An expedient four-component domino protocol for the synthesis of novel benzo[a]phenazine annulated heterocycles and their photophysical studies

Article abstract of DOI:10.1039/c2gc35644a

A new one pot two-step domino protocol for the efficient synthesis of novel fluorescent benzo[a]phenazine fused derivatives has been developed. The synthesis was achieved by reacting 2-hydroxynaphthalene-1,4-dione, ortho-phenylenediamines, aromatic aldehydes and cyclic 1,3-dicarbonyl compounds in the presence of a catalytic amount of p-TSA in PEG-400 at 70 °C. The structural assignment has been unambiguously confirmed by X-ray analysis. The present finding provides an efficient and promising synthetic strategy for the synthesis of libraries with functional group diversity.

Full text of DOI:10.1039/c2gc35644a

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PAPER
An expedient four-component domino protocol for the synthesis of novel
benzo[a]phenazine annulated heterocycles and their photophysical studies†
Jitender M. Khurana,* Ankita Chaudhary, Anshika Lumb and Bhaskara Nand
Received 27th April 2012, Accepted 28th May 2012
DOI: 10.1039/c2gc35644a
A new one pot two-step domino protocol for the efficient synthesis of novel fluorescent benzo[a]-
phenazine fused derivatives has been developed. The synthesis was achieved by reacting
2-hydroxynaphthalene-1,4-dione, ortho-phenylenediamines, aromatic aldehydes and cyclic 1,3-dicarbonyl
compounds in the presence of a catalytic amount of p-TSA in PEG-400 at 70 °C. The structural
assignment has been unambiguously confirmed by X-ray analysis. The present finding provides an
efficient and promising synthetic strategy for the synthesis of libraries with functional group diversity.
This incited us to develop synthetic methodology for novel
benzo[a]phenazine derivatives and to study the optical behaviour
Introduction
Phenazine based compounds are the some of the most abundant
natural products, having a myriad of biological functions such as
antimalarial, trypanocidal, fungicidal, antiplatelete and antituber-
culosis activities.1 Fluorescent phenazine derivatives are also
used as photo-sensitizers in photodynamic therapy (PDT)2
wherein the combination of light and photo-sensitizer generates
highly reactive oxygen species or hydroxyl radicals near the
tumor to selectively destroy the targeted tissue.
Multi-component domino/sequential reactions are character-
ized by elegance and convergence resulting in rapid synthesis of
molecules with diversified structures with good yields and selec-
tivity.3 These reactions obviate the need for isolation and purifi-
cation of the intermediates, resulting in maximization of yield
and reduction of waste, rendering the protocols ecofriendly.4 The
development of novel synthetic routes for the synthesis of privi-
leged heterocyclic scaffolds of medicinal relevance, which
combine the benefits of multi-component protocols with the
environmental benefits of using non-toxic reagents and green
solvents, remains a continuing challenge at the forefront of
modern chemistry.
Replacement of hazardous solvents with environmentally
benign solvents5 is one of the major focus areas of green chemi-
stry. We have been engaged in the development of novel green
methodologies for the synthesis of variety of heterocycles using
green reaction media.6 The environmentally benign nature of
PEG and the versatility of p-TSA7 encouraged us to couple them
together and study their utility in the synthesis of novel phena-
zine derivatives. Moreover, a considerable amount of research
has been focused on the photophysical properties of phenazines.8
of these derivatives by UV-vis and fluorescence spectroscopy.
Results and discussion
This is the first report on the convergent four-component domino
protocol for the synthesis of novel benzo[a]phenazines from
2-hydroxynaphthalene-1,4-dione, ortho-phenylene diamines,
aromatic aldehydes and cyclic-1,3-dicarbonyl compounds in
PEG-400 at 70 °C using p-TSA as catalyst.
