A new Ni(II)/bisimidazoline (Bim)-catalyzed asymmetric higher-order (5+3) annulation of 2-(2-aminoaryl)indoles and β,γ-unsaturated α-ketoesters is reported, enabling stereoselective access to tri- and tetracyclic indoles containing a saddle-shaped eight-membered-ring bridged biaryl architecture in moderate to good yields. When subjected to the reaction conditions, 1-(2-indolyl)naphthalen-2-amines functioning as 1,5-dinucleophilic partners underwent efficient higher-order cyclization to afford tetracyclic indoles with high diastereo- and enantioselectivity. In parallel, N-protected 2-(2-aminophenyl)indoles effectively served as alternative 1,5-dinucleophiles, delivering tricyclic indoles with comparable stereocontrol. The present protocol demonstrates good functional group tolerance, a broad substrate scope and mild reaction conditions, thereby providing a robust and alternative approach to accessing chiral medium-sized bridged biaryls.

Key words: Ni(II)/Bim catalytic system, higher-order (5+3) annulation, asymmetric catalysis, bridged biaryls, saddle-shaped eight-membered azaheterocycle