Organolanthanide-catalyzed hydroamination/cyclization. Efficient allene- based transformations for the syntheses of naturally occurring alkaloids

Victor M. Arredondo, Shun Tian, Frank E. McDonald, Tobin J Marks

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Abstract

The total syntheses of the pyrrolidine alkaloid (+)-197B (1) and pyrrolizidine alkaloid (+)-xenovenine (2) are described. The strategy involves enantioselective syntheses of the aminoallene, (5S,8S)-5-amino- trideca-8,9-diene (3), and the aminoallene-alkene, (5S)-5-amino-pentadeca- 1,8,9-triene (4), which then undergo regio- and stereoselective cyclohydroamination catalyzed by the organolanthanide precatalysts Cp'2LnCH(TMS)2 and Me2SiCp''((t)BuN)LnN(TMS)2 (Cp' = η5-Me5C5; Cp'' = η5-Me4C5; Ln = lanthanide; TMS = Me3Si). These reactive organolanthanide complexes efficiently mediate highly diastereoselective intramolecular hydroamination/cyclization (IHC) reactions under mild conditions. The turnover-limiting step in these catalytic cycles is proposed to be intramolecular insertion into the Ln-N bond of the proximal allenic C=C linkage, followed by rapid protonolytic cleavage of the resulting Ln-C bond. The rate and selectivity of the insertion process is highly sensitive to the steric demands of the substrate.

Original languageEnglish
Pages (from-to)3633-3639
Number of pages7
JournalJournal of the American Chemical Society
Volume121
Issue number15
DOIs
Publication statusPublished - Apr 21 1999

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ASJC Scopus subject areas

  • Chemistry(all)

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