Ph.D. Thesis_AS_Publishing version for IRC_12 ... - Jacobs University

Chapter 1
1.4.2.5 Cinchona based bifunctional catalysts
Cinchona alkaloid derivatives are another important class of organocatalysts used for asymmetric
reactions from the early stage of organocatalysis. 3,31 Though this is a natural class of
organocatalysts, they are less common for catalyzing the asymmetric Michael addition.
Connon and co-workers 32 used a cinchona based primary-tertiary diamine catalyst (Figure 1.6,
44) for asymmetric Michael additions. They applied their catalyst for the addition of ketones
(cyclic and acyclic) and aldehydes (unbranched and α-substituted) to nitroolefins. In comparison
with the reported literature they had superior results i.e. 10 mol% of catalyst 44 achieved upto 98
% yield, 99 % ee and 99/1 dr. These results show that not only secondary amines, but also
primary amines have the ability to convert a carbonyl to an enamine.
H 2 N
N
OMe
H
N
MeO
N
44 45
N
NH 2
Figure 1.6. Reported examples of cinchona based bifunctional catalsyts.
1.4.2.6 Miscellaneous bifunctional catalysts
Applying the same principle of a bifunctional organocatalyst, some research groups have
designed new organocatalysts which are different from the pre-existing templates (proline,
thiourea, cinchona, etc.) as shown in figure 1.7. All of these catalysts hold the two important parts
of a bifunctional catalyst in common: primary or secondary amines for the formation of a chiral
enamine and another part which attracts the electrophile and bring it into close proximity.
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