Rhodium-Catalyzed Cyclocarbonylation of Ketimines via C–H Bond Activation

A novel
rhodium-catalyzed oxidative cyclocarbonylation of ketimines
via cleavage of two C–H bonds was established, which provided
a direct and reliable method for the synthesis of a wide range of
3-methyleneisoindolin-1-ones with mostly moderate yields. Preliminary
experimental mechanistic studies and DFT calculations revealed that
this reaction proceeds via imine–enamine tautomerization, N–H
cleavage, C–H bond activation, CO insertion, and reductive
elimination. The mechanism studies further ruled out an isolated cyclometalated
rhodium complex being involved in the present reaction, which was
different from many other documented rhodium-catalyzed C–H
cyclization reactions.