| Abstract
| - The highly convergent stereocontrolled total synthesis of (−)-vincamajinine (7), (−)-11-methoxy-17-epivincamajine (9), and the oxygen-bridged (+)-dehydrovoachalotine (22) are described. Key stepsin the synthesis of 7 and 9 involved the stereospecific enolate-driven palladium-catalyzed cross-coupling reaction, a Tollens reaction, an acid-assisted intramolecular cyclization to form the C(7)−C(17) quaternary center, and two stereospecific reductions. The efficiency of this strategy isillustrated by the completion of the synthesis of 7 and 9 in 16 [from d-(+)-tryptophan methyl ester17] and 17 (from the Schöllkopf chiral auxiliary 27) reaction vessels, respectively. This constitutesthe first total synthesis of these indole alkaloids and provides the first regiospecific route to 11-methoxy-substituted ajmaline/vincamajine-related alkaloids. The synthesis of 22 required a novelDDQ-mediated cyclization to furnish the C(6)−O(17) bond, executed in stereospecific fashion.Completion of these syntheses illustrates a concise and versatile strategy for the synthesis ofvincamajine-related alkaloids, which has also been employed to prepare the related compoundsquebrachidine diol (53), vincamajine diol (56), and vincarinol (59).
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