Biomedical Engineering Reference
In-Depth Information
TosHN
OTBS
S
S
1.
169
, -78°C to -25°C
S
Li
S
2.
170
, HMPA, Et
2
O
-78°C to 0°C, 5 h
TMS
OTBS
168
171
O
OTBS
169
NTos
H
H
170
N
N
H
H
(-)-Indolizidine 223AB
172
Alkaloid (-)-205B
173
SCHEME 9.29
Synthesis of indolizidine 223AB
172
by Smith and coworkers.
intermediate
177
through an aldol condensation affords the desired
trans
-decalin core
178
in excellent yield. This highly efficient domino process culminating in the
formation of three newC-C bonds is used as part of a stereoselective total synthesis of
the natural product in 18 steps and 5% overall yield.
Strychnine (
) isolated from the seeds of
Strychnos nuxvomica
has been
used as a fatal poisoning agent throughout history. This strychnos-type alkaloid
attracted much attention because of its complex ring system and was later used as a
pesticide. The stereoselective construction of similar enantiopure indole tetra-
cycles via a domino reaction was initially developed by Kuehne et al. [71] In the
central point of this synthetic study, the enantiopure tryptophan
185
180
was initially
treated with
a
,
b
-unsaturated aldehyde
181
and following condensation and
cyclization,
the intermediate
182
is assumed to form. Subsequent Cope
NaOMe
MeOH, 50°C
O
O
O
CO
2
Me
+
I
MeO
OMe
OMe
82%
174
175
MeO
2
C
OMe
O
176
O
O
OAc
H
H
H
O
steps
O
CO
2
Me
CO
2
Me
O
MeO
OMe
MeO
OMe
O
(-)-Tanabalin
179
178
177
SCHEME 9.30
Synthesis of tanabalin
179
by Watanabe and coworkers.
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