Arylbenzo[h][1, 6]naphthyridine derivatives: Synthesis and photophysical properties

Article abstract of DOI:10.1007/s10895-011-0850-2

Suzuki-Miyaura cross coupling was successfully used for C5-arylation in 4-amino-2-chloroquinoline-3-carbaldehyde using arylbornic acid and tetrakistriphenylphosphine palladium catalyst in water. Friedlaender condensation reaction on 4-amino-2-chloro/2-ary

Full text of DOI:10.1007/s10895-011-0850-2

J Fluoresc (2011) 21:1617–1624
DOI 10.1007/s10895-011-0850-2
ORIGINAL PAPER
Arylbenzo[h][1, 6]naphthyridine Derivatives:
Synthesis and Photophysical Properties
Raghunath B. Toche & Ravindra A. Janrao &
Sandeep M. Bagul & Shivaraj P. Patil &
Balasaheb P. Pagar & Prashant S. Nikam
Published online: 8 February 2011
#
Springer Science+Business Media, LLC 2011
Abstract Suzuki-Miyaura cross coupling was successfully
used for C5-arylation in 4-amino-2-chloroquinoline-3-carbal-
dehyde using arylbornic acid and tetrakistriphenylphosphine
palladium catalyst in water. Friedländer condensation reac-
tion on 4-amino-2-chloro/2-arylquinoline-3-carbaldehyde
and aromatic ketones gave novel aryl and diarylbenzo[h]
[1, 6]naphthyridines in good yields. Fluorescence quantum
yields were increased by introducing C2 and C5 π donor
aryl benzo[h][1, 6]naphthyridines derivatives.
π-donor-acceptor conjugated system connected finally by
single bond. The charge transfer excited states are the cause
of induced photo physical properties of the molecule. The
widely accepted proposals explaining photo physical
properties are TICT (twisted intermolecular charge transfer)
state model [1–3] and push pull mechanism [4, 5] of donor-
aceptor auxochromes and chromophores. The perpendicular
geometry was the question recently arise as an inherent
precondition to obtained intramolecular charge transfer in
such systems [6–8] The nonlinear molecules possessing
optical properties showing transitions from electronics to
photonics are the required materials [9] for potential
applications in optical data storage, telecommunications
and optical signal processing and optical switching [10–17].
The fused heterocyclics are rigid and stable systems possess
high heat and photochemical stability, are suitable material
for optoelectronic devises. The hetero atoms in the
molecule act as an auxiliary donor-acceptor to increase
fluorescence quantum yields through push pull mechanism
[18, 19]. We have reported [20–23] the synthesis and
fluorescent properties of dipyrazolo[3,4-b:3,4-d]pyridines
(DPP), pyrazolo[3,4-b]pyrrolo[2,3-d]pyridines (PPP) and
pyridine-3-carbonitriles. It was observed that the fluores-
cent properties of these candidates are depending upon the
nature of donor-acceptor substituents on the C4-aryl, also
causes for the perpendicular geometry for TICT state. This
paper report the Suzuki–Miyaura cross coupling on 4-
amino-2-chloroquinoline-3-carbaldehyde to form 4-amino-
2-arylquinoline-3-carbaldehyde i.e. C2-arylation without
protection of other groups, which were used to prepare 5-
chloro-2-arylbenzo[h][1, 6]naphthyridines 8(a-d) and 2,5-
diarylbenzo[h][1, 6]naphthyridines 9(a-h) and further study
of their fluorescence properties.
.
Keywords Benzo[h][1, 6]naphthyridines Fluorescence
.
.
quantum yields Suzuki-Miyaura cross coupling reaction
.
Friedländer condensation reaction
Tetrakistriphenylphosphine
Introduction
Photoinduced intramolecular electron transfer processes are
playing important role in importing photo physical and
photo chemical properties to organic molecules constituting
:
:
:
:
R. B. Toche (*) R. A. Janrao S. M. Bagul S. P. Patil
:
B. P. Pagar P. S. Nikam
Organic Chemistry Research Center, Department of Chemistry, K.
R. T. Arts, B. H., Commerce and A. M. Science College,
Gangapur Road,
Nashik 422002 MS, India
e-mail: raghunath_toche@rediffmail.com
:
:
:
:
R. B. Toche R. A. Janrao S. M. Bagul S. P. Patil
:
B. P. Pagar P. S. Nikam
University of Pune,
Pune-07, India

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J Fluoresc (2011) 21:1617–1624
Results and Discussion
Photo Physical Properties
Sylvain Rault and co-workers [24] have been reported the
synthesis of benzo[h][1, 6]naphthy- ridines analogues via
rearrangement of hexahydro-5 H-pyrrolo[2,1-c][1, 4] ben-
zodiazepines in 12% yield. We have obtained 5-chloro-2-
arylbenzo[h][1, 6] naphthyridines 8(a-d) and 2,5-diary-
lbenzo[h][1, 6]naphthyridines 9(a-h) 60–85% yields.
4-Amino-2-oxo-1,2-dihydroxyquinoline-3-carboxylate
[25] 2 was obtained by cyclocondensation of diethylmal-
onate and 2-cyanoaniline 1 in basic medium. The
chlorination of this compound with phosphorousoxychlor-
ide at reflux temperature yielded ethyl 4-amino-2-chlor-
oquinoline-3-carboxylate 3 in 76% yield, which on LAH
reduction furnish 4-amino-2-chloroquinolin-3-yl) metha-
nol 4 in 87% yield.
