙酸酯的光谱变化、分解和消耗的时间进程,并推测该反应由铁螯合物与过氧化氢相互作用产生的活性物种引发。由于反应被自由基清除剂(BHT)完全抑制,后者还能阻止中间体C(7)-τBu-过氧化物的进一步转化,因此自由基过程似乎参与了这一反应。产生τBuOO自由基的τBuBr-KO2体系几乎只将胆固醇甲基醚氧化为环氧化物。而产生τBuO自由基的τBuOOH-KO2体系则从烯丙位C(7)夺取氢,生成τBu-过氧化物、醇和酮,但没有环氧化物。中间体τBu-过氧化物被认为是由τBuOOH对烯丙正离子的亲核攻击产生的,最初的C(7)-自由基物种进一步氧化成烯丙正离子。为标题反应提出了一个可能的机理。