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 CC 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, beta-carbon elimination, and intra-molecular C-H cobaltation sequence.