Concise enantioselective total syntheses of (+)-homochelidonine, (+)-chelamidine, (+)-chelidonine, (+)-chelamine and (+)-norchelidonine by a Pd II-catalyzed ring-opening strategy

Chemistry. 2008;14(7):2112-24. doi: 10.1002/chem.200701775.

Abstract

New enantioselective syntheses of the B/C hexahydrobenzo[c]phenanthridine alkaloids (+)-homochelidonine, (+)-chelamidine, (+)-chelidonine, (+)-chelamine, and (+)-norchelidonine are described. Our rapid and convergent route to this class of natural products involved the development and application of a Pd II-catalyzed asymmetric ring-opening reaction of a meso-azabicyclic alkene with an aryl boronic acid as the key step. By screening a variety of functionalized ortho-substituted aryl boronic acids, chiral ligands and reaction conditions we were able to prepare the requisite cis-1-amino-2-aryldihydronaphthalenes in high yield and in up to 90 % ee. Early attempts to complete the synthesis of (+)-homochelidonine using an N-Boc azabicyclic alkene are described in full. The successful route required a protecting group alteration followed by B ring formation and then stereoselective installation of the C-11 syn-hydroxy group by regioselective epoxide ring-opening using a hydride source. Ring-opening of the same epoxide intermediate with water ultimately led to the synthesis of (+)-chelamidine. The same strategy was then used to synthesize the other structurally similar B/C hexahydrobenzo[c]phenanthridine alkaloids, (+)-chelidonine, (+)-chelamidine, and (+)-norchelidonine.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Benzophenanthridines / chemical synthesis*
  • Benzophenanthridines / chemistry
  • Berberine Alkaloids / chemical synthesis*
  • Berberine Alkaloids / chemistry
  • Boronic Acids / chemistry
  • Catalysis
  • Molecular Conformation
  • Organometallic Compounds / chemistry*
  • Palladium / chemistry*
  • Stereoisomerism

Substances

  • Benzophenanthridines
  • Berberine Alkaloids
  • Boronic Acids
  • Organometallic Compounds
  • chelamine
  • Palladium
  • chelidonine
  • homochelidonine