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O
O
O
(
a
R)-101
O
O
Cl
O
O
O
R
1
Ph
O
R
1
O
O
COOMe
MeOH
Et
3
N
R
1
R
2
NH
DIPEA
TBAI
CH
2
Cl
2
12 h
N
R
2
N
R
2
O
O
Ph
Ph
O
103
102
O
O
R
1
R
2
NH =
O
Bn
NH
2
86%, 96:4 dr
(
a
S)-101
O
Cl
Ph
O
O
75%, 95:5 dr
62%, 97:3 dr
Ph
O
Ph
NH
2
NH
2
48%, 95:5 dr
MeO
NH
2
97%, 97:3 dr
NH
2
H
Ph 61%, 94:6 dr
Ph
Ph
H
82%, 96:4 dr
96%, 97:3 dr
NH
73%, 93:7 dr
NH
Scheme 1.32
Dynamic kinetic resolution of
α
-chloro ester
101
in nucleophilic substitution.
Park also employed d-allofuranose as auxiliary for the dynamic kinetic resolu-
tion of
-chloro esters in nucleophilic substitutions [46]. Using the same reaction
conditions previously for d-glucose derivative
101
and benzylamine as the nucle-
ophile, dynamic resolution of
α
-chloro acetate
104
took place with high stereose-
lectivity, affording
105
in moderate isolated yield with 90 : 10 dr (
α
α
S
:
α
R
) (Scheme
1.33).
O
O
O
O
O
BnNH
2
DIEA
TBAI
CH
2
Cl
2
12 h
O
O
O
X
BnHN
O
O
O
O
R
O
R
O
104
R = Me, X = Br
R = Ph, X = Cl
105
R = Me, 81% 71:29 dr (
α
S:
α
R)
R = Ph, 69% 90:10 dr (
α
S:
α
R)
Scheme 1.33
Dynamic kinetic resolution of
α
-chloro ester
104
in nucleophilic substitution.
Based on the results, a plausible mechanism for the nucleophilic substitutions
of d-glucose derivatives and d-allose derivatives has been suggested (Figure 1.6)
[46]. The authors proposed two transition states in which the
-R group and the
C=O bond in the ester substituent adopt an
s-cis
conformation, while the ester
carbonyl group is in an eclipsed position relative to the hydrogen atom at C3 of
the furanose. The nucleophilic attack of an amine nucleophile may then be aided
by hydrogen bond formation with one oxygen atom from the 5,6-
O
and 1,2-
O
α
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