Biomedical Engineering Reference
In-Depth Information
O
O
MeMgCl
CuCN
1. DMP
2. MeMgCl
86%
OH
OH
OH
OH
(PhO)
3
P
2
2
BnO
BnO
BnO
2
98%
16
17
18
(ee = 98%)
(ee = 98%)
(ee = 98%)
AuCl
3
(0.05 mol%)
THF, rt, 0.2 h
97%
1. Tryptamine
TFA
2. Pd/C
H
H
NH
1. H
2
, Pd/C
2. DMP
H
O
O
HO
O
2
H
HO
HO
N
HO
53%
O
99%
(-)-Isocyclocapitelline
21
20
19
(dr > 99:2, ee = 98%)
(ee = 98%)
1. MeI
2. NaOH
100%
N
H
O
HO
N
22
(-)-Isochrysotricine
SCHEME 4.8
Synthesis of (
)-isocyclocapitelline and (
)-isochrysotricine by Krause and
coworkers.
The sequence previously used for the synthesis of (
þ
)-linalool oxide
15
was
16
17
slightly modified by converting epoxyalkyne
to the tertiary alcohol
.Thegold-
18
catalyzed cyclization of allene
proceeded with the same efficiency in the
presence of an extremely low loading of catalyst (0.05 mol%). The sequence was
completed by converting dihydrofuran
, which was then subjected
to a Pictet-Spengler cyclization in the presence of tryptamine. (
19
to aldehyde
20
)-Isocyclocapitel-
line
was finally obtained after an aromatization step by treatment with palladium
on charcoal. A further methylation step delivered (
21
.
Similarly, Murakami and coworkers have concisely synthesized (
)-isochrysotricine
22
)-
boivinianin B
24
in a seven-step sequence (Scheme 4.9) [8]. In this case,
a
-hydroxyallene
22
was converted into dihydrofuran
23
by using 5mol% of the
phosphine gold(I) complex [(JohnPhos)Au(CH
3
CN)]SbF
6
.
OH
[(JohnPhos)Au(CH
3
CN)]SbF
6
(5 mol%)
OH
OH
[Ir(cod)(PCy
3
)(py)]PF
6
Tol
OH
Tol
O
O
H
H
H
2
, CH
2
Cl
2
, 6 h
76%
CH
2
Cl
2
, -20°C, 3 h
22
75%
23
(dr > 94:6)
(±)-Boivinianin B
24
Tol
(dr > 94:6)
SCHEME 4.9
Synthesized of (
)-boivinianin B by Murakami and coworkers.
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