208
M. Rueping, E. Sugiono
9
Development of the First Brønsted Acid Assisted Enantioselective
Brønsted Acid Catalyzed Direct Mannich Reaction . . . . . . . . 236
10
Cooperative Co-Catalysis: The Effective Interplay
of Two Brønsted Acids in the Enantioselective Synthesis
of Isoquinuclidines . . . . . . . . . . . . . . . . . . . . . . . . . 238
11
Asymmetric Brønsted Acid Catalyzed Carbonyl Activation:
The First Organocatalytic Electrocyclic Reaction . . . . . . . . . . 241
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
Abstract. The design of catalytic reactions that proceed with high enantioselectivity is an important goal in organic synthesis. Increased interest in this
research area has resulted in substantial progress, particularly in the field of
metal catalyzed transformations. In recent years small organic molecules have
been used as organocatalysts for a variety of enantioselective reactions. Among
these, secondary amine catalysts are the most widely applied and can be used in
the activation of the nucleophilic component through enamine formation (enamine catalysis), or by formation of an iminum intermediate to activate the electrophile (iminium catalysis). Additionally, chiral diols and thioureas, as well
as carbene- and DMAP-derivatives (hydrogen bonding-, nucleophilic catalysis), have been shown to be versatile catalysts for enantioselective transformations. An alternative to these strategies is the activation of an electrophile or
nucleophile by use of a chiral Brønsted acid. Compared to amino-, carbene-,
pyridine- and hydrogen-bonding catalyzed transformations, enantioselective
Brønsted acid catalysis has only recently emerged as important and promising
area of research. In the course of our research program we were able to contribute significantly to the field of enantioselective Brønsted acid catalysis over
the last 2 years, and could demonstrate for the first time that in various enantioselective transformations chiral Brønsted acid catalysts can give better or at
least comparable results to metal-catalyzed processes. In this chapter we will
highlight some of our most recent results and will, additionally, describe how
we initially entered the field of asymmetric Brønsted acid catalysis by starting
of from a biomimetic approach using nature as a role model.
M. Rueping, E. Sugiono
9
Development of the First Brønsted Acid Assisted Enantioselective
Brønsted Acid Catalyzed Direct Mannich Reaction . . . . . . . . 236
10
Cooperative Co-Catalysis: The Effective Interplay
of Two Brønsted Acids in the Enantioselective Synthesis
of Isoquinuclidines . . . . . . . . . . . . . . . . . . . . . . . . . 238
11
Asymmetric Brønsted Acid Catalyzed Carbonyl Activation:
The First Organocatalytic Electrocyclic Reaction . . . . . . . . . . 241
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
Abstract. The design of catalytic reactions that proceed with high enantioselectivity is an important goal in organic synthesis. Increased interest in this
research area has resulted in substantial progress, particularly in the field of
metal catalyzed transformations. In recent years small organic molecules have
been used as organocatalysts for a variety of enantioselective reactions. Among
these, secondary amine catalysts are the most widely applied and can be used in
the activation of the nucleophilic component through enamine formation (enamine catalysis), or by formation of an iminum intermediate to activate the electrophile (iminium catalysis). Additionally, chiral diols and thioureas, as well
as carbene- and DMAP-derivatives (hydrogen bonding-, nucleophilic catalysis), have been shown to be versatile catalysts for enantioselective transformations. An alternative to these strategies is the activation of an electrophile or
nucleophile by use of a chiral Brønsted acid. Compared to amino-, carbene-,
pyridine- and hydrogen-bonding catalyzed transformations, enantioselective
Brønsted acid catalysis has only recently emerged as important and promising
area of research. In the course of our research program we were able to contribute significantly to the field of enantioselective Brønsted acid catalysis over
the last 2 years, and could demonstrate for the first time that in various enantioselective transformations chiral Brønsted acid catalysts can give better or at
least comparable results to metal-catalyzed processes. In this chapter we will
highlight some of our most recent results and will, additionally, describe how
we initially entered the field of asymmetric Brønsted acid catalysis by starting
of from a biomimetic approach using nature as a role model.