The model reactions of 2-hydroxynaphthalene-1,4-dione
(1.0 mmol), o-phenylenediamine (1.0 mmol), 4-chlorobenz-
aldehyde, and cyclohexane-1,3-dione (I) (1.0 mmol) were
attempted in various solvents such as ethylene glycol, PEG-200,
PEG-400, PEG-600, ethanol, water, and acetonitrile using
p-TSA as a catalyst. When this four-component condensation
reaction was attempted in ethylene glycol at 70 °C using p-TSA
(10 mol%) as catalyst, it was observed that the reaction was com-
plete after 6 h, but yielded a mixture of products, which were
separated by column chromatography. One of the products was
identified to be the novel compound, 16-(4-chlorophenyl)-
2,3,4,16-tetrahydro-1H-benzo[a]chromeno[2,3-c]phenazin-1-one
(2a) by spectroscopic analysis (entry 1, Table 1). The yield of
the product 2a however, was only 20%. After further manipu-
lation of the reaction conditions, we observed that if the reaction
was performed by initial condensation of 2-hydroxynaphthalene-
1,4-dione (1.0 mmol) and o-phenylenediamine (1.0 mmol) in
ethylene glycol at 70 °C using p-TSA (10 mol%) as catalyst to
form the intermediate benzo[a]phenazin-5-ol (1)9 in 30 min,
followed by the addition of 4-chlorobenzaldehyde (1.0 mmol)
and cyclohexane-1,3-dione (1.0 mmol) in the same pot, the reac-
tion was found to be complete after 3.5 h and afforded 60% of
2a after work up (entry 2, Table 1). The reactions attempted in
PEG-200, PEG-400 and PEG-600 in an analogous manner
resulted in the formation of the desired phenazine derivative 2a
in 73, 92 and 90% yield, respectively (entries 3–5, Table 1).
Department of Chemistry, University of Delhi, Delhi-110007, India.
E-mail: jmkhurana@chemistry.du.ac.in; Fax: +91 11 27666605;
Tel: +91 11 27667725-1384
†CCDC 878459. For crystallographic data in CIF or other electronic
format see DOI: 10.1039/c2gc35644a
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Table 1 Optimisation of reaction conditions for the synthesis of
16-(4-chlorophenyl)2,3,4,16-tetrahydro-1H-benzo[a]chromeno[2,3-c]
phenazin-1-one (2a)
Temp. Time Yield
Entry Solvent
Catalyst Mol% (°C)
(h)
(%)
1
2
3
4
5
6
7
8
Ethylene glycol p-TSA
Ethylene glycol p-TSA
10
10
10
10
10
10
10
10
5
20
10
10
10
10
70
70
70
70
70
78
100
80
70
70
70
70
90
100
6
4
3
2
2
4
6
6
4
2
4
6
2
2
20a,b
60c
PEG-200
PEG-400
PEG-600
EtOH
p-TSA
p-TSA
p-TSA
p-TSA
p-TSA
p-TSA
p-TSA
p-TSA
H2SO4
HCl
73c
92c
90c
70c
50c,d
30c,d
70c
Scheme 1 Synthesis of benzo[a]phenazines.
H2O
CH3CN
PEG-400
PEG-400
PEG-400
PEG-400
PEG-400
PEG-400
9
10
11
12
13
14
92c
cyclohexane-1,3-dione (I) and 5,5-dimethylcyclohexane-
1,3-dione (II) were attempted under the optimized four-com-
ponent domino methodology outlined above. All the reactions
were complete in 2–2.5 h and resulted in the formation of the
corresponding novel benzo[a]chromeno-phenazinone derivatives
(Scheme 1, entries 1–14, Table 2) in high yields as identified by
spectral data.
Replacement of cyclohexane-1,3-dione (I) with cyclopentane-
1,3-dione (III), under otherwise identical reaction conditions
afforded a novel series of benzo[a]cyclopenta-pyrano[2,3-c]-
phenazines (Scheme 1, entries 15–17, Table 2) in high yields.
All products are yellow coloured and show maximum wave-
lengths ranging from 412 to 430 nm.
78c
30c,d
92c
p-TSA
p-TSA
91c
a 2-Hydroxynaphthalene-1,4-dione (1.0 mmol), o-phenylenediamine,
4-chlorobenzaldehyde (1a), cyclohexane-1,3-dione and p-TSA
(0.1 mmol) were added simultaneously. b Mixture of products.
c 2-Hydroxynaphthalene-1,4-dione (1.0 mmol), o-phenylenediamine and
p-TSA were first allowed to stir in solvent at appropriate temp. for
30 min, followed by addition of 4-chlorobenzaldehyde (1a),
cyclohexane-1,3-dione. d Incomplete reaction.
