Chemistry Reference
In-Depth Information
O
O
t
Bu
t
Bu
O
CH
3
P
O
O
P
O
O
O
O
=
O
O
O
O
t
Bu
t
Bu
13c
Nu
CH(COOMe)
2
R
R
T (
o
C)
R
Nu-H
% Conv (min)
% ee
16% Conv (90 min)
96% (
S
) at -20
o
C
Ph
Ph
Me
CH
2
(COOMe)
2
BnNH
2
CH
2
(COOMe)
2
5
25
-20
100 (7)
100 (45)
12 (60)
99 (
S
)
99 (
R
)
85 (
R
)
CH(COOMe)
2
R
T (
o
C)
% Conv (min)
% regio
% ee
R
Ph
1-Naphthyl
25
25
100 (5)
100 (10)
24
34
29 (
S
)
95 (
S
)
Figure 10.6
Summary of the best results obtained using ligand
13c.
Enantioselectivities were affected by the substituent at C5 and the phosphite moie-
ties and by the configuration of C3 and C5 and the configurations of the biaryl
moieties
.
Enantioselectivities were best with ligand
13c,
which has a glucofurano-
side backbone and bulky
tert
-butyl substituents at both
ortho
and
para
positions of
the biphenyl moieties. The results also indicated that nucleophilic attack takes
place
trans
to the phosphite located on carbon atom C5 (Figure 10.7). Ligand
10c
was also used to stabilize Pd-nanoparticles. These particles catalyzed the allylic
alkylation of
rac
-1,3-diphenylprop-2-enyl acetate with dimethyl malonate, leading
to an almost total conversion of the
(R)
-enantiomer and almost no reaction with
the
(S)
-enantiomer. This gives rise to 97% ee for the alkylation product and a
kinetic resolution of the substrate recovered with ca. 90% ee [15].
Recently, furanoside ligands of
C
2
symmetry
17
and
18
- systematically modified
at positions 2 and 5 and in the biaryl phosphite ligands, and prepared from
d-glucosamine and d-glucitol (Figure 10.8) - were successfully applied in the Pd-
catalyzed allylic substitution reaction of 1,3-diphenylprop-2-enyl acetate (
S1
) using
benzylamine and dimethyl malonate under standard conditions [16]. Ligand
17
provided high activity (TOFs
>
22 000 h
−1
) and excellent enantioselectivities [up to
99% ee,
(S)
].
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