Compound 4 on MnO2 oxidation afforded required
synthon 4-amino-2-chloroquinoline-3-carbaldehyde 5 in
73% yields (Scheme 1). The structures of compounds 3, 4
and 5 were confirmed by spectroscopic characterization
data. For instance, IR spectrum of 5 showed stretching for
NH2 at 3293, 3261 cm-1 and CHO at 1719, 2705 cm.-1 The
1H NMR in DMSO-d6 showed NH2 protons splited in two
broad singlets at δ 8.97 and δ 9.87 (D2O exchangeable) due
to the intramolecular hydrogen bonding between CHO and
NH2 group. The highly deshielded aldehydic proton was
observed at δ 10.30 and the rest of aromatic protons
appeared at δ 7.60–8.46. The mass spectrum and elemental
analysis also match with the proposed structure of 5.
Friedländer condensation on 4-amino-2-chloroquinoline-3-
carbaldehyde 5 with substituted aromatic ketones (7a-d) in
ammonium acetate as green solvent and reagent at 120oC
furnished 5-chloro-2-aryllbenzo[h][1, 6]naphthyridine (8a-d)
in 65–80% yields (Scheme 1).
The photophysical study of benzo[h][1, 6]naphthyridines
8 showed C2-aryl dependent fluorescence quantum yields.
The presence of auxochrome (donor) on C2-aryl increases
while chromophore (acceptor) on C2-aryl decreases the
absorption and emission λmax. This observation inspired us
to study the substituent effect at C5-aryl of this molecule.
For C5-arylation after trying by several methods, the
Suzuki-Miyaura cross-coupling reaction [26–29] gave sat-
isfactory results because its mild reaction conditions
required here due to presence of active functional groups.
The tetrakistriphenylphosphine palladium as a heteroge-
neous catalyst in water and 1,2-dimethoxyethane co-solvent
in 3.5: 3 mL gave 4-amino-2-arylquinoline-3-carboalde-
hyde 6 in 82–87% yield. Interestingly, this one pot reaction
did not need the protection of CHO and NH2 group.
Further, the Friedlander reaction on compound 6 with
aromatic ketones in ammonium acetate, furnished diary-
lbenzo[h][1, 6]naphthyridines (9a-h) in 65–82% yields
(Scheme 2, Table 1).
The benzo[h][1, 6]naphthyridines 8(a-d), 9(a-h) are
colorless solids. The photo physical properties of these
compounds were determined with respect to quinine
sulphate as reference standard, using 0.1 mg/ml solution
in chloroform shows UV absorption and fluorescence
emission in the range of 343–390 nm and 415–498 nm
respectively (Table 1). In series of arylbenzo[h][1, 6]
naphthyridines 8(a-d) the strong π-donor aryl on C2-
position shows large bathochromic shift of absorption and
emission with low stoke’s shift, and high quantum yields
(Table 1, entry 8b, 8c).
For instance, compound 8c, having C2-(2,4,6-tri-OCH3)
Ph shows λMax=381 nm, λFlu=480nm, stock shift at
5,564 cm-1 and ΦF=0.24 (Table 1, Entry 3), while strong
acceptor C2 (4-NO2Ph) in compound 8d shows λMax=343,
λ
Flu=446nm, stock shift=7,840 cm-1 and ΦF=0.18 (Table 1,
entry 4). i.e. In arylbenzo[h][1, 6]naphthyridines 8 the C2-
donar shows increase while C2-acceptor on shows decrease
in the fluorescence quantum yields. Interestingly, introduc-
tion of C5-phenyl shows decreasing of photo physical
properties, but C5-(4-OCH3Ph) and C5-(4-NO2Ph) shows
large to moderate increase in fluorescence properties. e.g.
Compounds 9(a-c) having C5-Ph show lower absorption
in the range of 345–3,364 nm, emission 415–446 nm and
quantum yield ΦF=0.15–0.19 as compared with com-
pounds 8(a-c), which showed absorption in the range of
360–381 nm, emission 460–480 nm and quantum yield
ΦF=0.019–0.24. The push pull mechanism of donor
OCH3, and SP2 ‘N’ and twisting of C2 and C5-aryl
auxochromes in 9(d-f) or chromphores in 9(g-h) of benzo
[h][1, 6]naptharidines showed increase in fluorescence
properties. Auxochromes and chromophores both groups
help to increase absorption and emission as compared
with H on C5-Ph (Fig. 1)
Semi-Empirical Study of Benzo[h][1, 6]napthyridine
Derivatives 8, 9
The TICT and push pull mechanism of donor-acceptor
chromophores, affect the electronic transitions in the
molecule, these electronic transition import the fluorescence
properties to the molecule. The physical parameters
HOMO-LUMO, energy, ionization potential, heat of for-
mation are useful parameters to predict photophysical
properties and are calculated theoretically by using PM6
model [30, 31]. It was observed that compounds having
low HOMO-LUMO gap showed higher absorption and
emission wave length and hence showed high fluorescence
or quantum yields. e.g. compound 8c, having absorption
381 nm, emission 480 nm and quantum yields φF=0.24

J Fluoresc (2011) 21:1617–1624
1619
Scheme 1 Synthesis of
Arylbenzo[h][1, 6]naphthyridine
derivatives
NH2
O
O
NH2
O
CN
NaOEt / EtOH
reflux, 12 h
POCl3
O
O
CH2(COOEt)2
+
reflux, 5h
NH2
N
H
N
Cl
1
3
2
LAH/THF
rt, 4h
R3
R4
R5
R2
R5
O
R1
NH2
NH2
R4
NH4OAc
MnO2 / DCM
rt, 12h
N
O
OH
+
R3
R1
120 °C, 30 min.
