Biomedical Engineering Reference
In-Depth Information
catalyst
50% KOH aq
O
O
Ph
2
C
N
Ph
2
C
N
+
*
PhCH
2
Br
O
t-
Bu
O
t-
Bu
Toluene or
Toluene-CHCl
3
0°C
H
Ph
2a
3a
19a
(10 mol%): 73% (ee = 95%,
S
)
19b
(1 mol%): 84% (ee = 98%,
R
)
20
(10 mol%): 86% (ee = 92%,
S
)
+
-
R
4
N
SO
3
19
Ar
+
+
H
Bu
Bu
N
+
R
4
N =
N
or
OH
N
Ar
19a
19b
(Ar = 3,4,5-F
3
-C
6
H
2
)
+
+
H
Br
-
-
+
N
O
3
S
Q
Q
+
-
Na
+
O
=
Q
SO
3
20
N
n
SCHEME 7.7
and Plaquevent succeeded in improving the enantioselectivity by attaching the
Merrifield resin on the hydroxy moiety of the cinchonidine-derived catalyst posses-
sing the 9-anthracenylmethyl group on nitrogen (
18b
) [25].
Itsuno and coworkers reported a new type of immobilization method onto a
polymer through ionic bond to sulfonate groups. Polymer-supported chiral quaternary
ammonium salts
19a
and
19b
were easily prepared by reaction of the sulfonated
polymer with the corresponding chiral ammonium salt. The polymeric catalysts could
be applied to the alkylation of
2a
and reused without loss of reactivity and selectivity
(Scheme 7.7) [26]. On the basis of these findings, Itsuno and coworkers also
developed a novel main-chain ionic chiral polymer catalyst
20
consisting of a
quaternary ammonium sulfonate repeating unit (Scheme 7.7) [27].
The recyclable fluorous chiral phase-transfer catalyst
21
was developed by our
group and its high chiral efficiency and reusability were demonstrated in the
asymmetric alkylation of
2a
. After the reaction, (
R
,
R
)-
21
could be easily recovered
by simple extraction with FC-72 (perfluorohexanes) as a fluorous solvent and used for
the next run without any loss of reactivity and selectivity (Scheme 7.8) [28].
The catalytic and chiral efficiency of
5e
was appreciated in the asymmetric
synthesis of
isoquinoline derivatives, which are important conformationally
a
0
-dibromo-
o
-xylene under
liquid-liquid phase-transfer conditions in the presence of (
S
,
S
)-
5e
showed complete
consumption of the starting Schiff base. Imine hydrolysis and subsequent treatment
constrained
-amino acids. Treatment of
2a
with
,
a
a
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