Approaches to the synthesis of (+/-)-strychnine via the cobalt-mediated [2 + 2 + 2] cycloaddition: rapid assembly of a classic framework

J Am Chem Soc. 2001 Sep 26;123(38):9324-37. doi: 10.1021/ja016333t.

Abstract

Five synthetic approaches to racemic strychnine (1), with the cobalt-mediated [2 + 2 + 2] cycloaddition of alkynes to indoles as the key step, are described. These include the generation and attempted cyclization of macrocycle 8 and the synthesis of dihydrocarbazoles 15, 22, and 26 and their elaboration to pentacyclic structures via a conjugate addition, dipolar cycloaddition, and propellane-to-spirofused skeletal rearrangement, respectively. Finally, the successful total synthesis of 1 is discussed. The development of a short, highly convergent route (14 steps in the longest linear sequence) is highlighted by the cyclization of enynoylindole 40 with acetylene and the formal intramolecular 1,8-conjugate addition of amine 49 to form pentacycle 50. Numerous attempts toward the formation of the piperidine ring of 1 from vinyl iodide 56 were made and its successful formation via palladium-, nickel-, and radical-mediated processes is described.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Chemistry, Organic / methods
  • Cobalt / chemistry*
  • Glycine Agents / chemical synthesis
  • Magnetic Resonance Spectroscopy
  • Nickel / chemistry
  • Oxidation-Reduction
  • Palladium / chemistry
  • Poisons / chemical synthesis
  • Stereoisomerism
  • Strychnine / chemical synthesis*

Substances

  • Glycine Agents
  • Poisons
  • Cobalt
  • Palladium
  • Nickel
  • Strychnine