N
Cl
N
Cl
R2
N
Cl
5
4
7a-d
8a-d
have lowest HOMO-LUMO gap=7.284. Similarly, in case
of 2, 5-diarylbenzo[h][1, 6]naphthyridines 9f, having higher
absorption 390 nm and emission 498 nm maxima and
quantum yield φF=0.26 showed lowest HOMO-LUMO
gap=7.068. The high heat of formation and ionization
potential showed high thermal stability, which indicate that
these compounds are suitable candidates for photo elec-
tronic devices.
Experimental
General
Melting points were determined on a Barnstead Electro
Thermal melting point apparatus, Mod. No. IA-9200 in
open capillary tubes and are uncorrected. The H NMR
1
(300 MHz) and 13C NMR (75 MHz) spectra were recorded
on Varian XL-300 spectrometer. Chemical shifts were
reported in ppm from internal tetramethylsilane standard
and are given δ-unit. The solvent for NMR spectra was
deuterio-chloroform unless otherwise stated. Infrared spec-
tra were taken on Shimadzu IR-408, instrument in
potassium bromide pellets unless otherwise stated. UV
spectra were recorded on a Shimadzu UV-1601 UV–VIS
Spectrophotometer. Fluorescence spectra were recorded
using RF-5301 PC Spectrofluorophotometer, compounds
for UV and fluorescence measurements were dissolved in
chloroform. UV and fluorescence scan were recorded from
200 to 600 nm. Elemental analyses were determined using
Thermo Quest Model No. flash EA 1112-Elemental
Analyzer within 0.3 of the theoretical percentage. High-
resolution mass spectra were obtained with a Mat 112
Varian Mat Bremen (70eV) mass spectrometer. Column
Conclusion
The C2-arylation was carried out by Suzuki–Miyaura cross
coupling under mild reaction conditions without protection
to active functional groups in presence of tetrakistriphenyl-
phosphine palladium as a heterogeneous catalyst in aqueous
medium. Friedländer condensation in ammonium acetate
yield novel aryl and diarylbenzo[h] [1, 6]naphthyridines in
good yields. Arylbenzo[h][1, 6]naphthyridines with C2-π-
donor and C5-π-donor-acceptor fluorophores to aryl
showed large bathochromic shift of absorption and emis-
sion with low Stoke’s shift, and high quantum yields, while
π-acceptor on C2-aryl chromophores shows hypsocromic
shift of absorption and emission properties.
R3
Scheme 2 Synthesis of
Di-arylbenzo[h][1, 6]naphthyri-
dine derivatives
R4
R5
R2
R1
NH2
N
R5
O
B(OH)2
Pd(PPh3)4,
K2CO3
R4
R3
N
N
O
NH4OAc
+
5
+
R1
water/DME
60 °C, 6h
120 °C, 30 min.
R2
R
R
6a-c
7a-d
R
9a-h
6a R= H
6b R = P-OMe
6c R = p-NO2

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J Fluoresc (2011) 21:1617–1624
Table 1 The photophysical data for electronic absorption (UVλMax), fluorescence (EmλMax) and quantum yield (φF) of compounds 8 and 9 in
CHCl3 at room temperature
Entry
Compd
R
7a-d
R1
λAbs. CHCl3
λFlu. CHCl3
Epsilon ε cm-1
ΦF
R2
R3
R4
R5
1
8a
8b
8c
8d
9a
9b
9c
9d
9e
9f
–
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
345
377
381
343
345
358
364
366
388
390
366
376
460
475
480
446
415
425
446
460
481
498
460
471
7,288
6,640
5,564
7,840
6,279
5,479
8,695
7,544
4,607
4,725
7,544
5,884
0.19
0.22
0.24
0.18
0.15
0.18
0.19
0.19
0.22
0.26
0.18
0.21
2
–
H
OCH3
OCH3
NO2
H
OCH3
H
H
3
–
OCH3
H
OCH3
H
4
–
H
5
H
H
H
H
5
H
H
OCH3
OCH3
H
OCH3
H
H
7
H
OCH3
H
OCH3
H
8
OCH3
OCH3
OCH3
NO2
NO2
H
9
H
OCH3
OCH3
OCH3
OCH3
OCH3
H
H
10
11
12
OCH3
H
OCH3
H
9g
9h
OCH3
H
OCH3
OCH3
chromatography was carried out on silica gel (SD Fine
Chemicals, 100–200 mesh). Solutions were concentrated in
a rotary evaporator under reduced pressure. All reactions
were monitored by thin layer chromatography (TLC),
carried out on 0.2 mm silica gel 60 F254 (Merck) plates
using UV light (254 and 366 nm) for detection. Common
reagents-grade chemicals are either commercially available
and were used without further purification or prepared by
standard literature procedures.
aqueous solution was extracted with CH2Cl2 (100 mL×2),
dried over sodium sulphate and concentrated to yield crude
solid, which was further purified by FC (using 20%
CH2Cl2/petroleum ether as an eluent) to give compound
3. Yield: 4.1 g (76.1%), yellowish white solid, mp. 197–
1
199 °C; IR (KBr): 3376, 3263, 1673, 1614, 767 cm.-1; H
NMR (DMSO-d6) δ: 1.47 (t, 3 H, J=7.2 Hz, OCH2CH3),
4.48 (q, 2 H, J=7.15 Hz, OCH2CH3), 6.83 (bs, 2 H, NH2),
7.51–7.88 (m, 4 H, ArH). 13C NMR (DMSO-d6) δ: 13.8,
61.3, 103.8, 117.2, 123.1, 125.5, 127.6, 131.7, 146.3,
147.2, 152.6, 165.7. MS m/z (%): 251.1 (M+1) (100),
253.1 (M+2) (20). Anal. Calcd for C12H11ClN2O2
(250.68): C, 57.50; H, 4.42; N, 11.17%. Found:C, 57.32;
H, 4.53; N, 11.18%.
