Biomedical Engineering Reference
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AuCl
3
(5 mol%)
4 steps
OTBS
OTBS
O
CH
2
Cl
2
, rt, 3 h
80%
OH
6
(dr = 60:40)
7
(dr = 60:40)
OMe
[6]
OH
HO
Citreoviridin
9
O
O
OH
O
HO
OMe
CHO
O
O
O
Verrucosidin
10
Citreoviral
8
O
O
O
SCHEME 4.6
Synthesis of citreoviral by Krause and Hoffmann-Roder.
obtained in a four-step sequence from 2-methylbut-1-en-3-yne, was efficiently
converted into dihydrofuran
in the presence of 5mol% of AuCl
3
. Notably, a
complete axial to central chirality transfer was observed for this transformation.
Dihydrofuran
7
following the route previously
described by Marshall and Pinney [6]. Krause and Hoffmann-R
7
was then converted into citreoviral
8
oder have applied
similar transformations in the enantioselective total syntheses of (
€
þ
)-linalool oxide
. A copper-mediated S
N
2
0
15
,(
)-isocyclocapitelline
21
, and (
)-isochrysotricine
22
substitution of enantioenriched epoxyalkyne
11
delivered
a
-dihydroxyallene
12
,
which was subsequently cycloisomerized to dihydrofuran
13
by treatment with
0.1mol% of AuCl
3
(Scheme 4.7). (
was finally obtained in
high stereochemical purity after a seven-step sequence consisting of the formation of
the tertiary alcohol, the reduction of the intracyclic alkene, and the conversion of the
benzyloxymethyl moiety into a vinyl group.
(
þ
)-Linalool oxide
15
21
22
, which possess a tetra-
hydrofuran ring of opposite absolute configurations to that found in (
)-Isocyclocapitelline
and (
)-isochrysotricine
þ
)-linalool oxide
15
, have also been synthesized using epoxyalkyne
16
as
the substrate
(Scheme 4.8) [7].
AuCl
3
MeMgCl
OBn
O
OBn
CuCN
(0.1 mol%)
OH
OH
OH
OH
O
(PhO)
3
P
H
THF, rt, 0.5 h
96%
OBn
11
93%
12
(dr > 99:1)
(ee = 97%)
13
(dr > 99:1)
1. DMP
2. MeMgCl
3. H
2
, Pd/C
4. IBX
55%
1. DIBAH
2. TMSCH
2
MgCl
CeCl
3
H
O
OH
(+)-Linalool oxide
15
O
O
H
3. KH
O
(dr > 99:1, ee = 97%)
77%
14
(dr > 99:1, ee = 97%)
SCHEME 4.7
Synthesis of (
þ
)-linalool by Krause and Hoffmann-Roder.
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