The first synthesis of bis-fused 1,10-phenanthrolines via double photocyclization of N,N-disubstituted o-phenylenediamine

Article abstract of DOI:10.1055/s-2006-926441

Bis[1]benzothieno[2,3-c;3′,2′-i][1,10]phenanthroline was prepared in four steps starting from o-phenylenediamine with a double photocyclization as the key step to construct the 1,10-phenanthroline moiety. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-926441

1402
SHORT PAPER
The First Synthesis of Bis-Fused 1,10-Phenanthrolines via Double Photo-
cyclization of N,N-Disubstituted o-Phenylenediamine
B
is-Fused1,10-
a
Phenanthr
o
r
lines ek Abou Elmaaty, Lyle W. Castle*
Chemistry Department, Idaho State University, Campus Box 8023, Pocatello, ID 83209, USA
Fax +1(208)2824373; E-mail: castlyle@isu.edu
Received 28 November 2005; revised 19 December 2005
Previously, photocyclization reactions to generate the
Abstract: Bis[1]benzothieno[2,3-c;3¢,2¢-i][1,10]phenanthroline
was prepared in four steps starting from o-phenylenediamine with a
double photocyclization as the key step to construct the 1,10-
phenanthroline moiety.
1,10-phenanthroline moiety have been carried out in cy-
clohexane or benzene.2 Often the use of these solvents
would limit the quantity of material that could be reacted
(200–500 mg). Due to the extremely low solubility of the
amides in this work, we explored the use of DMF as a pho-
tocyclization solvent. It was found that using DMF as a
solvent allowed for the reaction to be scaled up (tenfold),
with excellent yields. Also, when using DMF the lactam
is obtained in high purity generating material that can be
used directly in the next step. The 1H NMR spectrum of 6
revealed two singlets at 9.38 and 9.83 ppm corresponding
to H-15/16 and H-6/9, respectively. A COSY spectrum
shows the expected four spin system corresponding to H-
1/14, H-2/13, H-3/12, and H-4/11. The doublet resonating
at 9.13 ppm, corresponding to H-1/14 correlates with the
multiplet at 7.80 ppm that corresponds to H-2/13 and H-3/
12. This multiplet correlates with the doublet resonating at
8.38 ppm corresponding to H-4/11. The 13C NMR spec-
trum shows resonances corresponding to the six CH car-
bons, however, due to the low solubility of 6, even after
an overnight run, none of the quaternary carbon resonanc-
es were observed. Finally, HRMS confirmed that the cy-
clization had occurred.
Key words: heterocycles, 1,10-phenanthrolines, photocyclization
Chelating agents such as 1,10-phenanthrolines have
gained importance as water-splitting agents, molecular
switches, and artificial nucleases (DNA cleavers).1 Re-
search in our laboratory has been centered around the syn-
thesis of new c-fused aromatic 1,10-phenanthrolines
using a photocyclization reaction to construct the skeleton
of the 1,10-phenanthroline moiety.2 This extends this re-
search area by generating 1,10-phenanthrolines that are
fused on both the c- and i-face (Figure 1).
c-face
i-face
N
N
1,10-Phenanthroline
Figure 1
In conclusion, we have presented the first synthesis of the
1,10-phenanthroline moiety via a double photocyclization
reaction. This method should be applicable to the synthe-
sis of other similar systems. This ring system is unique in
that it contains two bay regions and is a dipyridodithieno
analogue of the hitherto unknown dibenzo[a,o]picene ring
system.3
The key reaction involves a double photocyclization that
generates the 1,10-moiety in a single step. This method is
unique in that it generates a bis-fused 1,10-phenanthroline
ring system in one reaction. This method could be used to
generate compounds containing two or more 1,10-
phenanthroline moieties. Compounds of this nature will
be especially useful in the fields of organometallic poly-
mers and molecular switches.
All melting points were obtained in open capillary tubes and are un-
The synthesis of our target compound bis[1]ben- corrected. The 1H and 13C NMR spectra were determined on a Vari-
an Mercury 300 MHz FT NMR 300 with DMSO-d6 as solvent with
zothieno[2,3-c;3¢,2¢-i][1,10]phenanthroline (6) is accom-
chemical shifts reported in ppm relative to TMS as internal stan-
plished in four steps from known starting materials. In the
dard. Electrospray MS were carried out on a Waters Autospec Ulti-
first step, o-phenylenediamine (1) is reacted with 3-chlo-
ma Magnetic Sector MS. Microanalysis was performed in house
robenzo[b]thiophene-2-carbonyl chloride (2) to form the
diamide N,N¢-(1,2-phenylene)di-3-chlorobenzo[b]thio-
phene-2-carboxamide (3) which is photocyclized in DMF
using a Perkin Elmer Series II CHNS/O Analyzer 2400. Reagents
were purchased from Aldrich.
to form the bislactam 4. Reaction of 4 with POCl3 gener- N,N¢-(1,2-Phenylene)di-3-chlorobenzo[b]thiophene-2-carboxa-
mide (3)
ated the dichloro compound 5, which can be subjected to
3-Chlorobenzo[b]thiophene-2-carbonyl chloride (1; 2.3 g, 10
catalytic hydrogenation to form the target 6 (Scheme 1).
mmol) and o-phenylenediamine (2; 2.84 g, 20 mmol) were dis-
solved in benzene (50 mL) and were heated at reflux for 4 h. The
reaction mixture was allowed to cool to r.t., then the deposited solid
was collected by filtration and crystallized (EtOH) to give colorless
crystals; yield: 80%; mp 253 °C.
SYNTHESIS 2006, No. 9, pp 1402–1404
x
x
.
x
x
.2
0
0
6
Advanced online publication: 11.04.2006
DOI: 10.1055/s-2006-926441; Art ID: M08005SS
© Georg Thieme Verlag Stuttgart · New York

