- Synthesis of tylocrebrine and related phenanthroindolizidines by VOF 3-mediated oxidative aryl-alkene coupling
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A highly convergent strategy to prepare phenanthroindolizidines is reported involving three consecutive C-C coupling reactions. This sequence features a novel VOF3-mediated aryl-alkene coupling in the final step, which enables regioselective preparation of C5-substituted phenanthroindolizidines for the first time. This strategy has been applied to the synthesis of eight natural and unnatural members in this class to investigate the scope of this chemistry and to explore structure-activity relationships.
- Niphakis, Micah J.,Georg, Gunda I.
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supporting information; experimental part
p. 196 - 199
(2011/03/19)
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- Homoproline homologation by enolate Claisen rearrangement or direct allylation: Syntheses of (-)-trachelanthamidine, (-)-isoretronecanol and (±)-turneforcidine
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The pyrrolizidine precursors 13 and 14 are obtained both by enolate Clalsen rearrangement of the homoproline allyl ester 12 and by direct allylation of N-protected homoproline ethyl ester 15. In both cases, the reactions show poor levels of stereoselectivity. Reduction gives the corresponding alcohols 20a and 21 a which are separated and subsequently elaborated to (-)-trachelanthamidine 24 and (-)-isoretronecanol 25 respectively via reductive alkene cleavage, mesylation and spontaneous cyclisation following N-deprotection. The chiral integrity of the original proline-derived asymmetric centre is preserved throughout. A similar enolate allylation gives, with high stereoselectivity, the homologue 34 of the Geissman-Waiss lactone 32, which is similarly transformed into (±)-turneforcidine 31.
- Knight, David W.,Share, Andrew C.,Gallagher, Peter T.
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p. 2089 - 2097
(2007/10/03)
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- Oxidative Generation of N-Acyliminium Ions from N-1-(Tributylstannyl)alkyl Carboxamides and Carbamates and Their Reactions with Carbon Nucleophiles
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Oxidation of N-1-(tributylstannyl)alkyl carboxamides and carbamates with ammonium hexanitratocerate (IV) or ferrocenium hexafluorophosphate generates their N-acyliminium ions by the elimination of tributylstannyl radical under mild reaction conditions.The
- Narasaka, Koichi,Kohno, Yasushi
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p. 3456 - 3463
(2007/10/02)
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