Ethyl 4-amino-2-oxo-1,2-dihydroxyquinoline-3-carboxylate
22
(2) Yield: 41%. M.p.: 269–270 °C [Lit. Mp 269 °C]
Ethyl 4-amino-2-chloroquinoline-3-carboxylate (3) A mix-
ture of compound 2 (21.55 mmol, 5.0 g) in POCl3 (50 mL)
was refluxed for 5 h. (TLC monitoring, CH2Cl2/MeOH
10:1). After cooling the reaction mixture was slowly poured
in ice water (250 mL) and neutralized with NH4OH. This
4-Amino-2-chloroquinolin-3-yl-methanol (4) Add dropwise
solution of compound 3 (16.00 mmol, 4.0 g) dissolved in
dry THF (10 mL), in the flask flushed with nitrogen
Table II The molecular
Compd
Heat of formation (K cal.)
Ionization potential
HOMO
LUMO
GAP
electronic properties, HOMO-
LUMO energy gap of benzo [h]
[1, 6]naphthyridines 8 and 9
8a
8b
8c
8d
9a
9b
9c
9d
9e
9f
92.03
9.316
9.066
8.569
9.616
9.111
8.479
8.863
8.979
8.407
8.621
9.181
8.914
-9.317
-9.066
-8.570
-9.617
-9.111
-8.479
-8.864
-8.980
-8.407
-8.621
-9.181
-8.914
-1.301
-0.842
-1.286
-1.789
-1.048
-0.992
-0.601
-0.919
-0.948
-1.553
-1.381
-1.038
8.016
8.224
7.284
7.828
8.063
7.487
8.263
8.061
7.459
7.068
7.800
7.876
-32.30
15.55
-230.93
123.69
47.49
-0.111
-148.09
7.911
42.41
9 g
9 h
-5.603
8.411

J Fluoresc (2011) 21:1617–1624
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Fig. 1 Fluorescence spectra
of compounds 8 and 9
respectively
containing LAH (48.00 mmol, 1.8 g) in a dry THF (15 mL)
at 10–15 °C. The reaction mixture was stirrer at room
temperature for 4 h (TLC monitoring, CH2Cl2/MeOH
10:2). It was quenched by dropwise addition of saturated
sodium sulphate solution (20 mL) at room temperature
(COUTION-EXOTHERMIC). This aqueous mixture was
extracted with EtOAc (100 ml×2), dried over sodium
sulphate, and concentrated to yield pure compound 4.
Yield: 2.6 g (87.1%), white solid, mp. 185–187 °C; IR
(KBr): 3490, 3424, 3343, 1617,cm.-1; 1H NMR (CDCl3) δ:
4.74 (d, 2 H, J=6.0 Hz, CH2), 5.0 (t, 1 H, J=5.4 Hz, OH),
7.00 (bs, 2 H, NH2), 7.41–7.65 (m, 4 H, ArH). 13C NMR
(DMSO-d6) δ: 57.4, 109.6, 118.1, 122.4, 124.4, 127.7,
129.9, 146.5, 151.0, 152.3. MS m/z (%): 209.0 (M+1)
(100), 211.0 (M+2) (25). Anal. Calcd. for C10H9ClN2O
(208.64): C, 57.57; H, 4.35; N, 13.43%. Found: C, 57.41;
H, 4.43; N, 13.45%.
tetrakistriphenylphosphine palladium (0.70 mmol), K2CO3
(28.0 mmol) and appropriate arylboronic acid (18.2 mmol)
in water: DME (3.5:3 mL) were added sequentially. The
reaction mixture was heated to 60–65 °C temperature for 5-
6 h (TLC monitoring, CH2Cl2/MeOH 9:1). After completion
of reaction, the solid catalyst was filtered out, washed with
diethyl ether. The aqueous solution was then extracted with
diethyl ether (50 mL×3). The ether layer was dried over
anhydrous sodium sulphate and then evaporated under
reduced pressure; the residue was chromatographed over
silica gel column and eluted with chloroform-methanol (9.5:
0.5) to isolate the pure product.
4-Amino-2-phenylquinoline-3-carbaldehyde (6a) Yield:
2.8 g (82%), off white solid, mp. 201–203 °C. IR
(KBr): 3444, 3307, 2769, 1710 cm.-1; 1H NMR (DMSO-
d6) δ: 7.49–7.58 (m, 5 H, Ar-H), 7.76-7.85 (m, 4 H,
ArH), 8.68 (bs, 1 H, NH2), 9.70 (bs, 1 H, NH2), 9.79 (s,
1 H, CHO). 13C NMR (DMSO-d6) δ: 106.8, 117.5, 123.3,
125.2, 128.0, 128.0, 128.6, 129.2, 129.8, 129.8, 132.4,
138.9, 139.8, 147.8, 154.7, 163.2. MS m/z (%): 249.1
(M+1) (100). Anal. Calcd. For C16H12N2O (248.28): C,
77.40; H, 4.87; N, 11.28%. Found: C, 77.21; H, 4.95; N,
11.03%.
