Rhodium(III)-Catalyzed Diastereoselective Ring-Opening of 7‑Azabenzonorbornadienes with Aromatic Ketoximes: Synthesis of Benzophenanthridine Derivatives

A rhodium­(III)-catalyzed redox-neutral ring-opening of
7-azabenzonorbornadienes
with aromatic ketoximes giving 2-arylated hydronaphthylamines in a
highly diastereoselective manner is described. Later, the 2-arylated
hydronaphthylamines were converted into highly sensitive 13,14-dehydro
benzophenanthridine derivatives by HCl hydrolysis. Further, 13,14-dehydro
benzophenanthridines were aromatized into biologically important benzophenanthridine
derivatives in the presence of DDQ. A possible reaction mechanism
was proposed and supported by deuterium labeling studies and isolation
of a rhodacycle intermediate.