Conspectus
The development of highly effective chiral ligands
is a key topic
in enhancing the catalytic activity and selectivity in metal-catalyzed
asymmetric synthesis. Traditionally, the difficulty of ligand synthesis,
insufficient accuracy in controlling the stereoselectivity, and poor
universality of the systems often become obstacles in this field.
Using the concept of nonequivalent coordination to the metal, our
group has designed and synthesized a series of new chiral catalysts
to access various carbon/silicon and/or multiple stereogenic centers
containing products with excellent chemo-, diastereo-, and enantioselectivity.
In this Account, we summarize a series of new phosphine ligands
with multiple stereogenic centers that have been developed in our
laboratory. These ligands exhibited good to excellent performance
in the transition-metal-catalyzed enantioselective construction of
quaternary carbon/silicon and multiple stereogenic centers. In the
first section, notable examples of the design and synthesis of new
chiral ligands by non-covalent interaction-based multisite activation
are described. The integrations of axial chirality, atom-centered
chirality, and chiral anions and multifunctional groups into a single
scaffold are individually highlighted, as represented by Ar-BINMOLs
and their derivative ligands, HZNU-Phos, Fei-Phos, and Xing-Phos.
In the second, third, and fourth sections, the enantioselective construction
of quaternary carbon stereocenters, multiple stereogenic centers,
and silicon stereogenic centers using our newly developed chiral ligands
is summarized. These sections refer to detailed reaction information
in the chiral-ligand-controlled asymmetric catalysis based on the
concept of nonequivalent coordination with multisite activation. Accordingly,
a wide array of transition metal and main-group metal catalysts has
been applied to the enantioselective synthesis of chiral heterocycles,
amino acid derivatives, cyclic ketones, alkenes, and organosilicon
compounds bearing one to five stereocenters.
This Account shows
that this new model of multifunctional ligand-controlled
catalysts exhibits excellent stereocontrol and catalytic efficiency,
especially in a stereodivergent and atom-economical fashion. Furthermore,
a brief mechanistic understanding of the origin of enantioselectivity
from our newly developed chiral catalyst systems could inspire further
development of new ligands and enhancement of enantioselective synthesis
by asymmetric metal catalysis.