This sequential four component condensation of aromatic
aldehydes, 2-hydroxy-1,4-naphthoquinone, 1,3-cyclic dicarbonyl
compounds and 4,5-dichlorobenzene-1,2-diamine also afforded
the corresponding benzo[a]chromeno-phenazinone derivatives in
high yields (Table 2, entries 18–20). Structural assignments have
The reaction performed using p-TSA (10 mol%) as catalyst in
ethanol under reflux conditions was complete in 6 h and gave
70% of 2a (entry 6, Table 1), whereas the reactions conducted
under reflux in water and acetonitrile were observed to be incom-
plete even after 6 h, and yielded 50 and 30% of 2a, respectively
(entries 7–8, Table 1). It can be inferred from Table 1, that
PEG-400 is the most suitable reaction medium for the above
transformation.
1
been made on the basis of IR, H NMR, 13C NMR and mass
spectra. Additionally, the structures of the synthesized novel
benzo[a]chromeno-phenazinone derivatives (2) have been
confirmed by the single crystal X-ray diffraction analysis of com-
pound 2e (Fig. 1).†
We have also examined the recyclability of the reaction media
i.e. polyethylene glycol (PEG-400), during the synthesis of 2a.
Upon completion, the reaction was quenched with water and the
solid product was collected by filtration. The filtrate containing
polyethylene glycol was rinsed with ether and further vacuumed
to dryness at 90 °C for 2 h to remove any trapped water, to
afford PEG-400 which was reused directly for the next run. Mar-
ginal loss in the yield of the products was observed in the first
three runs (92, 90, and 87%, respectively).
A speculative mechanistic explanation for this reaction is pro-
vided in Scheme 2. The formation of 2 proceeds via initial con-
densation of 2-hydroxynaphthalene-1,4-dione and diamine to
afford benzo[a]phenazin-5-ol (1) as reported which in situ gene-
rates an ortho-quinone methide (o-QM) intermediate upon
nucleophilic addition to aldehyde. Subsequent Michael addition
of the o-QM with a cyclic 1,3-dicarbonyl compound, followed
by cyclization and dehydration leads to the formation of 2.
The effect of the amount of the catalyst on the reaction time or
yield of the product in the above reaction was also examined.
It was observed that the reaction using 5 mol% of the catalyst
required a longer time (4 h) (entry 9, Table 1) and afforded 70%
of the desired product, while no significant improvement in the
time of completion or yield of the product was observed in
the reaction attempted using a higher molar concentration of the
catalyst p-TSA (20 mol%) (entry 10, Table 1). We have also
attempted the reaction using other acid catalysts under otherwise
identical conditions. The reaction performed using H2SO4 as
catalyst in PEG-400 at 70 °C underwent completion in 4 h,
yielding 78% of 2a (entry 11, Table 1), while the reaction using
HCl as catalyst did not proceed to completion and yielded only
30% of 2a after 6 h (entry 12, Table 1). Moreover, no substantial
effect on the yield and reaction time was observed on conducting
the reactions in PEG-400 at 90 and 100 °C using p-TSA as
catalyst (entries 13–14, Table 1). Therefore, a one pot domino
reaction of equimolar amounts of aldehyde, 2-hydroxynaphtha-
lene-1,4-dione, o-phenylenediamine and cyclohexane-1,3-dione
using 10 mol% of p-TSA as catalyst in PEG-400 at 70 °C
proved to be the optimum conditions.
