Chemistry Reference
In-Depth Information
Ph Ph
O
O
R
R
2
32a
/
n
-BuLi
t
-Bu
t
-Bu
t
-Bu
t
-Bu
82
83
: R = OH, 95%
Et
3
SiH
CF
3
CO
2
H
84
:R=H, 80%
Ph
Ph
KO
t
-Bu
refluxing
toluene
A
D
t
-Bu
t
-Bu
85
,10%
Scheme 17
Synthesis of diindeno-fused 1,12-diphenylbenzo[
c
]phenanthrene
85
[
76
]
Fig. 24
ORTEP drawing of
the crystal structure of
85
with hydrogen atoms omitted
for clarity [
76
]. Reprinted
with permission from [
76
].
Copyright (2007) American
Chemical Society
85
4 Twisted Dibenzo[
c
,
g
]phenanthrenes and Related Compounds
4.1
1,14-Dialkyldibenzo[
c
,
g
]phenanthrenes
The X-ray structure of dibenzo[
c
,
g
]phenanthrene (pentahelicene,
86
) shows a
pronounced structural distortion with a C14a-C14b-C14c-C14d torsional angle
of 32
and an acute dihedral angle between the mean planes of the two outer
benzene rings (rings A and E) of 50.6
(Fig.
25
)[
77
]. The activation barrier for
racemization is 24.1 kcal/mol at 40
C[
78
]. The half-life for racemization is ca. 14 h
