Biomedical Engineering Reference
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OTBDPS
TBDPSO
TMSO
OTBS
TMSO
HO
AcO
AcO
OTBS
OH
(Ph
3
P)AuCl (10 mol%)
AgBF
4
(10 mol%)
THF, rt, 12 h
O
17
H
OH
H
H
H
AcO
AcO
88%
51
52
H
H
steps
HO
O
HO
HO
17
O
H
H
OH
N
H
H
N
eastern half
H
H
H
O
O
(+)-Cephalostatin 1
53
O
OH
SCHEME 4.18
Synthesis of the eastern half of (
รพ
)-cephalostatin 1 by Shair and coworkers.
When a second nucleophilic species is present in the reaction medium, it can
be added onto the vinyl ether after its reactivation by the electrophilic gold species.
This sequence finally results in the formation of a ketal such as
. Obviously, when
the two oxygen nucleophiles are part of the same molecule bearing the alkyne
functionality, bicyclic ketals of types
55
[17] can
then be produced. Given the fact that the spiroketal motif can be found in the structure
of a large variety of biologically active compounds, several studies have been carried
56
and
57
[16] or spiroketals
58
and
59
R
1
R
2
R
1
OH
HO
R
1
- O O - R
2
Au(I) or Au(III)
Au(I) or Au(III)
O
etherification
ketalization
[Au]
[Au]
54
55
Intramolecular ketalization:
R
1
OH
O
R
OH
[16b]
[16a]
O
O
R
2
R
1
R
n
R
2
HO
OH
O
n
56
57
OH
[17]
O
R
O
O
O
and
n
n
m
n
m
m
X
HO
58
59
SCHEME 4.19
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