Photophysical studies
Subsequently, reactions of other diversely substituted aromatic
aldehydes bearing electron donating or electron-withdrawing
functional groups, 2-hydroxynaphthalene-1,4-dione, o-phenylene
diamine and cyclic 1,3-dicarbonyl compounds such as
The spectral characteristics of the compounds such as absorption
maxima (λmax), emission maxima (λem) and molar extinction
coefficient (ε) were measured in chloroform and are presented in
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Table 2 Synthesis of benzo[a]phenazine fused derivatives (2a–t) using p-TSA as catalyst in PEG-400 at 70 °C
Entry
Product
Ar group
Cyclic-1,3-dicarbonyl compound
R group
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
2a
2b
2c
2d
2e
2f
2g
2h
2i
4-ClC6H4
4-CH3C6H4
3-BrC6H4
4-CH3OC6H4
3,4,5-(CH3O)3C6H2
4-ClC6H4
4-CH3C6H4
4-BrC6H4
I
I
I
I
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Cl
Cl
Cl
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2.5
2.5
2.5
2.5
2.5
2.5
92
87
91
88
89
90
88
89
90
82
83
89
87
89
88
86
84
88
87
89
I
II
II
II
II
II
II
II
II
II
III
III
III
II
II
I
9
3-ClC6H4
10
11
12
13
14
15
16
17
18
19
20
2j
2k
2l
2-Naphthyl
4-Me2CHC6H4
4-(OH),3-(CH3O)C6H3
Thien-2-yl
4-CH3OC6H4
4-CH3C6H4
4-CH3OC6H4
3-ClC6H4
2m
2n
2o
2p
2q
2r
2s
2t
4-ClC6H4
4-CH3C6H4
4-ClC6H4
Scheme 2 Proposed reaction pathway for synthesis of 2.
Table 3 Photophysical data of compound 2 in chloroform
Fig. 1 X-Ray crystallographic structure of 2e.
Product
λmax (nm)
ε × 105 (L mol−1 cm−1
)
λem (nm)
Table 3. Figs. 2 and 3show the absorption and fluorescence
spectra of all the products, respectively.
2a
2b
2c
2d
2e
2f
2g
2h
2i
371, 393, 415
374, 395, 416
372, 393, 415
373, 395, 416
371, 394, 415
372, 393, 415
373, 395, 416
372, 393, 415
372, 393, 415
374, 395, 416
373, 396, 416
371, 393, 415
373, 395, 416
370, 390, 412
370, 390, 412
372, 391, 412
383, 405, 428
385, 407, 430
383, 405, 428
0.12, 0.18, 0.19
0.08, 0.12, 0.12
0.09, 0.12, 0.14
0.10, 0.07, 0.10
0.06, 0.08, 0.08
0.10, 0.14, 0.16
0.10, 0.14, 0.15
0.10, 0.15, 0.16
0.12, 0.17, 0.18
0.10, 0.13, 0.13
0.08, 0.10, 0.11
0.13, 0.19, 0.21
0.08, 0.11, 0.11
0.06, 0.08, 0.09
0.11, 0.15, 0.16
0.09, 0.12, 0.16
0.06, 0.10, 0.11
0.09, 0.13, 0.15
0.07, 0.11, 0.12
447
452
452
451
444
447
453
449
445
465
457
459
454
449
449
448
457
459
457
All the compounds, except 2k which was not soluble in
CHCl3, showed strong absorptions, with maximum wavelengths
ranging from 412 to 430 nm. All the products displayed three
absorption maxima, band I in the region of 370–380 nm, band II
in the region of 390–407 nm and band III in the region of
415–430 nm. The increase in conjugation and increased electron
density associated with chlorine groups in 4,5-dichlorobenzene-
1,2-diamine led to a large bathochromic shift of the absorption
maxima in compounds 2r, 2s and 2t.
From Fig. 3, it can be inferred that the products are fluorescent
in solution. All of the compounds displayed almost similar fluor-
escence spectra in the range of 444–465 nm. A fluorescence
excitation wavelength (λext) of 370 nm was used for all the com-
pounds. Since the electronic and steric effects of the substituted
groups on the aromatic aldehyde have little influence on the flu-
orescence properties, it can be inferred that the luminescence of
the products is a direct result of their framework.
2j
2l
2m
2n
2o
2p
2q
2r
2s
2t
chloroform, dichloromethane, dimethylsulphoxide and aceto-
nitrile were screened (It was not possible to measure the absorp-
tion and fluorescence of 2a in non-polar solvents such as hexane
To investigate the influence of solvents on the fluorescence
spectra of compounds 2a–t, different solvents such as
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Fig. 4 Lippert–Mataga plots for 2a.
