Intramolecular Acetyl Transfer to Olefins by Catalytic C-C Bond Activation of Unstrained Ketones.

A rhodium-catalyzed intramolecular acetyl-group transfer has been achieved through a "cut and sew" process. The challenge arises from the existence of different competitive pathways. Preliminary success has been achieved with unstrained enones that contain a biaryl linker. The use of an electron-rich N-heterocycilc carbene (NHC) ligand is effective to inhibit undesired β-hydrogen elimination. Various 9,10-dihydrophenanthrene derivatives can be prepared with excellent functional-group compatibility. The 13 C-labelling study suggests that the reaction begins with cleavage of the unstrained C-C bond, followed by migratory insertion and reductive elimination.