Rhodium-catalyzed construction of boron-based point and axial chirality via asymmetric annulation of alkynylborons

Boron-stereogenic and C–B axially chiral compounds featuring boron-based chirality represent a rarely explored class of chiral scaffolds. Reported herein is asymmetric access to boron-stereogenic and C–B axially chiral (hetero)cycles via rhodium-catalyzed C–H activation of (hetero)arenes en route to [4 + 2] or [3 + 2] annulation with two classes of boron-functionalized alkynes. The annulation of tetracoordinate gem-dialkynylboron with two classes of arenes affords B-stereogenic (hetero)cycles via desymmetrization of the diyne. The employment of tricoordinate, sterically hindered boron-functionalized alkynes in [4 + 2] annulation with 2-carboxamide-functinalized indole affords C–B axially chiral biaryls via C(3)–H activation of the indole ring (up to 99% ee). All the coupling reactions proceed with good functional group tolerance, chemoselectivity, and high enantioselectivity under mild reaction conditions, requiring no stoichiometric amount of oxidant. The chiral product exhibits limited configurational stability that is intrinsic in boron-based chirality. Moreover, the coupling system allows delivery of chiral organoboron compounds bearing diverse drug-like molecular scaffolds. Photophysical properties of representative axially chiral products have been explored.