Fig. 2 UV-vis spectra of compounds 2a–t in chloroform solution
(5 × 10−5 M).
Conclusions
In conclusion, the present work describes a new one-pot, conver-
gent, expedient sequential protocol for the synthesis of benzo[a]-
phenazine fused derivatives via the reaction of 2-hydroxy-
naphthalene-1,4-dione, ortho-phenylenediamines,
aromatic
aldehydes and cyclic-1,3-dicarbonyl compounds in the presence
of p-TSA in polyethylene glycol (PEG-400) at 70 °C in high to
excellent yields. The protocol is environmentally benign, has a
high atom-economy and offers recyclability of the reaction
media i.e. PEG-400. The benzo[a]phenazine derivatives syn-
thesized are of great interest for their fluorescent properties and
potential biological activity.
Experimental
All the chemicals were commercial and were purchased from
Sigma-Aldrich or Merck and were used as received. Thin layer
chromatography (GF254) was used to monitor reaction progress.
Melting points were determined on a melting point apparatus
and are uncorrected. IR (KBr) spectra were recorded on a
Perkin-Elmer FTIR spectrophotometer and the values are
expressed as νmax cm−1. Mass spectral data were recorded on
JEOL-AccuTOF JMS-T100 mass spectrometer having a DART
Fig. 3 Fluorescence spectra of compounds 2a–t in chloroform solution
(5 × 10−5 M).
Table 4 Spectral properties of compound 2a in different solvents
ε × 104
Stokes
λmax
(nm)
(Lmol−1
λem
shift (Δν)
1
source. The H NMR and 13C NMR spectra were recorded on
Entry Solvent
cm−1
)
(nm) cm−1
Jeol JNM ECX-400P at 400 and 100 MHz respectively, using
TMS as an internal standard. The chemical shift values are
recorded on δ scale and the coupling constants (J) are in Hz.
UV-vis absorption spectra were recorded on an Analytikjena
Specord 250 spectrophotometer. The fluorescence spectra were
measured at Cary Eclipse fluorescence spectrophotometer.
X-Ray intensity data were collected on an Oxford Diffraction
Xcalibur CCD diffractometer with graphite monochromated
Mo Kα radiation (λ = 0.71073 Å) at 298 K.
1
2
3
4
Chloroform
Dimethylsulphoxide 418
Dichloromethane
Acetonitrile
415
0.16
0.14
0.08
0.05
447
461
443
460
1725
2231
2066
2473
415
413
and toluene due to poor solubility of compounds 2a–t in such
solvents) (Table 4). The fluorescence spectra shift significantly
to the red upon increasing solvent polarity. The Lippert–Mataga
plot10 of the Stokes shift (Δν) as a function of orientation polar-
izability (Δf) shows a good linear relationship, suggesting that
specific solute–solvent interactions are involved, which is known
to consist of several effects i.e., dipole–dipole interactions and
dipole induced dipole interactions. Relative contribution of indi-
vidual effects depends on the type of solvent used (Fig. 4).
General procedure for the synthesis of benzo[a]phenazine
derivatives (2a–2t)
A mixture of 2-hydroxynaphthalene-1,4-dione (1.0 mmol),
o-phenylenediamine/4,5-dichlorobenzene-1,2-diamine (1.0 mmol),
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16-(4-Methoxyphenyl)-2,3,4,16-tetrahydro-1H-benzo[a]chromeno-
[2,3-c]phenazin-1-one (2d). 1H NMR (400 MHz, CDCl3) δ =
9.33–9.31 (m, 1H, ArH), 8.36 (d, J = 7.3 Hz, 1H, ArH),
8.24–8.21 (m, 2H, ArH), 7.82–7.75 (m, 4H, ArH), 7.50 (d, J =
8.8 Hz, 2H, ArH), 6.68 (d, J = 8.8Hz, 2H, ArH), 6.09 (s, 1H,
CH), 3.62 (s, 3H, OCH3), 3.00–2.93 (m, 1H, CH2), 2.88–2.80
(m, 1H, CH2), 2.55–2.41 (m, 2H, CH2), 2.20–2.10 (m, 2H,
CH2); 13C NMR (100 MHz, CDCl3): δ = 197.11, 165.07,
157.82, 146.77, 142.53, 141.87, 140.84, 137.43, 130.79, 129.89,
129.82, 129.76, 129.44, 129.40, 129.33, 128.23, 126.50, 125.40,
121.86, 116.52, 113.24, 55.00, 37.15, 32.59, 27.54, 20.55;
IR (νmax cm−1) (KBr): 2926, 2836, 1655, 1370, 1207, 1029;
MS (ESI) m/z calcd for C30H22N2O3: 458.16, found: 459.23
[M+ + H].