4-Amino-2-chloroquinoline-3-carbaldehyde (5) In the solu-
tion of compound 4 (12.5 mmol, 2.6 g) in dry DCM
(20 mL) was added MnO2 (3.5 g) and the reaction mixture
was stirred at room temperature for 12 h. (TLC monitoring
CH2Cl2/MeOH, 9:1). The MnO2 was filtered, washed with
DCM and then evaporating under reduced pressure. The
obtained solid was recrystallized from EtOAc to yield title
compound 5. Yield: 2.1 g (73.3%), off white solid, mp.
4-Amino-2-(4-methoxyphenyl)quinoline-3-carbaldehyde
1
278–280 °C; IR (KBr): 3293, 3261, 2705, 1719 cm.-1; H
(6b) Yield: 3.4 g (87%), brownish solid, mp. 176–178 °C;
1
NMR (CDCl3) δ: 7.60–7.84 (m, 4 H, ArH), 8.97 (bs, 1 H,
NH2), 9.87 (bs, 1 H, NH2), 10.3 (s, 1 H, CHO). 13C NMR
(DMSO-d6) δ: 104.5, 118.3, 123.8, 126.0, 128.2, 133.2,
146.9, 152.6, 156.2, 191.6. MS m/z (%): 207.1 (M+1)
(100), 209.0 (M+2) (20). Anal. Calcd. for C10H7ClN2O
(206.63): C, 58.13; H, 3.41; N, 13.56%. Found: C, 58.28;
H, 3.27; N, 13.75%.
IR (KBr): 3452, 3310, 2780, 1715, 1603 cm.-1; H NMR
(DMSO-d6) δ: 3.83 (s, 3 H, OCH3), 7.05 (d, 2 H, J=9.0 Hz,
ArH), 7.51 (d, 2 H, J=9.0 Hz, ArH), 7.62–8.46 (m, 4 H,
ArH), 8.62 (bs, 1 H, NH2), 9.54 (bs, 1 H, NH2), 9.83 (s,
1 H, CHO). 13C NMR (DMSO-d6) δ: 55.2, 106.8, 113.4,
113.4, 117.4, 123.3, 124.9, 129.1, 131.1, 131.4, 131.4,
132.3, 148.0, 154.7, 159.6, 162.7, 192.5. MS m/z (%):
279.1 (M+1) (100), Anal. Calcd for C17H14N2O2 (278.31):
C, 73.37; H, 5.07, N, 10.07%. Found: C, 73.54; H, 4.96, N,
10.21%.
4-Amino-2-phenylquinoline-3-carbaldehyde (6a-c) In a
flask flushed with nitrogen, compound 5 (2.90 g, 14.0 mmol),

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J Fluoresc (2011) 21:1617–1624
4-Amino-2-(4-nitrophenyl)quinoline-3-carbaldehyde (6c)
Yield: 3.5 g (85%), pale yellowish prism, mp. 181-182 °C;
IR (KBr): 3481, 3284, 2701, 1649, 1530, 1332 cm.-1; 1H NMR
(DMSO-d6) δ: 7.54 (d, 2 H, J=8.2 Hz, ArH), 7.97 (d, 2 H, J=
8.2 Hz, ArH), 8.34–8.48 (m, 4 H, Ar-H), 8.52 (bs, 1 H, NH2),
9.54 (bs, 1 H, NH2), 9.80 (s, 1 H, CHO). 13C NMR (DMSO-
d6) δ: 101.2, 117.2, 122.9, 122.9, 123.0, 125.6, 128.9, 129.2,
129.2, 131.6, 146.7, 149.4, 153.4, 157.4, 167.8, 192.5. MS m/
z (%): 294.08 (M+1) (100). Anal. Calcd for C16H11N3O3
(293.28): C, 65.53; H, 3.78; N, 14.33%. Found: C, 65.59; H,
3.82; N, 14.29%.
OCH3), 7.14 (s, 2 H, ArH), 7.60–7.91 (m, 4 H, ArH), 8.13
(d, 1 H, J=8.1 Hz, ArH), 9.28 (d, 1 H, J=8.1 Hz, ArH). 13
C
NMR (DMSO-d6) δ: 56.2, 56.2, 62.2, 65.1, 104.9, 104.9,
118.1, 120.2, 123.6, 129.7, 129.7, 131.1, 135.0, 137.0,
137.0, 146.1, 148.9, 154.9, 154.9, 157.1, 166.7. MS m/z
(%): 381.1 (M+1) (100), 383.1 (M+2) (20). Anal. Calcd.
For C21H17ClN2O3 (380.82): C, 66.23; H, 4.50; N, 7.36%.
Found: C, 66.27; H, 4.61; N, 7.40%.
