Biomedical Engineering Reference
In-Depth Information
PMP
O
HN
PMPN
O
(
R
,
R
)-
5e
(2 mol%)
1N HCl
OEt
OEt
Ph
2
C
N
+
t
-BuO
H
O
t
-Bu
THF
17% NaOH aq
Mesitylene, -20°C, 6 h
88%
NH
2
O
O
2a
48
(
syn
/
anti
= 82:18)
(
syn
isomer, ee = 91%)
NHBoc
CO
2
t
-Bu
N
CPh
2
(
syn
/
anti
= 95:5)
(
syn
isomer, ee = 82%)
O
NBoc
8d
(10 mol%)
Ph
2
C
N
+
Ar
O
t
-Bu
Ar
H
Cs
2
CO
3
(2 equiv)
PhF/Pentane (4:1)
-45°C, 48 h
95%
2a
49
(Ar = 4-MeO-C
6
H
4
)
Ar
-
2BF
4
Br
-
+
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 7.22
Palomo and coworkers reported that
N
-benzyl quininium chloride
51a
acted
as a promising catalyst for the asymmetric aza-Henry reaction under solid-liquid
phase-transfer conditions utilizing CsOH as a base.
-Amido sulfones
50
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 7.23). Unprotected
hydroxyl group on
N
-benzyl quininium chloride
51a
was found to be crucial to obtain
high enantioselectivities [57]. At the same time, Herrera, Bernardi and coworkers
reported the same asymmetric aza-Henry reaction catalyzed by
N
-benzylquininium
chloride
51a
separately. In their report, freshly ground potassium hydroxide was used
as the base (Scheme 7.23) [58].
a
NHBoc
NHBoc
51a
(10-12 mol%)
+
CH
3
NO
2
NO
2
CsOH
.
H
2
O (130 mol%)
or
KOH (5 equiv)
Toluene
-40 to -50°C
R
R
SO
2
p
-Tol
50
(ee = 80-98%)
(R = alkyl, aryl)
_
Cl
OMe
+
H
N
OH
N
51a
SCHEME 7.23
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