Asymmetric syntheses of the homalium alkaloids (-)-(S,S)-homaline and (-)-(R,R)-hopromine

J Org Chem. 2012 Aug 17;77(16):7028-45. doi: 10.1021/jo3012732. Epub 2012 Aug 7.

Abstract

The highly diastereoselective conjugate additions of the novel lithium amide reagents lithium (R)-N-(3-chloropropyl)-N-(α-methylbenzyl)amide and lithium (R)-N-(3-chloropropyl)-N-(α-methyl-p-methoxybenzyl)amide to α,β-unsaturated esters were used as the key steps in syntheses of the homalium alkaloids (-)-(S,S)-homaline and (-)-(R,R)-hopromine. The asymmetric synthesis of (-)-(S,S)-homaline was achieved in 8 steps and 18% overall yield, and the asymmetric synthesis of (-)-(R,R)-hopromine was achieved in 9 steps and 23% overall yield, from commercially available starting materials in each case. These syntheses therefore represent by far the most efficient total asymmetric syntheses of these alkaloids reported to date. A sample of the (4'R,4''S)-epimer of hopromine was also produced using this approach, which provided the first unambiguous confirmation of its absolute configuration and therefore that of natural (-)-(R,R)-hopromine.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alkaloids / chemical synthesis*
  • Amides / chemistry*
  • Esters
  • Lithium / chemistry*
  • Magnetic Resonance Spectroscopy
  • Molecular Structure
  • Stereoisomerism

Substances

  • Alkaloids
  • Amides
  • Esters
  • homaline
  • hopromine
  • Lithium