Biomedical Engineering Reference
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O
O
27
(1 mol%)
O
O
Br
+
CbzHN
CbzHN
K
3
PO
4
aq
CPME
-15°C, 2 h
85%
N
N
Ph
Ph
Me
Me
36
37
(de = 86%)
Ph
-
O
Cl
Ar
Ar
SiMe
2
t
-Bu
H
2
N
O
t
-Bu
H
Ph
Ph
N
N
+
O
Ph
120°C, 10 h
95%
P
Ar =
N
N
Ph
Ph
SiMe
2
t
-Bu
Ar
27
Ar
Ph
Ph
O
O
H
N
CbzHN
O
t
-Bu
N
H
N
H
Me
O
O
Ph
38
SCHEME 7.17
followed by reductive amination was effected with Hantzsch ester and CF
3
COOH in
aqueous EtOH to furnish octahydropyrrolizine core structure
44
with excellent
enantioselectivity in the one-pot reaction. The octahydropyrrolizine
44
was trans-
formed to (
)-monomorine in three additional steps (Scheme 7.18) [48].
Asymmetric conjugate addition of
þ
-cyanoacetates to acetylenic
esters under phase-transfer condition is quite challenging because of the difficulty to
control the stereochemistry of the product. We developed highly enantioselective
conjugate additions of
-substituted-
a
a
-cyanoacetates to acetylenic esters catalyzed by
(
S
)-
41b
(Scheme 7.19) [49]. In this asymmetric transformation, an all-carbon
quaternary stereocenter can be constructed in a high enantiomeric purity. This
reaction was extended to the highly enantioselective conjugate addition of
b
-keto
esters to acetylenic ketones catalyzed by (
S
)-
41c
(Scheme 7.19) [50].
a
-alkyl
a
O
Ph
2
C
N
O
OR
(
S
)-
41a
(1 mol%)
H
Ph
2
C
N
2c
(R = CH(
t
-Bu)
2
)
OR
Hantzsch ester
+
N
CsCl, K
2
CO
3
CPME
0°C, 12 h
CF
3
COOH
EtOH/H
2
O
52%
H
O
O
H
CO
2
R
Me
O
O
O
O
42
43
44
(ee = 93%)
F
F
F
Ar
-
H
Br
+
N
O
Ar =
N
H
F
H
(CH
2
)
3
CH
3
Me
(+)-Monomorine
Ar
F
(
S
)-
41a
F
SCHEME 7.18
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