31 Barbatane型セスキテルペンの合成

概要

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Synthesis of α- and β-barbatenes (1 and 2) and gymnomitrol 3, novel tricyclic sesquiterpenes isolated from the liverworts, was achieved utilizing cycloaddition reaction of a dihydrobenzene and a cyclopentene derivative and skeletal rearrangement of the resulted bicyclo[2.2.2]octane derivative to the bicyclo[3.2.1]octane ring system. The Diels-Alder adduct 9 obtained by heating 7 and 8 in toluene was converted after demethylation to the sulfide 23 via dimesylate 22. Desulfurization of 23 yielded the common intermediate 26 for both barbatenes and gymnomitrol. Reaction of 26 with HI followed by SiO_2 chromatography afforded the rearranged ketone 35. Methylation and subsequent dehydration gave α- and β-barbatenes. For the synthesis of gymnomitrol, on the other hand, the olefine 26 was oxidized to the epoxide 37, which rearranged smoothly to the ketoalcohol 38 with alumina. Oxidation of 38 afforded the diketone 39, which is identical with the compound derived from natural gymnomitrol. Since the diketone 39, synthesized in completely different strategy, has been converted to gymnomitrol by Coates et al., the present study constitutes formally the second synthesis of natural alcohol.
天然有機化合物討論会の論文
1979-09-20