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HO
O
H
O
HO
BnO
Pb(OAc)
4
,
benzene
O
PhMgBr, THF, 0 °C
Me
O
BnO
O
O
(77%)
(92%)
Me
Me
O
14
3-
O
-Benzyl-1,2-
O
-isopropylidene-
-
D
-glucofuranose
Me
R
trans
-CH
3
CH=CHCOCl,
NaH, THF, 0 °C
O
O
HO
Me
O
O
(90%)
O
Me
O
O
Me
O
Me
18
Me
15
:R=OH
Ph
3
P, CCl
4
, reflux (75%)
16
:R=Cl
H
2
, Pd/C, AcOH/MeOH,
60psi (81%)
Me
17
:R=H
O
O
R
1
2
CuMgBr
O
O
Me
O
R
1
MgBr, CuBr•Me
2
S,
Me
2
S-THF, -78 °C
Me
s-trans
18
O
18
Me
O
R
1
yield
de
O
O
Me
O
R
1
Ph
vinyl
allyl
heptyl
Et
i
-Pr
74%
68%
69%
70%
65%
72%
95%
>90%
87%
>90%
>90%
>90%
19
Me
Scheme 2.4
Synthesis of d-xylose-derived 3-
O
-crotonyl ester
18
and subsequent 1,4-additions
with various organocuprates.
chiral auxiliaries for various carbon-carbon bond-forming reactions [6]. The
Tadano group explored extensively the difference in the spatial environment con-
stituted by each hexopyranoside configuration, which affected the diastereoselec-
tivity of the attempted organic reactions. Consequently, they synthesized various
carbohydrate-based templates from d-glucose, d-mannose, or d-galactose, in
which an unprotected hydroxyl group at C2, -3, -4, or -6 was used to introduce the
reaction site. These substrates were subjected to 1,4-addition reactions, alkylations,
cycloadditions, and other reactions. In each reaction, the Tadano group expected
that stereodifferentiation would proceed principally by the shielding effect of the
protecting group neighboring the reaction site. The sugar template was then
removed from each product by basic, acidic, or reductive treatment. As a result,
various
-chiral carboxylic acids or alcohols could be obtained in enan-
tiomerically pure or highly enriched form. In addition, the used sugar templates
could be recovered.
α
- and/or
β
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