Chemistry Reference
In-Depth Information
R
1
R
1
R
1
R
1
O O
110
N
N
N
N
F
2
+H
2
O+CH
3
CN
R
2
R
2
R
2
R
2
HOF
.
CH
3
CN
R
3
R
3
R
3
R
3
64
65a
:R
1
=R
2
=R
3
=H,60%
65b
:R
1
=R
2
=H, R
3
= Ph, 74%
65c
:R
1
=H,R
2
=R
3
=Me,67%
65d
:R
1
=Me,R
2
=H,R
3
=Ph,66%
Scheme 14
Synthesis of 1,10-phenanthroline 1,10-dioxides [
60
]
2.5
1,10-Phenanthroline 1,10-Dioxides
Oxidations of 1,10-phenanthrolines
64
to form 1,10-phenanthroline 1,10-dioxides
65
were found to be unsuccessful with a variety of oxidizing agents except with
HOF
.
CH
3
CN (Scheme
14
)
60
]. On the other hand, 5,6-dihydro-1,10-
phenanthrolines could be readily oxidized by a variety of oxidizing agents to
form the corresponding dioxides, which upon dehydrogenation could also produce
1,10-phenanthroline 1,10-dioxides. The presence of two oxygen atoms at the
sterically most hindered N1 and N10 positions could cause a helical twist of the
molecule. However, variable-temperature NMR studies with a chiral europium shift
reagent suggest a rapid rate of helix inversion on the NMR time scale.
3 Twisted Benzo[
c
]phenanthrenes and Related Compounds
3.1
1,12-Dialkylbenzo[
c
]phenanthrenes
The X-ray structure of benzo[
c
]phenanthrene (
66
) (Fig.
16
) shows significant
structural distortion [
61
]. The acute dihedral angle between rings A and C is
18.1
and between rings A and D is 26.7
. Placing one or two substituents at the
sterically most hindered C1 and C12 positions causes higher degrees of distortion.
The history of the chemistry of 1,12-dimethylbenzo[
c
]phenanthrene (
2
)resembles
that of 4,5-dimethylphenanthrene (
1
). The first synthesis of
2
was reported by
Newman and Wolf in 1952 [
9
]. The synthetic sequence included preparation of
diacid
67
for the Friedel-Crafts acylation reactions to form diketone
68
(Scheme
15
).
Reduction followed by dehydration and dehydrogenation then produced
2
.
Similarly, 1,12-dimethylbenzo[
c
]phenanthrene-5-acetic acid (
69
) (Fig.
17
) was
later synthesized and resolved [
62
]. However, unlike 4,5,8-trimethyl-1-phenanthre-
neacetic acid (
9a
), which undergoes rapid helix inversion at room temperature,
69
is
optically stable in refluxing mesitylene at 163
C for several days. The methyl ester
of
69
was also found to be optically stable at temperature up to 250
C for 30 min.
