Recent Advances in the Catalytic Dearomative Double Hydrofunctionalization of Pyridines and Quinolines

Pyridines and quinolines are foundational motifs for synthesizing bioactive N-heterocycles. While dearomative single hydrofunctionalization (FG = Si, B) of N-heteroarenes to yield dihydropyridines/quinolines (DHP/DHQ) is well-established, achieving regioselective double hydrofunctionalization—specifically controlling the second C(sp 3 )–FG bond-forming step—remains a significant challenge. This Review highlights recent advancements in Lewis acidic organoborane and transition-metal catalysis for the direct synthesis of functionalized THP and THQ scaffolds. We provide a comprehensive analysis of substrate scopes, reaction mechanisms, and the origins of selectivity, contrasting the intrinsic electronic control of boron systems with the ligand-controlled pathways of Rh and Co catalysts. Finally, we offer a perspective on expanding these cascade protocols to broader conjugated systems, such as α,β-unsaturated carbonyls and dienes, through highly modular catalyst design.