Chemistry Reference
In-Depth Information
Fig. 29
ORTEP drawing of
the crystal structure of
97
with hydrogen atoms omitted
for clarity [
76
]. Reprinted
with permission from [
76
].
Copyright (2007) American
Chemical Society
97
O
O
O
CCl
3
CO
2
H
O
4-
t
-butylcatechol
+
O
O
refluxing
toluene
98
, 17%
Scheme 21
Synthesis of pentahelicenebisbenzoquinone
98
[
88
]
derivative [
87
]. Condensation between 1,4-diethenylbenzene and
p
-benzoquinone
led to pentahelicenebisbenzoquinone
98
having oxygen atoms at C1 and C14
positions (Scheme
21
)[
88
]. These oxygenated derivatives show higher configu-
rational stability than the parent dibenzo[
c
,
g
]phenanthrene (
86
). The half-life for
racemization at 25
C is ca. 6 years. Enantiopure pentahelicenebenzoquinones have
likewise been synthesized [
89
,
90
].
5 Twisted Naphthalenes, Anthracenes, and Higher Acenes
Twisted naphthalenes, anthracenes, and higher acenes have been reviewed recently
[
8
]. Only a brief summary of representative examples is given in this section.
5.1 Highly Substituted Naphthalenes
Naphthalenes with eight substituents usually show twisted structures. The twist can
be attributed to nonbonded steric interactions between substituents on C1 and C8
and on C4 and C5. The distance between C1 and C8 in naphthalene is only 2.5
˚
,
which is invariably shorter than the sum of the van der Waals radii of the two
