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In-Depth Information
H
H
H
O
O
O
O
H
2
/Pd/C
iBu
2
AlH
O
O
O
-78 °C
H
H
H
O
O
O
14
1
NaBH
4
O
O
OH
0-4
°
C
>90%
99
H
2
/Pd/C
H
NaBH
4
/
BF
3
⋅ Et
2
O
71%
O
O
O
H
81%
H
O
Qinghaosu
Derivatives
O
O
BH
3
NEt
3
-Me
3
SiCl
OH
O
98
H
O
100
Scheme 5-2
dihydroqinghaosu makes the derivation of qinghaosu possible; a detailed discussion
of this takes place in Section 5.5.
Qinghaosu can be reduced even more with sodium borohydride in the presence
of boron trifluoride to deoxoqinghaosu (100).
106
100 can also be obtained by reduc-
tion of 98 with BH
3
NEt
3
and Me
3
SiCl in DME.
107
The more powerful reducing
agent lithium aluminium hydride reduces not only lactone and peroxy group, but
also acetal and ketal, to yield the exhaustively reduced product 101 and partially
reduced products (Scheme 5-3).
108,109
5.3.2
Acidic Degradation of Qinghaosu
Treatment of qinghaosu in a mixture of glacial acetic acid and concentrated sulfuric
acid (10:1) at room temperature yields a mixture of one carbon less products,
among which several ketone-lactone or a,b-unsaturated ketone can be isolated.
110
X-ray crystal analysis of the major component 103 shows that its C-7 configuration
is inverted in comparison with that of qinghaosu.
111
An intermediate 102 for the
formation of these products has been proposed (Scheme 5-4).
H
H
H
H
O
O
HO
HO
LiAlH
4
OH
OH
1
+
+
+
HO
HO
OOH
H
OH
H
H
H
O
O
HO
O
OH
OH
101
Scheme 5-3
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