Biomimetic alkaloid syntheses. 15. Enantioselective syntheses with epichlorohydrin: total syntheses of (+)-, (-)- and (.+-.)-vindoline and a synthesis of (-)-vindorosine
Efficient total syntheses of (±)-vincadifformine and (−)-tabersonine
作者:Satoshi Kobayashi、Ge Peng、Tohru Fukuyama
DOI:10.1016/s0040-4039(98)02667-7
日期:1999.2
Stereocontrolled biomimetictotalsyntheses of the title compounds are described. Our syntheses feature a highly efficient preparation of the key intermediate 11 using our novel indole synthesis methodology. A novel amine protecting protocol by means of 2,4-dinitrobenzenesulfonamides has been developed to ensure the formation of the elusive secodine (3) as well as secodine-type intermediate (4) under
Chemical transformations started from tabersonine were studied. A one-pot oxidative ring-transformation with permaleic acid in methanol yielded 17,18-dehydrovincamine. Hydroboration-oxidation of the latter compound led to alkaloid 17,18-dehydrovincamone. Hydroboration-oxidation of tabersonine resulted 14 beta-hydroxyvineadifformine and 15p-hydroxyvincadifforinine. Allowing 14 beta- and 15 beta- hydroxyvincadifformines to react with permaleic acid/methanol provided 1,14-secovincamines, serving as new evidence for the mechanism of the aspidospermane-eburnane transformation. On the other hand 18 beta-hydroxyvincamine was obtained from 14 beta-hydroxyvincadifformine by reaction with 3-chloroperbenzoic acid and successive treatment with triphenylphosphine/aqueous acetic acid.
Direct bromination or hydroxylation at C-11 in vincadifformine and tabersonine derivatives in superacids