5-Chloro-2-(4-nitrophenyl)benzo[h][1, 6]naphthyridine (8d)
Yellowish prism Yield: 0.055 g (68%),, mp. 207–209 °C; IR
(KBr): 3033, 3015, 1552, 1330 cm.-1; 1H NMR (DMSO-d6) δ:
7.65–7.74 (m, 4 H, ArH), 8.22 (d, 2 H, J=8.2 Hz, ArH), 8.38
(d, 1 H, J=8.7 Hz, ArH), 9.12 (d, 1 H, J=8.7 Hz, ArH), 9.28
(d, 2 H, J=8.2 Hz, ArH). 13C NMR (DMSO-d6) δ: 117.1,
119.9, 120.5, 121.4, 124.1, 124.1, 126.7, 126.7, 128.2, 129.7,
129.7, 133.0, 133.4, 137.2, 142.1, 145.1, 151.4, 191.2. MS m/
z (%): 336.15 (M+1) (100), 337.15 (M+2) (21). Anal. Calcd.
for C18H10ClN3O2 (335.74): C, 64.39; H, 3.00; N, 12.52%.
Found: C, 64.42; H, 2.98; N, 12.62%.
5-chloro-2-benzo[h][1, 6]naphthyridines (8a-d) Mixture of
4-amino-2-chloroquinoline-3-carbaldehyde 5 (0.050 g,
0.24 mmol), appropriate acetophenones 7a-d (0.24 mmol)
and ammonium acetate (1.20 mmol) was heated at 120 °C
for 20 min. (TLC monitoring, CH2Cl2/MeOH 10:0.5). The
mixture was then cooled to room temperature and stirred in
water (1.5 mL). The obtained solid was collected by suction
filtration. The crude compound was recrystallized from
absolute ethanol.
2,5-Diphenylbenzo[h][1, 6]naphthyridine (9a-h) A mixture
of 4-amino-2-aryl quinoline-3-carboxaldehyde 6a-c
(0.20 mmol) and appropriate acetophenones 7a-
h (0.20 mmol) in ammonium acetate (0.077 g, 1.0 mmol)
was heated at 120 °C for 20 min. (TLC monitoring,
CH2Cl2/MeOH 10:1). The reaction mixture was then cooled
to room temperature and poured in cold water (2.0 mL). The
precipitated solid was collected by suction filtration. dried
and recrystallized from ethanol to obtain solid.
5-Chloro-2-phenylbenzo[h][1, 6]naphthyridine (8a) Yield:
0.058 g (80%), off white crystals, mp. 179–181 °C; IR
(KBr): 3028, 3012, 1644, 1593 cm.-1; 1H NMR (DMSO-d6)
δ: 7.62–7.71 (m, 5 H, ArH), 8.20 (d, 1 H, J=8.2 Hz, ArH),
8.35 (d, 1 H, J=8.2 Hz, ArH), 8.42–8.51 (m, 4 H, ArH).
13C NMR (DMSO-d6) δ: 118.1, 119.8, 120.1, 122.4, 123.5,
123.5, 125.1, 125.1, 128.2, 129.7, 129.7, 132.1, 133.4,
137.2, 141.5, 145.1, 150.4, 155.8. MS m/z (%): 291.1 (M+
1) (100), 293.1 (M+2) (22). Anal. Calcd. for C18H11ClN2
(290.75): C, 74.36; H, 3.81, N, 9.63%. Found: C, 74.40; H,
3.75; N, 9.67%.
2, 5-Diphenylbenzo[h][1, 6]naphthyridine (9a) Yield:
0.055 g (82%), colorless crystals, mp. 129-132 °C; IR
(KBr): 3024, 3010, 1615 cm.-1; 1H NMR (DMSO-d6) δ: 7.58–
7.61 (m, 3 H, ArH), 7.62–7.67 (m, 3 H, ArH), 7.76–7.79 (m,
2 H, ArH), 7.89–7.94 (m 2 H, ArH), 8.15 (d, 1 H, J=8.1 Hz,
ArH), 8.41–8.46 (m, 4 H, ArH), 9.25 (d, 1 H, J=8.1 Hz,
ArH). 13C NMR (DMSO-d6) δ: 118.0, 119.8, 123.4, 124.2,
127.3, 127.5, 127.5, 128.4, 128.4, 129.0, 129.0, 129.0, 129.3,
129.7, 129.7, 130.4, 130.6, 137.1, 137.7, 138.2, 145.5, 148.1,
158.4, 159.8. MS m/z (%): 332.8 (M+) (100), 333.8 (M+1)
(20). Anal. Calcd. for C24H16N2 (332.4): C, 86.72; H, 4.85; N,
8.43%.Found: C,86.54; H, 4.70; N, 8.53%.
5-Chloro-2-(3,4-dimethoxyphenyl)benzo[h][1, 6]naphthyri-
dines (8b) Yield: 0.052 g (62%), colorless crystals, mp.
1
198–200 °C; IR (KBr): 3020, 3015, 1630, 1590 cm.-1; H
NMR (DMSO-d6) δ: 3.85 (s, 3 H, OCH3), 3.92 (s, 3 H,
OCH3), 7.12 (dd, 1 H, J=8.5 & 3.2 Hz, ArH), 7.85 (d, 1 H,
J=8.5 Hz, ArH), 7.87 (d, 1 H, J=7.6 Hz, ArH), 7.97 (d,
1 H, J=3.2 Hz, ArH), 8.25–8.30 (m, 4 H, ArH), 9.20 (d,
1 H, J=7.6 Hz, ArH). 13C NMR (DMSO-d6) δ: 55.4,
55.4, 111.5, 112.3, 117.6, 120.1, 123.9, 125.0, 127.0,
128.3, 129.7, 129.7, 130.5, 136.8, 138.5, 144.9, 148.1,
151.2, 158.5, 160.1. MS m/z (%): 351.1 (M+1) (100),
353.08 (M+2) (23). Anal. Calcd. for C20H15ClN2O2
(350.8): C, 68.48; H, 4.31; N, 7.99%. Found: C, 68.50;
H, 4.51; N, 8.01%.
