- Total Syntheses of Yohimbe Alkaloids, with Stereoselection for the Normal, Allo, and 3-Epiallo Series, Based on Annelations of 4-Methoxy-1,2-dihydropyridones
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N--2,3-dihydro-4-pyridone (31) was generated in two steps (77percent yield) from tryptamine and N-methyl-4-piperidone methiodide.Its cyclization (90percent yield) and oxidation (91percent yield) provided the tetracyclic analogue 32.O-Methylation and Robinson-type annelation of these vinylogous lactams (the latter in form of its Na-carbamate) furnished the dienones 38 (64percent) and 43 (90percent).Further elaboration by cyclization and/or reduction reactions selectively provided the 15,16-didehydroyohimbinones 7 and 44.Their reductions then led to yohimbinone (52, 20percent overall yield from tryptamine), alloyohimbinone (11, 19percent overall yield), and 3-epi-alloyohimbinone (10, 23percent overall yield), which led to yohimbine (3), β-yohimbine (9), 3-epi-alloyohimbine (53), and 3-epi-17-epi-alloyohimbine (54).
- Kuehne, Martin E.,Muth, Randy S.
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p. 2701 - 2712
(2007/10/02)
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