SHORT PAPER
Bis-Fused 1,10-Phenanthrolines
1403
Cl
NH2
Cl
benzene, Et3N
DMF
Cl
Cl
+
∆
S
O
S
hν
NH2
S
NH HN
2
1
O
O
3
POCl3
DMF
S
S
S
S
H2, Pd/C
KOH, MeOH
N
N
NH HN
Cl
Cl
O
O
4
5
2
13
12
11
3
4
1
14
9
15
16
S
S
10
5
N
8
N
7
6
6
Scheme 1
1H NMR (DMSO-d6): d = 7.38 (dd, J = 6.0, 4.5 Hz, 2 H), 7.62 (m,
4 H), 7.78 (dd, J = 6.0, 4.5 Hz, 2 H), 7.92 (d, J = 7.0 Hz, 2 H), 8.18
(d, J = 7.0 Hz, 2 H), 10.02 (s, 2 H NH).
1H NMR (DMSO-d6): d = 7.85 (m, 4 H), 8.40 (d, J = 7.5 Hz, 2 H),
9.16 (d, J = 7.5 Hz, 2 H), 9.42 (s, 2 H).
Anal. Calcd for C24H14Cl2N2S2: C, 61.94; H 3.03; N, 6.02. Found:
C, 61.90; H 2.81; N, 6.23.
Anal. Calcd for C24H14Cl2N2O2S2: C, 57.95; H 2.84; N, 5.63. Found:
C, 58.02; H 2.74; N, 5.99.
Bis[1]benzothieno[2,3-c;3¢,2¢-i][1,10]phenanthroline (6)
A mixture of 5 (0.23 g, 0.05 mmol), KOH (0.1 g), MeOH (20 mL),
DMF (300 mL), and 10% Pd/C (0.1 g) was hydrogenated at atmo-
spheric pressure at r.t. for 24 h. The catalyst was removed by filtra-
tion and the filtrate was evaporated to dryness in vacuo. The
residual solid was washed with H2O then filtered. The resulting sol-
id was crystallized (EtOH–DMSO) to give compound 6 as yellow
crystals; yield: 50%; mp > 300 °C.
1H NMR (DMSO-d6): d = 7.80 (m, 4 H), 8.38 (d, J = 7.2 Hz, 2 H),
9.13 (d, J = 7.2 Hz, 2 H), 9.37 (s, 2 H), 9.83 (s, 2 H).
13C NMR (DMSO-d6): d = 141.89, 128.91, 126.87, 126.62, 124.94,
124.02 (6 CH).
Bis[1]benzothieno[2,3-c:3¢,2¢-i][1,10]phenathroline-
6,9(7H,8H)dione (4)
A stirred solution of 3 (0.99 g, 2 mmol) was dissolved in DMF (200
mL) and placed in the photocyclization reaction vessel. To this so-
lution was added CHCl3 (600 mL) and Et3N (0.1 mL). The resulting
solution was irradiated with a 450-W Hanovia medium-pressure
mercury lamp for 72 h, while a slow stream of air was bubbled
through the solution. The precipitate was collected by vacuum fil-
tration, washed with H2O, and then air dried to yield 4 as yellow
powder; yield: 90%; mp > 300 °C. 1H NMR (DMSO-d6): d = 7.75
(m, 4 H), 8.32 (d, J = 7.8 Hz, 2 H), 8.81 (s, 2 H), 8.97 (d, J = 7.5 Hz,
2 H), 12.3 (br s, 2 H NH).
HRMS: m/z calcd for C24H13N2S2 [M + H]+: 393.0515; found:
393.0516.
Anal. Calcd for C24H12N2O2S2: C, 67.91; H 2.85; N, 6.60. Found: C,
67.30; H 2.59; N, 6.69.
Anal. Calcd for C24H12N2S2: C, 73.44; H 3.08; N, 7.14. Found: C,
73.39; H 2.87; N, 7.23.
6,9-Dichlorobis[1]benzothieno[2,3-c;3¢,2¢-i][1,10]phenanthro-
line (5)
A suspension of 4 (0.42 g, 1 mmol) in POCl3 (15 mL) was heated at
reflux for 24 h. The reaction was allowed to cool to r.t. and then Acknowledgment
poured slowly into ice (200 mL). The resulting liquid slurry was
The authors thank the NSF for the purchase of the NMR instrument
(grant no. 9980793) and Idaho State University and Fulbright Com-
mission of Egypt for providing expenses for T.A.E.
then stirred for 0.5 h and allowed to stand overnight. Vacuum filtra-
tion yielded a greenish-yellow solid, which crystallized from DMF
to give yellow crystals; yield: 85%; mp > 300 °C.
Synthesis 2006, No. 9, 1402–1404 © Thieme Stuttgart · New York

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T. A. Elmaaty, L. W. Castle
SHORT PAPER
(2) (a) Halverson, A. P.; Castle, L. W.; Castle, R. N. J.
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Synthesis 2006, No. 9, 1402–1404 © Thieme Stuttgart · New York