Chemistry Reference
In-Depth Information
H
N
N
N
MeO
MeO
MeO
Me
TfOH
BnO
O
O
CCl
4
, -5
°
C
MeO
N
3
MeO
NH
2
MeO
OMe
212
213
(81%)
(+)-Cularine (
214
)
SCHEME 10.32.
213
and subsequently establish the dihydrooxepine skeleton of
with complete
regiocontrol.
In reference to the formation of carbocycles via aryl nitrenium ion cyclization, upon
exposure to a mixture of triflic and trifluoroacetic acids, 3-phenethylbenzene azides,
such as
215
, undergo intramolecular aromatic substitution to form 9,10-dihydrophe-
nanthrene derivatives
withmoderate regioselectivity (Scheme 10.33).
75,81
In a more complex setting, Abramovitch has utilized this transformation to generate
the aporphine ring system
216
and
217
.
82
In subsequent studies, Abramovitch demonstrated that medium-sized carbocycles
are also accessible through the intramolecular cyclization of aryl nitrenium ions.
83
Thus, upon treatment with triflic acid, azide
220
from tetrahydroisoquinoline
218
underwent intramolecular aromatic
substitution to provide aminodibenzo[
a
,
c
]octatriene
221
224
, after rearomatization of
dienimine
(Scheme 10.34). Significantly, lower yields were obtained for a
substrate lacking the
223
a
,
b
-unsaturated ester moiety; a fact which Abramovitch,
N
3
H
2
N
TfOH (cat.)
+
TFA, 0°C
NH
2
215
216
(73%)
217
(15%)
MeO
MeO
MeO
N
N
TfOH (cat.)
N
MeO
Me
MeO
Me
MeO
Me
+
TFA, 0°C
H
2
N
NH
2
N
3
218
219
(14%)
220
(27%)
SCHEME 10.33.
