Chemistry Reference
In-Depth Information
Chiral
catalyst
C
∗
X
% ee
D
∗
+
A
B
Y
% ee
X
<
Y
Scheme 12.1.
General scheme of positive nonlinear effect in asymmetric synthesis.
Asymmetric
auto
catalysis
The
same
structure
The
sa
me
configuration
P
*
Asymmetric autocatalyst
A
+
B
P
*
Product
Conventional asymmetric catalysis
Di
ff
ere
nt
structures
C
*
Chiral catalyst
A
+
B
P
∗
Product
Scheme 12.2.
Asymmetric autocatalysis and conventional asymmetric synthesis.
ee has been reported, that is, the ee of the initial chiral molecule increases from very
low to very high during automultiplication.
This chapter presents an overview of asymmetric amplifi cation [1] and asymmetric
autocatalysis [2,3] .
12.2. ASYMMETRIC AMPLIFICATION
12.2.1. The History of Asymmetric Amplifi cation
When a chiral catalyst acts as a monomer throughout the reaction in a solution, the
relationship between the enantiomeric excess (ee) of the chiral catalyst (or chiral ligand)
and the obtained chiral compound should be linear. On the contrary, when a chiral cata-
lyst forms aggregate, such as a dimer and trimer, the relationship possibly deviates from
linearity by the diastereomeric recognition and interaction, and the relationship is called
NLE. There are positive and negative NLEs; however, the former is more attractive in
the synthetic point of view, where a chiral catalyst with lower ee gives a chiral product
with higher ee, and it is named as “asymmetric amplifi cation ” (Fig. 12.1 ).
