Chemistry Reference
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Table 1 Iron salts-catalyzed transformations of persilylated
D
-glucopyranoside deriva-
tives 50 and 51.
PhCHO 3 equiv
Et
3
SiH 1.1 equiv
catalyst
OTMS
Ph
O
O
O
O
TMSO
TMSO
O
X
X
TMSO
HO
CH
2
Cl
2
/CH
3
CN: 4/1
0 °C to rt
1.5-2h
Ph
50
:X =
α
-OMe
52
:X =
α
-OMe
53
51
:X =
β
-SPh
:X =
-SPh
β
Entry
X
Catalyst
Mol%
Yield%
1
α-OMe
FeCl
3
6H
2
O
5
77
66
a
2
a-OMe
FeCl
3
6H
2
O
1
3
a-OMe
FeCl
3
5
75
-
b
4
a-OMe
Fe(acac)
3
5
-
b
5
a-OMe
(FeCl
3
)
2
(TMEDA)
3
2.5
14
a,c
6
a-OMe
Fe(NO
3
)
3
9H
2
O
5
-
a,d
7
a-OMe
FeCl
2
4H
2
O
5
8
β-SPh
FeCl
3
6H
2
O
5
71
a
Overnight reaction.
b
Starting material was recovered.
c
The 4,6-O-benzylidene derivative was obtained in 68% yield.
d
CH
2
Cl
2
was used instead of CH
2
Cl
2
/CH
3
CN; only the 4,6-O-benzylidene derivative was
isolated in 53% yield. acac
=
acetylacetone; TMEDA
=
N,N,N
0
,N
0
-tetramethylethylenediamine.
TMSO
TMSO
TMSO
O
50
: X =
α
-OMe
51
: X =
β
-SPh
X
TMSO
Ph
O
O
O
Ph
O
O
Ph
tandem
catalysis
a
then
additive(s)
OMe
Et
3
SiH
5 equiv
Ac
2
O
5 equiv
HO
O
O
O
54
, 64%
O
HO
Ph
OMe
Ph
O
O
59
, 55%
b
O
Ph
O
O
Ph
OMe
HO
O
O
O
SPh
55
O
, 58%
C
15
H
31
HO
Ph
58
, 54%
b
Ph
O
O
O
O
Ph
O
O
O
O
SPh
Ph
OMe
O
O
O
Ph
56
, 60%
O
57
, 60%
a
see
Scheme 14 Three-step transformations catalyzed by iron(
III
) chloride in one-pot.
Table 1;
b
simultaneous addition of 5 mol% more of FeCl
3
6H
2
O was required.
glycosyl acceptors (Scheme 14). Hence, terminal addition of acetic an-
hydride, palmitoyl chloride or pivaloyl anhydride afforded the orth-
ogonally protected monosaccharides 54-57 in good yields. Noteworthy, a
higher temperature was required to proceed with a sterically hindered
acylating reagent.
The combination of iron(
III
) chloride with triethylsilane can also pro-
mote the regioselective 4,6-O-benzylidene ring opening. Our results
showed that the addition of an excess of the reducing reagent was re-
quired for completion. Accordingly, persilylated pyranoside 50, treated
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