Chemistry Reference
In-Depth Information
4.3 1,14-Dimethoxydibenzo[
c
,
g
]phenanthrene and Related Compounds . . . . . ........... 55
5 Twisted Naphthalenes, Anthracenes, and Higher Acenes ................................... 56
5.1 Highly Substituted Naphthalenes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
5.2 Highly Substituted Anthracenes . ...................................................... 57
5.3 Highly Substituted Higher Acenes ..................................................... 59
6 Conclusions and Outlook ..................................................................... 59
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
Abbreviations
[
] Specific rotation
Ar Aryl
Boc
tert
-Butoxycarbonyl
CD Circular dichroism
DMF
N
,
N
-Dimethylformamide
Et Ethyl
HPLC High-performance liquid chromatography
i
-Pr
a
Isopropyl
LDA
Lithium diisopropylamide
Me
Methyl
n
-Bu
Normal (primary) butyl
NMR
Nuclear magnetic resonance
Ph
Phenyl
p
-Ts
para
-Toluenesulfonyl
t
-Bu
tert
-Butyl
UV
Ultraviolet
VPO
Vapor pressure osmometry
1
Introduction
Twisted arenes have attracted the attention of chemists for more than 70 years [
1
,
2
].
It was readily recognized that the structure of 4,5-dimethylphenanthrene (
1
)is
distorted due to nonbonded steric interactions of the two methyl groups occupying
the crowded C4 and C5 positions (Fig.
1
)[
3
-
5
]. Although the nature of the
distortion was not apparent initially, bending the methyl groups away from each
other and/or twisting the aromatic framework were considered as possible ways to
relieve some of the strain. The X-ray structure of
1
now clearly indicates the
presence of a significant helical twist in the phenanthrene system [
5
-
7
]. It has
also been well established that the energy required to twist a polycyclic aromatic
hydrocarbon is quite modest [
8
], and many examples of twisted arenes are known
with some showing remarkable degrees of distortion.
In addition to
1
and the related phenanthrene systems, placing two substituents at
the crowded C1 and C12 positions of benzo[
c
]phenanthrene, such as 1,12-
dimethylbenzo[
c
]phenanthrene (
2
)[
9
,
10
], also causes a significant twist of the