2-(3,4-Dimehoxyphenyl)-5-phenylbenzo[h][1, 6]naphthyri-
dine (9b) Yield: 0.052 g (66%), colorless crystals, mp.
1
193–195 °C; IR (KBr): 3035, 3012, 1610 cm.-1; H NMR
(DMSO-d6) δ: 3.87 (s, 3 H, OCH3), 3.96 (s, 3 H, OCH3),
7.14 (dd, 1 H, J=8.4 & 2.9 Hz, ArH), 7.61–7.62 (m, 3 H,
ArH), 7.76–7.78 (m, 2 H, ArH), 7.81 (d, 1 H, J=8.4 Hz,
ArH), 7.88 (d, 1 H, J=2.9 Hz, ArH), 7.96 (d, 1 H, J=
8.4 Hz, ArH), 8.15 (d, 1 H, J=8.4 Hz, ArH), 8.27–8.37 (m,
4 H, ArH). 13C NMR (DMSO-d6) δ: 55.62, 55.62, 110.5,
5-Chloro-2-(2, 4, 6-trimethoxyphenyl)benzo[h][1, 6]naph-
thyridine (8c) Yield: 0.060 g (65%), colorless prism, mp.
1
215–218 °C; IR (KBr): 3032, 3010, 1632, 1601 cm.-1; H
NMR (DMSO-d6) δ: 3.81 (s, 3 H, OCH3), 3.99 (s, 6 H,

J Fluoresc (2011) 21:1617–1624
1623
111.7, 117.6, 119.3, 123.4, 124.2, 127.2, 128.3, 128.3, 129.0,
129.1, 129.7, 129.7, 130.3, 130.5, 136.6, 138.3, 145.6, 145.6,
149.1, 149.1, 151.1, 158.2, 159.7. MS m/z (%): 393.2 (M+1)
(100), Anal. Calcd. for C26H20N2O2 (392.45): C, 79.57; H,
5.14; N, 7.14%. Found: C, 79.39; H, 5.26; N, 7.29%.
3.89 (s, 3 H, OCH3), 3.97 (s, 6 H, OCH3), 7.16 (d, 2 H, J=
8.4 Hz, ArH), 7.73 (s, 2 H, ArH), 7.89 (d, 2 H, J=8.4 Hz,
ArH), 8.12 (d, 1 H, J=8.1 Hz, ArH), 8.36–8.47 (m, 4 H,
ArH), 9.21(d, 1 H, J=8.1 Hz, ArH). 13C NMR (DMSO-d6)
δ: 55.3, 56.1, 60.1, 105.1, 105.1, 113.8, 113.8, 117.9 119.8,
123.4, 124.0, 127.0, 129.0, 130.5, 130.6, 131.3, 131.3,
133.0, 136.9, 139.8, 145.7, 148.0, 153.3, 153.3, 158.0,
159.3, 160.0, 162.1. MS m/z (%): 453.2 (M+1) (100).
Anal. Calcd. for C28H24N2O4 (452.5): C, 74.32; H, 5.35; N,
6.19%. Found; C, 74.14; H, 5.26; N, 6.34%.
5-Phenyl-2-(2,4,6-trimethoxyphenyl) benzo[h][1, 6]naph-
thyridine (9c) Yield: 0.057 g (67%). coloerless crystals, mp.
1
228–230 °C; IR (KBr): 3033, 3018, 1620, 1210, cm.-1; H
NMR (DMSO-d6) δ: 3.78 (s, 3 H, OCH3), 3.97 (s, 6 H,
OCH3), 7.62–7.63 (m, 3 H, ArH), 7.73 (s, 2 H, ArH), 7.77–
7.85 (m, 4 H, ArH), 7.89 (s, 2 H, ArH), 8.15 (d, 1 H, J=
8.1 Hz, ArH), 9.25 (d, 1 H, J=8.1 Hz, ArH). 13C NMR
(DMSO-d6) δ: 56.0, 56.0, 60.2, 64.9, 105.1, 105.1, 117.9,
119.9, 123.6, 124.2, 128.4, 129.1, 129.1, 129.2, 129.7, 129.7,
130.6, 133.2, 136.9, 136.9, 145.7, 148.1, 153.3, 153.3, 153.3,
158.4, 165.6. MS m/z (%): 423.2 (M+1) (99), 424.2 (M+2)
(22). Anal. Calcd. for C27H22N2O3 (422.48): C, 76.76; H,
5.25; N, 6.63%. Found: C, 76.51; H, 5.30; N, 6.44%.
