An ovel palladium(II)-catalyzed [5+ +2] oxidative annulation of readily available o-arylanilines with alkynes has been developed for building aseven-membered N-heterocyclic architecture containing ab iaryl linkage.T his method is applicable to aw ide range of unprotected o-arylanilines and internal alkynes,and results in the chemoselective preparation of imine-containing dibenzo [b,d]azepines in high yields with excellent diastereoselectivity with respect to the two types of stereogenic elements.Dibenzo [b,d]azepines represent an important class of medium-sized N-heterocycles because they are the key structural motifs in many natural products and bioactive compounds ( Figure 1). Forexample,dimeric erythrivarine B, which contains the seven-membered skeleton, was isolated from cultivated E. variegata.[1] LY-411575 was identified as an effective g-secretase inhibitor for the treatment of melanoma and Alzheimers disease. [2] Functionalized dibenzo [b,d]azepines were also investigated as serotonin (5-HT) receptor [3] and potassium channel inhibitor.[4] Therefore, the search for new reliable synthetic approaches for the preparation of dibenzo [b,d]azepines from readily available starting materials is of great interest.Recently,t ransition-metal-catalyzed C À Hf unctionalization has emerged as an efficient and versatile method for accessing various heterocycles and carbocycles.[5] In particular, nitrogen-group-assisted heteroannulations of nitrogencontaining coupling partners with alkynes by aC À Hcleavage/ alkyne insertion/cyclization cascade have been widely used to generate structurally diverse N-heterocyclic compounds,such as indoles, [6] pyrroles, [7] isoquinolines, [8] isoquinolinones, [9] and so on.[10] Remarkably,m ost of these transformations were realized by formal [3+ +2] or [4+ +2] cycloadditions to give fiveor six-membered rings,but the construction of larger rings by means of related annulations is quite rare. [10c,e] In this context, we set out to develop anew type of [5+ +2] annulation between simple biaryl precursors and alkynes involving aC À H activation step for the synthesis of functionalized dibenzo-[b,d]azepines. [11] This work originated from our recent studies on ruthenium(II)-catalyzed oxidative annulation of o-arylphenol derivatives with alkynes through aC À Ha ctivation strategy (Scheme 1a).[12] It is noteworthy that the reaction proceeded exclusively by ad earomatizing [3+ +2] annulation pathway to generate spirocyclic enones as the sole product, but not dibenzoxepines through apossible [5+ +2] cycloaddition route. Presumably,aclear steric clash between the two twisted aromatic groups of the intermediate A played ak ey role in driving the essential ring contraction from A to B,t hus hampering the reductive elimination of A to form adibenzoxepine and rendering the [3+ +2] spiroannulation more favorable than as even-membered ring formation. Moreover, ar ecent seminal report from the group of MascareÇas and Gulías demonstrated that simple o-vinylphenols (R = H), which cannot enga...