Biomedical Engineering Reference
In-Depth Information
56
(1 mol%)
2 M KCN aq (1.5 equiv
)
SO
2
Mes
SO
2
Mes
N
HN
Toluene, 0°C
2-8 h
R
H
R
CN
R =
c
-Hex: 89% (ee = 95%)
c
-Oct: 88% (ee = 97%)
(CH
3
)
2
CH: 85% (ee = 93%)
PhCH
2
CH
2
: 81% (ee = 90%)
t
-Bu: 94% (ee = 94%)
Ar
Ar
Me
Me
-
I
N
Ar
Ar
56
(Ar = 4-CF
3
-C
6
H
4
)
SCHEME 7.25
7.7. CYCLIZATION
Smith and coworkers developed a catalytic asymmetric 6
-electrocyclization under
phase-transfer conditions. Treatment of an
in situ
-generated
N
-aryl imine
58
with
K
2
CO
3
under the influence of
4d
afforded the cyclized product
59
in good yield with
excellent enantioselectivity (Scheme 7.26) [68].
Fini and coworkers developed a highly enantioselective [3
p
2]-cycloaddtion of
in situ
-generated nitrones with alkenes under phase-transfer conditions in the
presence of
51b
(Scheme 7.27) [69].
þ
7.8. AMINATION
We developed a catalytic asymmetric amination of
-keto esters catalyzed by a
quaternary tetraalkylphosphonium bromide (
S
)-
45
(Scheme 7.28) [70]. The reaction
b
CO
2
i
-Pr
CO
2
i
-Pr
MgSO
4
Toluene
rt
CO
2
i
-Pr
+
CO
2
i
-Pr
PhCHO
F
3
C
NH
2
F
3
C
N
Ph
57
58
4d
(10 mol%)
33% K
2
CO
3
aq
Toluene
-15°C
87%
_
+
H
Cl
N
i
-PrO
2
C
CO
2
i
-Pr
OH
N
Ph
4d
H
F
3
C
59
(ee = 94%)
SCHEME 7.26
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