Cobalt-Catalyzed Tandem C-H Activation/C-C Cleavage/C-H Cyclization of Aromatic Amides with Alkylidenecyclopropanes.

A cobalt-catalyzed chelation-assisted tandem C-H activation/C-C cleavage/C-H cyclization of aromatic amides with alkylidenecyclopropanes is reported. This process allows the sequential formation of two C-C bonds, which is in sharp contrast to previous reports on using rhodium catalysts for the formation of C-N bonds. Here the inexpensive catalyst system exhibits good functional-group compatibility and relatively broad substrate scope. The desired products can be easily transformed into polycyclic lactones with m-CPBA. Mechanistic studies revealed that the tandem reaction proceeds through a C-H cobaltation, β-carbon elimination, and intramolecular C-H cobaltation sequence.