Chemistry Reference
In-Depth Information
BrCH
2
CH
2
Br
O
O
HO
OH
CH
2
Br
CH
2
Br
O
O
CH
2
Br
CH
2
Br
O
O
Cs
2
CO
3
O
O
BrCH
2
CH
2
Br
78
79
Scheme 29 Formation of Kuratowski-type aromatic network
O
N
NH
2
Zn
2+
or Cu
2+
6
+
6
H
H
N
N
NH
2
O
O
O
67
68
80
Scheme 30 One-pot synthesis of Borromean link network (see also Scheme
25
)
6.2 Other Topological Isomers
A few named topologically interesting molecules are introduced [
120
]. Multicyclic
compounds called Kuratowski cyclophanes have a nonplanar graph,
K
3,3
.Thisgraph
contains two sets of three points (units) and each in one set is connected to every point
in the other set, as illustrated in G in Scheme
2
. This topology was realized by
cyclization of compound 78 and 2,7-dihydroxynaphthalene (Scheme
29
)[
136
]. One
of the products was found to be Kuratowski-type cyclophane 79 of
D
2d
symmetry.
A Borromean link consists of three rings, where any of two rings are not
catenated to each other but the ring system is held together by the presence of the
third ring [
137
]. The construction of this complicated ring system would require
intelligent preorganization. One of the typical strategies is “ring-in-ring strategy,”
where a two-ring system with one ring threaded into another ring is used as a
template for the third ring formation. For example, Siegel et al. proposed a synthetic
approach with polypyridine templates, where diphenylterpyridine units worked as
template coordination sites as well as spacers to form a large internal space [
138
].
Regardless of such high-ordered topology, a molecular Borromean link could be
constructed by a one-pot process. Two precursors 67 and 68 used for the Solomon
link synthesis were treated with either Zn(II) ions or Cu(II) ions to form Borromean
link system 80 in high yield (Scheme
30
)[
139
]. The interlocked structure involving
three rings and six metal ions at the coordination sites was unambiguously con-
firmed by X-ray analysis.
