Chemistry Reference
In-Depth Information
R
a
R
R
RLi
"E"
57
E
58
b
59a
:Ar=Ph,64%
a
59b
:Ar=
m
-NO
2
C
6
H
4
, 64%
a
59c
: Ar = 2-thienyl, 63%
a
59d
:Ar=2-furyl,70%
a
59e
:Ar=2-pyridyl,50%
b
a
ArB(OH)
2
,
b
ArSnBu
3
Bu
Bu
ArB(OH)
2
or ArSnBu
3
Pd(PPh
3
)
4
,DMF
I
58a
Ar
59
Scheme 18 (a) Synthesis of unsymmetrical dibenzo[
a,e
]pentalenes. (b) Metal-catalyzed cross-
coupling of vinyl iodide 58a [
91
]
a
O
Ar
1
O
H
Ar
1
Ar
1
R
R
R
4LiNaph
+
THF, rt
Ar
1
R
R
R
Ar
1
OH
Ar
1
O
60
61
62
b
Ph
Ph
OMe
OMe
1)
i
Bu
3
Al(TMP)Li
THF, -78 C
I
I
2) I
2
,0C
78%
MeO
MeO
Ph
Ph
62a
63
Ph
OMe
64a
:Ar
2
= Ph, 77%
64b
:Ar
2
= 3-Pyridyl, 73%
64c
:Ar
2
=C
6
F
5
,33%
i
Ar
2
Ar
2
MeO
Ph
64
Scheme 19 (a) Reductive double cyclization of
o
,
o'
-bis(arylcarbonyl)-diphenylacetylene 60 to
give methylene-bridged stilbene 61 and DAP 62.(b) Metal-catalyzed cross-coupling of 2,7-
diiodo-substituted DAP 63 [
92
]. Conditions: for 64a/b (i) ArB(OH)
2
,Pd
2
(dba)
3
CHCl
3
/S-Phos,
K
3
PO
4
, PhCH
3
/H
2
O or 1-butanol, for 64c (i) (1)
n
BuLi, THF
78
C, (2) C
6
F
6
,
78
Ctort
Similarly inspired by the reactivity of phenylacetylenes, Yamaguchi and
coworkers reported a new synthesis of DAPs and the closely related methylene-
bridged stilbene scaffold [
92
]. Treatment of
o,o
0
-bis(arylcarbonyl)-diphenyl-
acetylenes (60) with lithium naphthalide caused a two-electron reduction.
Calculations indicated that each radical anion resides at one of the carbonyl
positions, and thus the reduction is followed by a twofold radical 5-
endo-dig
cyclization onto the acetylene moiety to give the tetracyclic products (Scheme
19
a).
The authors determined that DAP 62 resulted from the over-reduction of 61 by
excess lithium naphthalide. Using the electron-rich 62a the authors are able to
iodinate the DAP at the C2/7 position, and then further extend the DAP through
metal-catalyzed cross-coupling (Scheme
19
b)
