Ligand-Controlled Regioselective Dearomative Vicinal and Conjugate Hydroboration of Quinolines

A dearomative strategy to regioselectively modify arenes using a "diene" synthon within aromatic rings provides access to highly functionalized heterocycles from abundant aromatic feedstocks and represents an alternative synthetic approach besides traditional cross-coupling and C-H functionalization methodologies. In this study, we present an efficient method for selectively introducing boron onto quinolines through dearomative hydroboration using easily accessible and stable phosphine-ligated borane complexes. The vicinal 5,6- and conjugate 5,8-hydroborated products could be obtained regioselectively by modifying the phosphine ligand. Drawing inspiration from diverse organoboron transformations, these borane building blocks were diversified by a range of downstream functionalizations, providing modular pathways for the skeletal modifications of quinolines to access a variety of challenging functionalized heterocycles.