Dirhodium(II)/Phosphine Catalyst with Chiral Environment at Bridging Site and Its Application in Enantioselective Atropisomer Synthesis

A dirhodium­(II)/phosphine catalyst with a chiral environment
at
the bridging site was developed for the asymmetric arylation of phenanthrene-9,10-diones
with arylboronic acids. In contrast to the classic chiral bridging
carboxylic acid (or derivatives) ligand strategy of bimetallic dirhodium­(II)
catalysis, in this reaction, tuning both axial and bridging ligands
realized the first Rh2(OAc)4/phosphine-catalyzed
highly enantioselective carbonyl addition reaction. The kinetic analysis
reveals that dirhodium­(II) and arylboronic acid follow the first-order
kinetics, while phenanthrene-9,10-dione is zeroth-order. These data
supported the proposed catalytic cycle, where the key intermediate
in the rate-determining step involved the dirhodium­(II) complex and
arylboronic acid. Finally, axially chiral biaryls were prepared based
on a newly developed oxidative ring-opening reaction of α-hydroxyl
ketones with a base and molecular oxygen, which featured a central-to-axial
chirality transfer radical β-scission step.