Chemistry Reference
In-Depth Information
PMP
O
PMPN
O
H
N
(
R
,
R
)-
5e
(2 mol %)
Ph
2
CN
OEt
1 N HC
l
OEt
+
O
t
-Bu
H
t
-BuO
17% NaOH
aq
Mesitylene
-20°C, 6 h
THF
O
NH
2
O
2a
34
88% (
syn
/
anti
= 82:18)
91% ee (
syn
isomer)
NHBoc
CO
2
t
-Bu
O
8d
(10 mol %)
NBoc
Ph
2
CN
+
Ar
O
t
-Bu
Ar
H
Cs
2
CO
3
(2 equiv)
PhF/Pentane (4:1)
-45°C, 48 h
N
CPh
2
95% (
syn
/
anti
= 95:5)
82% ee (
syn
isomer)
2a
35
(Ar = 4-MeO-C
6
H
4
)
-
Ar
Br
-
+
2BF
4
4-F-C
6
H
4
Me
4-Me-C
6
H
4
+
N
O
4-Me-C
6
H
4
N
4-Me-C
6
H
4
O
+
N
Me
4-Me-C
6
H
4
4-F-C
6
H
4
Ar
(
R
,
R
)-
5e
(Ar = 3,4,5-F
3
-C
6
H
2
)
8d
Scheme 2C.18.
Palomo and others reported that
N
- benzyl quininium chloride
37
acted as a promis-
ing catalyst for the asymmetric aza-Henry reaction under solid-liquid phase-transfer
conditions utilizing cesium hydroxide as a base.
- Amido sulfones
36
were used to
generate reactive
N
- carbamoyl imines
in situ
and succeeded in aza-Henry reactions of
not only aromatic imines but also aliphatic imines (Scheme 2C.19). The unprotected
hydroxyl group on
N
- benzyl quininium chloride
37
was found to be crucial to obtain
high enantioselectivities [44]. At the same time, Herrera, Bernardi, and others reported
the same asymmetric aza-Henry reaction catalyzed by
N
- benzylquininium chloride
37
separately. In their report, freshly ground potassium hydroxide was utilized as a base
(Scheme 2C.19 ) [45] .
α
2C.6. EPOXIDATION AND AZIRIDINATION
The catalytic asymmetric epoxidation of electron-defi cient olefi ns, particularly
-
unsaturated ketones, has been the subject of numerous investigations and a number of
useful methodologies have been elaborated. Among these, the method utilizing chiral
phase-transfer catalysis occupies a unique place featuring its practical advantages, and
it allows highly enantioselective epoxidation of
trans
-
α
,
β
α
,
β
- unsaturated ketones, particu-
larly chalcone (Scheme 2C.20 ).
Chiral aziridines have been used as chiral auxiliaries, chiral ligands for transition
metals, and chiral building blocks for preparation of biologically active species such as
