Biomedical Engineering Reference
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OH
H
AuCl
3
(1 mol%)
THF, rt, 0.5 h
HO
HO
O
O
O
H
H
H
H
92%
OTBS
OTBS
25
steps
O
O
H
O
H
H
OH
O
Ca
II
OH
O
Ionomycin calcium complex
26
O
O
SCHEME 4.10
Synthesis of the ionomycin calcium complex by Kocienski and coworkers.
by Kocienski and
coworkers also highlights the synthetic interest of gold catalysis for the synthesis of
tetrahydrofuran derivatives [9] as one of the tetrahydrofuran units included in the
structure of the natural product was obtained via a Au(III)-catalyzed cyclization of
a functionalized
a
-hydroxyallene
The total synthesis of the ionomycin calcium complex
26
(Scheme 4.10).
The total syntheses of bejarols
25
, which are enantiomers of two
naturally occurring sesquiterpenoid components of the essential oil, by Krause and
coworkers represent rare examples of the application of the gold-catalyzed hydro-
xyallene cyclization to the synthesis of dihydropyran derivatives (Scheme 4.11) [10].
Hence, 5 mol% of a Au(I)-complex were required to convert
31
and
32
the mixture
of
b
-hydroxyallenes
. As in the case of
a
-hydroxyallenes, the cycloisomerization took placewith a complete axis-to-center
chirality transfer.
27
and
28
into dihydropyrans
29
and
30
H
O
OH
O
O
O
27
(Ph
3
P)AuCl (5 mol%)
29
(50%)
O
AgBF
4
(5 mol%)
H
THF, rt, 2 h
O
O
OH
O
O
28
30
(30%)
O
(
27
:
28
= 3:2)
steps
OH
OH
O
O
(
R
,
R
,
R
)-Bejarol
31
(
R
,
S
,
R
)-Bejarol
32
SCHEME 4.11
Syntheses of bejarols by Krause and coworkers.
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