A Short Total Synthesis of Benzophenanthridine Alkaloids via a Rhodium(III)-Catalyzed C-H Ring-Opening Reaction

J Org Chem. 2021 Nov 5;86(21):14826-14843. doi: 10.1021/acs.joc.1c01612. Epub 2021 Sep 28.

Abstract

The biologically important naturally available benzophenanthridines were prepared efficiently in three steps with overall good yields. A new synthetic methodology involving a rhodium(III) catalyzed redox-neutral ring-opening of 7-azabenzonorbornadienes with aromatic aldoximes is developed to synthesize the target molecules. The developed C-H ring-opening reaction is highly diastereoselective and compatible with various sensitive functional group substituted aromatic aldoximes as well as substituted 7-azabenzonorbornadienes. The ring-opening products were transformed into highly sensitive 13,14-dehydrobenzo phenanthridine derivatives by HCl hydrolysis. Subsequently, 13,14-dehydrobenzophenanthridines were converted into biologically important benzophenanthridine alkaloids in the presence of DDQ. A possible reaction mechanism was proposed for the C-H ring-opening reaction and supported by the deuterium labeling studies.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alkaloids*
  • Benzophenanthridines
  • Catalysis
  • Rhodium*

Substances

  • Alkaloids
  • Benzophenanthridines
  • Rhodium