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selective protection
OTr
TrO
OH
H
OTr
6
6'
O
O
OH
H
1'
O
O
H
5
O
OH
5'
1
H
O
OH
OH
OH
7a
H
1
OH
OH
NaH/Im
BnBr, DMF
OR
RO
OR
O
careful
hydrolysis
O
9a
R = Tr
9
R = H
BnO
O
OBn
BnO
OBn
OBn
Scheme 2 Preparation of 2,3,3
0
,4,4
0
-penta-O-benzylsucrose (9).
OH
R
3
SiO
OX
9
O
O
BnO
O
OBn
CO
2
H
BnO
OBn
OBn
Ph
3
P
DEAD
14a.
X = MOM
14b.
X = BOM
NO
2
selective
silylation
OH
H
OCOAr
ArCOO
OH
XO
6
6'
1. R-Cl
2. base
O
O
BnO
O
O
BnO
O
OBn
O
OBn
BnO
OBn
BnO
OBn
OBn
10
OBn
11a.
X = MOM
11b.
X = BOM
OSiR
3
R
3
SiO
OX
OSiR
3
H
selective
de-silylati
o
n
OX
O
O
O
BnO
O
BnO
O
OBn
O
OBn
BnO
OBn
BnO
OBn
OBn
OBn
13a.
X = MOM
13b.
X = BOM
12a.
X = MOM
12b.
X = BOM
the primary hydroxyl groups in 2,3,3
0
,4,4
0
-penta-O-
Scheme 3 Differentiation of
benzylsucrose.
We have found that the primary hydroxyl groups in 9 can be effectively
differentiated. Reaction of triol 9 with the Mistunobu reagent (p-nitro-
benzoic acid/TPP/DEAD) protected the hydroxyl groups at the C6 and
C6
0
-positions and gave alcohol 10. The remaining 1
0
-OH group was
protected either with methoxymethyl- or benzyloxymethyl block;
basic hydrolysis of both ester groups afforded finally diols: 11a or 11b
(Scheme 3).
19,20
Silylation of 11 (a or b) with 1 equiv. of tert-butyldimethylsilyl (TBDMS)
or tert-butyldiphenylsilyl
(TBDPS) chlorides selectively protected the
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