Enantio- and regioselective [2 + 2 + 2] cycloaddition of BN-diynes for construction of C-B axial chirality

Transition-metal-catalyzed asymmetric [2 + 2 + 2] cycloaddition of alkyne or nitrile motifs has received tremendous interest as it offers numerous possibilities to construct structurally diverse aromatic scaffolds with different chirality units. However, the use of these reactions is largely limited to symmetric alkynes, and the potential to use this strategy to design and construct chiral molecules is far from being explored. In this work, we report the transition-metal-catalyzed asymmetric [2 + 2 + 2] cycloaddition reactions of designed unsymmetric BN-diynes with nitriles or unsymmetric alkynes. This method offers practical access to the challenging atropisomers bearing a C-B axis with generally excellent regioselectivities and high enantioselectivities. Mechanistic studies revealed that the BN-naphthalenyl moiety of diynes is critical for the regioselectivity of this [2 + 2 + 2] cycloaddition.