Chemistry Reference
In-Depth Information
Positive NLE
(asymmetric amplification)
Negative NLE
ee of catalyst
Figure 12.1.
Nonlinear relationship between the ee of catalyst and product.
Positive NLE (asymmetric amplification)
O
OH
OH
Ti(O-
i
-Pr)
4
, (
R
,
R
)-DET
t
-BuO
2
H
Negative NLE
O
S
S
Ti(O-
i
-Pr)
4
, (
R
,
R
)-DET, H
2
O
Me
Me
t
-BuO
2
H
Scheme 12.3.
In 1986, Kagan and others reported the fi rst example of NLE in organic reactions [4]
(Scheme 12.3). In Sharpless-Katsuki asymmetric epoxidation, positive NLE, namely
asymmetric amplifi cation, was observed. Under the same reaction conditions, negative
NLE was ascertained in asymmetric sulfi de oxidation. Kagan and others afterward
explained these phenomena by computer simulation using mathematical models, where
the formation of diastereomeric aggregation of chiral catalyst is very important [5].
The addition reaction of diethylzinc to benzaldehyde was accelerated by an amino
alcohol [6], and then chiral amino alcohols were proved to be effi cient chiral catalysts
for asymmetric alkylation by using dialkylzinc reagents [7]. Oguni reported the positive
NLE in alkylation of benzaldehyde using β - amino alcohol
1
with moderate ee as a chiral
base catalyst (Scheme 12.4) [8a]. Noyori and others consecutively reported it using their
original β - amino alcohol, (2
S
) - 3 -
exo
- (dimethylamino)isoborneol (DAIB)
2
(Scheme
