SEARCH

SEARCH BY CITATION

Keywords:

  • Stemona alkaloids;
  • spirolactone;
  • SmI2;
  • organozinc reagent;
  • sessilifoliamide J

Abstract

Some Stemona alkaloids belonging to the tuberostemospironine group possess a spirolactone moiety with anti-configuration (C-9/C-9a). In this paper, we describe two approaches to this structural unity. By using bromine atom as a traceless directing group, the SmI2-mediated reductive coupling of ketone 6 and β-bromomethacrylate proceeded with complete anti-diastereoselectivity. In the absence of an α-directing (chelation) group, the one-pot reaction of the ketone derived from alcohol 15 with the organozinc reagent generated from bromomethacrylate afforded spiro-α-methylene-γ-lactone derivative 16 as a single diastereomer. These two highly diastereoselective methods would find application in the synthesis of stemona alkaloids containing anti-configured spiro-lactone/pyrrolidine moieties. In addition, on the basis of our previous work, the total synthesis of (−)-9-epi-11-demethylsessilifoliamide J (11), and an improved synthesis of (−)-9,11-di-epi-sessilifoliamide J (9) were accomplished.