Atroposelective Access to π‐Conjugated 1,2‐Azaborepines Enabled by Palladium‐Catalyzed Cyclization of N ‐Heterobiaryls with Alkynylboronates

ABSTRACT π‐Conjugated organoboron compounds that feature N→B coordination bonds exhibit attractive photophysical and electronic properties. However, the efficient catalytic asymmetric synthesis of medium‐sized BN‐heterocycles remains underdeveloped. Herein, we report a palladium‐catalyzed atroposelective cyclization of racemic N ‐heterobiaryl triflates with alkynyl boronates, yielding a variety of 1,2‐BN‐bridged seven‐membered biaryls in high yields (up to 99%) and excellent enantioselectivity (>99% ee). The reaction occurs via a palladium‐catalyzed dynamic kinetic asymmetric transformation (DyKAT) of N ‐heterobiaryl triflates to generate a palladium species, which then undergoes cis ‐carbopalladation with the alkyne moiety of alkynylboronates, followed by a 1,2‐migration to afford the chiral π‐conjugated 1,2‐azaborepines. The reaction shows broad substrate scope and excellent functional group tolerance. And the resulting boron‐containing products are amenable to further transformations, including direct oxidation and Suzuki–Miyaura cross‐couplings.