2-(3,4-Dimethoxyphenyl)-5-(4-nitrophenyl)benzo[h][1, 6]
naphthyridine (9 g) Yield: 0.055 g (74%), reddish crystals,
mp. 222–225 °C; IR (KBr): 3132, 3040, 1610, 1540,
1
1310 cm.-1; H NMR (DMSO-d6) δ: 3.85 (s, 3 H, OCH3),
3.92 (s, 3 H, OCH3), 7.19 (dd, J=9.1 & 2.8 Hz, ArH), 7.42
(d, 1 H, J=9.1 Hz, ArH), 7.62 (d, 1 H, J=2.8 Hz, ArH),
7.72 (d, 2 H, J=8.2 Hz, ArH), 7.80–8.10 (m, 4 H, ArH),
8.16 (d, 1 H, J=8.5 Hz, ArH), 8.32 (d, 2 H, J=8.2 Hz,
ArH), 9.25 (d, 1 H, J=8.5 Hz, ArH). 13C NMR (DMSO-d6)
δ: 56.1, 56.1, 111.0, 111.5, 118.1, 119.7, 124.0, 124.5,
127.9, 128.5, 128.9, 129.1, 129.6, 129.9, 130.7, 131.2,
136.5, 136.5, 139.2, 146.0, 146.0, 149.2, 149.2, 151.2,
159.1, 190.2. MS m/z (%): 438.5 (M+1) (99). Anal. Calcd.
For C26H19N3O4 (437.45): C, 71.39; H, 4.38; N, 9.61%.
Found: C, 71.35; H, 4.40; N, 9.55%.
5-(4-Methoxyphenyl)-2-phenylbenzo[h][1, 6]naphthyridine
(9d) Yield: 0.046 g (68%), colorless crystals, mp. 197–
199 °C; IR (KBr): 3041, 3021, 1607, 1251 cm.-1; 1H NMR
(DMSO-d6) δ: 4.00 (s, 3 H, OCH3), 7.12–7.24 (m, 5 H,
ArH), 7.26 (d, 2 H, J=8.2 Hz, ArH), 7.71–7.94 (m, 4 H,
ArH), 8.01 (d, 2 H, J=8.2 Hz, ArH), 8.44 (d, 1 H, J=
9.0 Hz, ArH), 8.75 (d, 1 H, J=9. 0 Hz, ArH). 13C NMR
(DMSO-d6) δ: 55.2, 118.0, 119.8, 123.4, 124.2, 127.3,
127.5, 127.5, 128.4, 128.4, 129.0, 129.0, 129.0, 129.2,
129.7, 129.7, 130.4, 130.6, 137.1, 137.7, 138.2, 145.5,
148.1, 158.4, 159.8. MS m/z (%): 363.15 (M+1) (100).
Anal. Calcd. for C25H18N2O (362.4): C, 82.85; H, 5.01; N,
7.73%. Found; C, 83.01; H, 5.09; N, 7.81%.
2-(2,4,6-Trimethoxyphenyl)-5-(4-nitrophenyl)benzo[h][1, 6]
naphthyridine (9 h) Yield: 0.058 g (73%), off white crystals,
1
mp. 186–189 °C; IR (KBr): 3033, 3014, 1615 cm.-1; H
NMR (DMSO-d6) δ: 3.80 (s, 3 H, OCH3), 3.92 (s, 6 H,
OCH3), 7.16 (d, 2 H, J=9.0 Hz, ArH), 7.72–7.80 (m, 4 H,
ArH), 7.85 (d, 1 H, J=8.0 Hz, ArH), 8.15 (d, 2 H, J=
9.0 Hz, ArH), 8.32 (s, 2 H, ArH), 9.22 (d, 1 H, J=8.0 Hz,
ArH). 13C NMR (DMSO-d6) δ: 56.10, 56.10, 60.2, 106.1,
106.1, 114.0, 114.0, 118.0, 119.1, 123.5, 124.0, 127.1,
129.2, 131.1, 131.5, 131.7, 131.7, 133.5, 137.1, 140.1,
145.9, 149.0, 154.1, 158.5, 159.5, 191.0. MS m/z (%):
468.15 (M+1) (100). Anal. Calcd. For C27H21N3O5
(467.47): C, 69.37; H, 4.53; N, 8.99%. Found: C, 69.40;
H, 4.56; N, 9.05%.
2-(3,4-Dimethoxyphenyl)-5-(4-methoxyphenyl)benzo[h][1,
6]naphthyridine (9e) Yield: 0.051 g (67%), colorless
crystals, mp. 193–195 °C; IR (KBr): 3034, 3012,
1
1605 cm.-1; H NMR (DMSO-d6) δ: 3.87-3.88 (s, 6 H,
OCH3), 3.96 (s, 3 H, OCH3),7.29(d, 2 H, J=8.2 Hz, ArH),
7.34 (dd, 1 H, J=8.6 & 2.8 Hz, ArH), 7.64 (d, 1 H, J=
8.6 Hz, ArH), 7.79–7.98 (m, 4 H, ArH), 8.11 (d, 1 H, J=
2.8 Hz, ArH), 8.14 (d, 2 H, J=8.2 Hz, ArH). 13C NMR
(DMSO-d6) δ: 55.3, 55.6, 55.6, 110.5, 111.7, 117.6, 119.3,
123.4, 124.2, 127.2, 128.3, 128.3, 129.0, 129.1, 129.7,
130.3, 130.5, 136.6, 136.6, 138.3, 145.6, 145.6, 149.1,
149.1, 151.1, 158.2, 159.7. MS m/z (%): 423.1 (M+1) (99),
Anal. Calcd. for C27H22N2O3 (422.48): C, 76.76; H, 5.25;
N, 6.63%. Found: C, 76.89; H, 5.41; N, 6.82%.
Acknowledgement The authors thank UGC and CSIR New Delhi
for financial assistance, Dept. of Chemistry, University of Pune, and
Principal, K. T. H. M. College, Nashik—422 002 for facilities.
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