47 海洋天然物Fuscol及びUpialの全合成(口頭発表の部)

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Bicyclo[2.2.2]octane derivatives are versatile synthetic intermediates in total synthesis of natural products with various types of carbon skeleton. However, use of optically active bicyclo[2.2.2]octane derivatives as the synthetic precursor of total synthesis was so far limited because of the lack of effective and practical synthetic methods for them. Here, we wish to report the synthesis of optically active bicyclo[2.2.2]octane derivatives, and the total syntheses of marine terpenoids, fuscol and upial, using these bicyclo[2.2.2]octane derivatives. Sequential Michael reaction of (S,Z)-4,5-di-O-isopropylidenepent-2-enoates, (Z)-2, with the lithium enolate of cyclohexenone derivatives 1a-d gave 3a-d, respectively, with a high stereoselectivitiy (Scheme 1). On the other hand, reaction of (E)-2 with the enolate of 8 gave 12 selectively (Scheme 2). From 3d, fuscol (13) with an unique lobane skeleton, isolated from the gorgonian Eunicea fusca, was synthesized in an optically active form. The synthesis involves transformation of 3d to olefin 17, oxidative cleavage of the double bond in 17 to give 18, removal of the 1,3-dioxolane moiety of 20, and elongation of the side chain as key steps (Scheme 3). The present result defined the complete structure of fuscol to be 15. Upial (27) having a bicyclo[3.3.1]nonane system, isolated from the sponge Dysidea fragilis, was also synthesized from bicyclo[2.2.2]octane derivative 12. The synthesis involves intramolecular cyclization of 28 to give 29, acid-induced fragmentation reaction of tricyclic compound 30 to give 31, allylic oxidation of olefin 32 by use of SeO_2 in formic acid, and samarium(II) iodide-induced cyclization of diformate 42 to give 43 as key steps (Scheme 4 and Scheme 5).
天然有機化合物討論会の論文
1992-09-10

47 海洋天然物Fuscol及びUpialの全合成(口頭発表の部)

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