Efficient synthesis of (-)-gamma-lycorane alkaloid by two Bu3SnH-mediated radical cyclisations

Nat Prod Res. 2008;22(13):1176-88. doi: 10.1080/14786410701838205.

Abstract

An asymmetric induction using (S)-1-arylethylamine-based chiral auxiliary and two Bu(3)SnH-mediated radical cyclisations have been developed for a total synthesis of (-)-gamma-lycorane (1). The first cyclisation proceeded in 5-endo-trig manner with moderate diastereoselectivtiy to give (3aR,7aR)-octahydroindol-2-one 6b as the major product using alpha-iodo-N-(6-oxocyclohexen-1-yl)-N-[(S)-1-phenylethyl] acetamide (5b). In the second cyclisation, the radical precursor 8 was used as substrate to construct the optically active lycorane skeleton 15 which was reduced using LiAlH4 into (-)-gamma-lycorane (1).

MeSH terms

  • Alkaloids / chemical synthesis*
  • Alkaloids / chemistry*
  • Amaryllidaceae Alkaloids / chemistry*
  • Cyclization
  • Magnetic Resonance Spectroscopy
  • Molecular Structure

Substances

  • Alkaloids
  • Amaryllidaceae Alkaloids
  • lycorane