Searching for radical intermediates and pathways implied in the biosynthesis of some polycyclic cembranoids. A new plausible mechanism for the origin of sinulanocembranolide A in the coral Sinularia gyrosa

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• 作者：Matthew J. Palframan ; Gerald Pattenden
• 关键词：Norcembranoids ; Radical ; Biosynthesis speculation ; Sinulanocembranolide A ; Samarium diiodide ; Sinularia sp.
• 刊名：Tetrahedron Letters
• 出版年：11 December, 2013
• 年：2013
• 卷：54
• 期：50
• 页码：6822-6825
• 全文大小：844 K

文摘

The 3(2H)-furanone 11 underwent dimerisation to 13 (71%) via the captodative radical intermediate 12 on treatment with t-butyl hydroperoxide, but similar treatment of 5-episinuleptolide (5) failed to produce the natural product 7 via the presumed radical intermediate 8. In other attempts to generate 8, irradiation of a solution of 5 in benzene led only to the corresponding E-isomer 14, and treatment of 5 with Mn(OAc)₃ in HOAc produced the acetate of the isomeric alcohol 15. However, when a solution of 5-episinuleptolide (5) in THF was reacted with samarium diiodide, a sequence of transannular ketyl radical-induced coupling reactions ensued leading to the ring fused compound 20 in 62% yield. From these experiments in vitro it is difficult to make the case for the involvement of carbon-centred radical intermediates suggested earlier, in the biosynthesis of some polycyclic norcembranoids. It is proposed that the ring system in the recently described sinulanocembranolide A (1) is derived in vivo by way of a novel (3 + 2) type (possibly 1,3-dipolar) transannular cyclisation from the enedione intermediate 23 produced from 5-episinuleptolide (5).