Biomedical Engineering Reference
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n
-C
7
H
15
[Au]
-
HO
HO
n
-C
7
H
15
HO
n
-C
7
H
15
Au(OAc)
3
(5 mol
%
)
O
O
CF
3
COO
CHO
ClCH
2
CH
2
Cl/TFA
(10:1), rt, 1 min
-
OH
OH
OH
36
37
38
1. IBX, TBAI, rt
2. Na
2
S
2
O
3
84% (2 steps)
O
n
-C
7
H
15
O
n
-C
7
H
15
n
-C
7
H
15
COCl,
i
-Pr
2
NEt
O
O
O
HO
n
-C
7
H
15
O
DMAP, CH
2
Cl
2
, rt
61%
O
O
S-15183a
40
39
SCHEME 4.14
Synthesis of the sphingosine kinase inhibitor S-15183a by Porco and
coworkers.
Not only a hydroxyl group but also a keto functionality can serve as a
nucleophile in a gold-catalyzed 6-
endo
cyclization. Hence, aldehyde
was used
by Porco and coworkers as the substrate in the gold-catalyzed formation of the
benzopyrylium salt
36
. The latter was then used as a key intermediate in the synthesis
of the sphingosine kinase inhibitor S-15183a
38
40
and related azaphilone natural
products (Scheme 4.14) [11]. The benzopyrylium salt
38
was proposed to be formed
by protonation of the gold-ate complex
.
In 2009, Di´guez-Vazquez and coworkers reported another approach to the
synthesis of pyran rings by a gold-catalyzed double hydroalkoxylation of
d
-hydro-
xyalkynoates such as
37
(Scheme 4.15) [12]. This method could be used for the
preparation of
b
-pyranoacetal esters of type
41
42
, which are substructures of numerous
polyketide natural products such as (
þ
)-acutiphycin
43
.
, a flavonoid isolated from
Cyperus capitatus
and contributes to the pigmentation of flowers and fruits, has
been reported by Pale and coworkers. (Scheme 4.16) [13]. A selective gold(I)-
catalyzed 5-
exo
cyclization of
g
-hydroxyalkyne
A rapid and efficient total synthesis of aurone
46
, which can be easily synthesized
from 3,5-dimethoxy salicylaldehyde, was used to produce the benzofuran derivative
45
44
. A final oxidation step delivered the targeted aurone
46
.
R
2
R
2
1. AuCl
3
(2 mol%)
R
4
OH, rt, 2.5 h
2. NaHCO
3
(sat.)
R
3
O
2
C
R
3
O
2
C
HO
OH
R
1
O
OR
4
R
1
75-99%
41
42
O
H
OH
O
O
O
OPMB
Examples:
n
-Bu
OH
EtO
2
C
EtO
2
C
(+)-Acutiphycin
43
O
OMe
O
OMe
(99%)
(98%)
SCHEME 4.15
Di´guez-Vazquez's method for the synthesis of pyran rings.
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