Chemistry Reference
In-Depth Information
O
O
B
B
O
O
O
Br
B
PdCl
2
(dppf)/KOAc
O
68%
Br
102
103
Pd(PPh
3
)
4
,
Na
2
CO
3
Br
104
13%
105
Scheme 24 Example for a Pd-catalyzed cross coupling reaction for the synthesis of a
trisanthracene 105 [
63
]
R
R
R
R
R
R
Suzuki reac
t
ion
FeCl
3
I
X
I
X
Y
Y
R
R
106
R
R
R
R
107
108
R = H, Alkyl, phenylalkyl
X, Y = H, Halogen, Alkyl
Scheme 25 Suzuki cross-coupling reaction for the preparation of a
para
-substituted HBC
108 [
64
]
Similarly, a Suzuki reaction was applied to access the hexaphenylbenzene
derivative 107 with two different substituents in
para
position. Dehydrogenation
delivered the
para
-substituted HBC 108 [
64
].
2.4.2 Cross-Coupling Reactions Involving C-H Bond Activation
More recently, direct C-H functionalization has been developed [
65
] and also
applied to the assembly of large aromatic structures [
66
]. The preparation involving
C-H bond activation offers the great advantage that no pre-functionalization of the
reaction partners is necessary. However, in most cases a suitable coordinating group
must be present, limiting the application for the preparation of non-functionalized
graphene-type structures [
67
]. In Scheme
26
a recent example has been presented,
where a tethered aromatic C-H bond is connected via Pd-catalysis [
68
]. The
immediate aromatization under acidic condition delivers the final PAH 111.An
example
starting from bromostilbenes using Pd-catalysis has
also been
reported [
69
].
