Cobalt(II)‐Catalyzed [5+2] C−H Annulation of o‐Arylanilines with Alkynes: An Expedient Route to Dibenzo‐[b,d]azepines.

The first example of CoCl2‐catalyzed formal [5+2] oxidative annulation of o‐arylanilines with alkynes was developed, giving access to various important imine‐containing dibenzo‐[b,d]azepine scaffolds through sequential C−C/C−N bond formation. The reaction employs catalytic amount of manganese and oxygen as cooxidants, and features a broad substrate scope. Preliminary mechanistic studies suggested that C−H activation is involved in the rate‐determining step. Moreover, both internal and terminal alkynes are well tolerated in this transformation. Besides, a regioselective migratory insertion was observed when using terminal alkynes as substrates. [ABSTRACT FROM AUTHOR]