Biomedical Engineering Reference
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efficient (78-92%) and furnishes bicycloalkenones
175
through a selective 5-
endo
cyclization.
4.4.1.2. Intramolecular Hydroarylations of Alkynes When the “ene”
partner in an enyne cycloisomerization is part of an aromatic or a heteroaromatic
nucleus, the transformation is similar to a Friedel-Crafts reaction and can be seen as
an intramolecular hydroarylation of the alkyne moiety (Scheme 4.52).
Such transformation was used by Menon and Banwell to generate the bicyclic
core of the furanosesquiterpene crassifolone
180
(Scheme 4.53) [49]. The hydro-
arylation step was performed on ynone
using [(JohnPhos)Au(NCCH
3
)]SbF
6
as
the catalyst and furnished the desired bicyclic furan
178
179
in quantitative yield.
urstner and coworkers, on the other hand, used a polysubstituted pyrrole
nucleophilic partner in a gold-catalyzed hydroarylation to generate the tetracyclic
aromatic core of the dictyodendrin alkaloids (Scheme 4.54) [50].
F
€
R
2
R
2
R
2
Au(I) or Au(II
I
)
R
1
R
1
R
1
and/or
endo
-Hydroarylation
exo
-Hydroarylation
SCHEME 4.52
O
[(JohnPhos)Au(NCCH
3
)]
+
SbF
6
-
(1 mol%)
O
2 steps
O
O
O
O
CH
2
Cl
2
, rt, 0.08 h
100%
178
179
Crassifolone
180
SCHEME 4.53
Synthesis of crassifolone by Menon and Banwell.
OMe
MeO
OSO
3
Na
HO
OMe
NH
OMe
(Ph
3
P)AuCl (5 mol%)
NH
NH
MeO
2
C
OH
AgSbF
6
(5 mol%)
N
N
N
CH
2
Cl
2
, 0°C, 2 min
67%
OH
HO
OMe
MeO
OH
MeO
OMe
Dictyodendrin A
SCHEME 4.54
Gold-catalyzed hydroarylation to generate the tetracyclic aromatic core of
the dictyodendrin alkaloids by Furstner and coworkers.
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