Biomedical Engineering Reference
In-Depth Information
Hegedus and coworkers (1976)
Larock and coworkers (1998)
Pd(II), [H]
or
cat. Pd(II), Cu(OAc)
2
or benzoquinone
R
2
R
3
I
Pd(II)
base
LiCl or
n-
Bu
4
NCl
Me
H
R
2
NH
2
NHR
1
NR
1
R
3
Zhu and Jia (2006)
R
3
Pd(II),
L1
, base
X=I; ligandless
X=Br, Cl
X
R
3
R
2
R
2
NR
1
NHR
1
O
H
SCHEME 3.15
Indole synthesis by Hegedus, Larock, and Zhu.
H
N
Me
N
NHTr
O
O
NMe
Me
H
HO
Me
H
NH
H
H
NH
NH
(±)-Aurantioclavine
Hegedus (1987)
Arcyriacyanin A
Steglich (1997)
Costaclavine
Murakami (1999)
Ergot alkaloid tricyclic core
Rapoport (1999)
O
O
CO
2
t-
Bu
N
H
N
H
H
HN
NH
NBoc
2
O
HN
MeO
2
C
O
NH
O
O
O
N
H
2
N
Boc
R
1
HN
NH
O
H
N
H
CO
2
H
N
Central tryptophan core
Campagne and Michaux (2008)
Celogentin C
SCHEME 3.16
Selected indole ring-containing natural compounds.
3.2.6. C-S and C-O Bond Formation
Although many examples of C-N bond formation via Buchwald-Hartwig cross-
coupling have been published, only a few synthetic applications with oxygen and
sulfur as nucleophiles have been described so far. One example of carbon-sulfur
(C-S) bond formation was shown in the synthesis of griseoviridin's nine-membered
thiolactone core
, a streptogramin antibiotic, proposed by Campagne and Moreau
(Scheme 3.17) [41]. An intermolecular Pd-catalyzed thiol-vinyl iodide coupling
reaction gave rise to the expected vinyl sulfide
43
42
that in turn afforded
43
in 58%yield
after a Mitsunobu lactonization.
The total synthesis of (
)-murrayazoline, another carbazole alkaloid showing a
potent antiplatelet aggregation activity, has been recently reported by Chida and
coworkers [42]. The sequence is characterized by multiple Pd-assisted carbon-
heteroatom bond formation, including a dual
N
-arylation reaction of primary amine
45
and 2,2
0
-dibromobiphenyl derivative
44
, as well as an intramolecular etherification
of tertiary alcohol
47
(Scheme 3.18).
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