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OAc
O
O
S
t
Bu
OPPh
2
O
SR
O
O
O
OPPh
2
36
35
D-galacto
D-arabino
a
R =
t
Bu;
b
R = 2-OMe-C
6
H
4
;
c
R = 4-Me-C
6
H
4
Nu
Ph
Ph
L
Nu-H
% ee
35a
35a
36
36
CH
2
(COOMe)
2
BnNH
2
CH
2
(COOMe)
2
BnNH
2
96 (
S
)
96 (
R
)
84 (
R
)
88 (
S
)
Figure 10.18
Phosphinite-thioether ligands
35
and
36:
summary of the best results obtained
in the Pd-catalyzed allylic substitution of
S1.
10.2.3.2
P-N Ligands
Several types of P,N-donor carbohydrate ligands have been developed for use in
Pd-asymmetric allylic substitutions. In particular, many phosphorus-oxazoline
ligands have produced excellent results.
Kunz and coworkers developed a phosphine-oxazoline ligand
37
derived from
d-glucosamine for the Pd-catalyzed allylic alkylation of dimethyl malonate to
symmetrically and non-symmetrically substituted allyl acetates with high enanti-
oselectivities (up to 98% ee) (Figure 10.19) [28]. These results are in agreement
with a nucleophilic attack
trans
to the phosphorus atom.
Uemura and coworkers have developed a series of phosphinite-oxazoline
ligands
38
for the Pd-catalyzed allylic substitution reactions (Scheme 10.13) [29].
These ligands are prepared from the commercially available d-glucosamine hydro-
chloride. They showed high enantioselectivity with 1,3-diphenylprop-2-enyl acetate
OPiv
O
PivO
PivO
D-
gluco
O
N
37
Ph
2
P
Figure 10.19
Phosphine-oxazoline ligand
37
developed by Kunz and coworkers.
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