viii
Preface
provides an important overview of the principles behind this approach to cooperative
asymmetric catalysis, and examples of its implementation in synthesis. Visible light
photocatalysis has also seen recent use with chiral organocatalysts, where in this
case electron or energy transfer offers an exciting avenue to activate new classes of
reagents towards asymmetric coupling. Xiao shows how such photocatalysts can be
merged with enamine or iminium catalysis, nucleophilic organocatalysts, or chiral
Bronsted acids to offer new avenues to create chiral products. Ohmiya describes
how another class of organocatalyst, nucleophilic N-heterocyclic carbenes, can be
used with metal catalysts. These systems exploit the two distinct catalyst systems to
simultaneously generate the nucleophilic and electrophilic components of reactions,
and do so with high levels of enantioselectivity. The broad potential of tertiary
amine catalysis when employed in concert with Lewis acids or transition metals is
reviewed by Snaddon. Chirality here can be introduced on either the tertiary amine
or metal catalyst, and has seen particular use in trapping ammonium enolates with
metal activated electrophiles. Ion pairing influences offer another attractive avenue
to develop asymmetric metal catalyzed reactions, where in this case reactivity and
selectivity can be modulated by the synergistic influence of an organic counterion
and the metal center. Ooi describes an important approach to these reactions
employing chiral cations, such as phase transfer catalysts, in concert with transition
metal catalysts. These can even be incorporated into hybrid metal catalysts that
exploit cationic bonding sites.
Liu describes how a chiral phosphoric acid, can open as well a highly tunable
system for asymmetric catalysis in concert with the first-row transition metals. The
chiral phosphoric acid here can serve many roles, including as a Bronsted acid, ion
pair with cationic metals, or coordinate as a ligand, as a tunable route to create
asymmetric reactions. Finally, Gong describes how chiral phosphoric acids in
concert with transition metal catalysts can be employed not just in single catalytic
operations, but also in relay catalysis, where the action of one of the two catalyst
systems on a reagent generates an intermediate that can be subsequently converted
to product by another catalyst. This chemistry taps into the broad array of reactivity
opened by transition metals in concert with organocatalysts, and can prove
particularly powerful in efficiently building-up complex chiral products that would
not be accessible using a single catalyst system.
We hope that this collection will prove useful for readers as an overview of the
many avenues in which the field cooperative catalysis can prove useful in the
generation of chiral products, and will serve as a useful roadmap for future
development in this burgeoning area. We would like to thank many prominent
scientists for their contribution to this work. Moreover, thanks are due to the staff at
Topics in Current Chemistry, and the editorial board for selecting us to put together
this edition.
can offer a useful approach to enamine/iminium organocatalysis. The contribution
Preface
provides an important overview of the principles behind this approach to cooperative
asymmetric catalysis, and examples of its implementation in synthesis. Visible light
photocatalysis has also seen recent use with chiral organocatalysts, where in this
case electron or energy transfer offers an exciting avenue to activate new classes of
reagents towards asymmetric coupling. Xiao shows how such photocatalysts can be
merged with enamine or iminium catalysis, nucleophilic organocatalysts, or chiral
Bronsted acids to offer new avenues to create chiral products. Ohmiya describes
how another class of organocatalyst, nucleophilic N-heterocyclic carbenes, can be
used with metal catalysts. These systems exploit the two distinct catalyst systems to
simultaneously generate the nucleophilic and electrophilic components of reactions,
and do so with high levels of enantioselectivity. The broad potential of tertiary
amine catalysis when employed in concert with Lewis acids or transition metals is
reviewed by Snaddon. Chirality here can be introduced on either the tertiary amine
or metal catalyst, and has seen particular use in trapping ammonium enolates with
metal activated electrophiles. Ion pairing influences offer another attractive avenue
to develop asymmetric metal catalyzed reactions, where in this case reactivity and
selectivity can be modulated by the synergistic influence of an organic counterion
and the metal center. Ooi describes an important approach to these reactions
employing chiral cations, such as phase transfer catalysts, in concert with transition
metal catalysts. These can even be incorporated into hybrid metal catalysts that
exploit cationic bonding sites.
Liu describes how a chiral phosphoric acid, can open as well a highly tunable
system for asymmetric catalysis in concert with the first-row transition metals. The
chiral phosphoric acid here can serve many roles, including as a Bronsted acid, ion
pair with cationic metals, or coordinate as a ligand, as a tunable route to create
asymmetric reactions. Finally, Gong describes how chiral phosphoric acids in
concert with transition metal catalysts can be employed not just in single catalytic
operations, but also in relay catalysis, where the action of one of the two catalyst
systems on a reagent generates an intermediate that can be subsequently converted
to product by another catalyst. This chemistry taps into the broad array of reactivity
opened by transition metals in concert with organocatalysts, and can prove
particularly powerful in efficiently building-up complex chiral products that would
not be accessible using a single catalyst system.
We hope that this collection will prove useful for readers as an overview of the
many avenues in which the field cooperative catalysis can prove useful in the
generation of chiral products, and will serve as a useful roadmap for future
development in this burgeoning area. We would like to thank many prominent
scientists for their contribution to this work. Moreover, thanks are due to the staff at
Topics in Current Chemistry, and the editorial board for selecting us to put together
this edition.
can offer a useful approach to enamine/iminium organocatalysis. The contribution