Biomedical Engineering Reference
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NH
2
NaAuCI
4
·
2H
2
O (5 mol%
)
CH
3
CN, 80°C, 1 h
reduction
R
N
R
H
n
-C
11
H
23
Solenopsin A
116
114
115
R =
n
-C
11
H
23
R =
n
-C
11
H
23
(90%)
(92%)
117
118
R =
R =
SCHEME 4.34
tetrachloroaurate (NaAuCl
4
) in refluxing acetonitrile produces the 2,6-disubstituted
tetrahydropyridines
in excellent yields (Scheme 4.34) [32]. These two
compounds are components present, respectively, in the venom of the
Solenopsis.
xyloni
and
Solenopsis
ant species. Tetrahydropyridine
115
and
118
115
is itself a precursor of the
piperidine alkaloid solenopsin A
.
More recently, Fukuyama and coworkers reported that the indoline core
structure of the alkaloid (
116
)-mersicarpine
121
could be synthesized by a gold-
catalyzed
intramolecular
hydroamination
of
an
ortho
-akynylaniline
119
(Scheme 4.35) [33]. Indeed, treatment of
119
with 5mol% of NaAuCl
4
in ethanol
furnished indole
in 76% yield. An additional four-step sequence was then
required to achieve the synthesis of (
120
)-mersicarpine
121
.
in the presence of a
catalytic amount of the gold complex (Ph
3
P)AuOTf (1mol%) leads to the formation
of the polycyclic enamine
The 7-
exo
-
dig
cyloisomerization of aminoalkyne
122
(Scheme 4.36). This transformation was used by
Crawley and Funk in a synthetic approach to the cytotoxic alkaloid communesin B
124
123
[34]. The enamine functionality could subsequently be used for the introduction
of the epoxide substituent at C11.
A fantastic example of an intramolecular alkyne hydroamination, which is
highly representative of the synthetic value of gold catalysis for the formation of
N
MeO
2
C
NaAuCI
4
·
2H
2
O
MeO
2
C
OH
4 step
s
(5 mol%)
ethanol, rt, 48 h
Et
Et
H
N
Et
NH
2
78%
HO
O
119
HO
120
(-)-Mersicarpine
121
SCHEME 4.35
Synthesis of (
)-mersicarpine by Fukuyama and coworkers.
O
CO
2
Me
CO
2
Me
H
HN
(Ph
3
P)AuOTf
(1 mol%)
CH
2
Cl
2
, 40°C, 12 h
N
N
11
H
H
N
O
11
NH
NH
89%
N
NH
N
H
H
N
H
122
123
Communesin B
124
SCHEME 4.36
Synthetic approach to the cytotoxic alkaloid communesin B by Crawley and
Funk.
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