p-TSA (10 mol% or 0.1 mmol) and 5 ml of PEG-400 was
placed in a 50 mL round-bottomed flask and the contents were
stirred magnetically in an oil-bath maintained at 70 °C until an
orange solid was formed (30 min). Aldehyde (1.0 mmol) and
cyclohexane-1,3-dione/dimedone/cyclopentane-1,3-dione
(1.0 mmol) were then added to the above reaction mixture which
was heated further for an appropriate time as shown in Table 2.
The progress of the reaction was monitored by TLC (eluent:
methanol–chloroform, 10 : 90 v/v). After completion of the reac-
tion, the reaction mixture was allowed to cool at room tempera-
ture and was quenched with water (∼5 mL). The precipitate
formed was collected by filtration at pump and washed with
water. The crude product so obtained, was purified by column
chromatography over silica gel (100–200 mesh) to afford pure 2.
The products were characterized by IR, UV, 1H NMR, 13C NMR
and Mass spectra.
16-(3,4,5-Trimethoxyphenyl)-2,3,4,16-tetrahydro-1H-benzo[a]-
chromeno[2,3-c]phenazin-1-one (2e). 1H NMR (400 MHz,
CDCl3) δ = 9.33–9.31 (m, 1H, ArH), 8.35–8.32 (m, 1H, ArH),
8.24–8.21(m, 1H, ArH), 8.19–8.16 (m, 1H, ArH), 7.81–7.73 (m,
4H, ArH), 6.81 (s, 2H, ArH), 6.10 (s, 1H, CH), 3.72 (s, 6H,
OCH3), 3.72 (s, 3H, OCH3), 2.99–2.93 (m, 1H, CH2), 2.86–2.80
(m, 1H, CH2), 2.55–2.93 (m, 2H, CH2), 2.16–2.10 (m, 2H,
CH2); 13C NMR (100 MHz, CDCl3): δ = 197.05, 165.62,
152.62, 146.77, 142.40, 141.93, 140.89, 140.48, 130.82, 130.00,
129.90, 129.55, 129.06, 128.41, 126.48, 125.50, 121.94, 116.14,
106.31, 60.61, 56.10, 37.20, 33.36, 29.67, 27.62, 20.66;
IR (νmax cm−1) (KBr): 3433, 2932, 1653, 1374, 1205; MS (ESI)
m/z calcd for C32H26N2O5: 518.18, found: 519.18 [M+ + H].
16-(4-Chlorophenyl)-2,3,4,16-tetrahydro-1H-benzo[a]chromeno-
[2,3-c]phenazin-1-one (2a). 1H NMR (400 MHz, CDCl3) δ =
9.34–9.32 (m, 1H, ArH), 8.37–8.35 (m, 1H, ArH), 8.24–8.18
(m, 2H, ArH), 7.85–7.75 (m, 4H, ArH), 7.51 (d, J = 8.0 Hz, 2H,
ArH), 7.10 (d, J = 8.0 Hz, 2H, ArH), 6.09 (s, 1H, CH),
3.00–2.93 (m, 1H, CH2), 2.88–2.80 (m, 1H, CH2), 2.54–2.41
(m, 2H, CH2), 2.2–2.09 (m, 2H, CH2); 13C NMR (100 MHz,
CDCl3): δ = 196.97, 165.28, 146.91, 143.67, 142.47, 141.63,
140.91, 140.77, 131.83, 130.92, 130.39, 129.91, 129.55, 129.40,
129.32, 128.47, 127.98, 126.33, 125.46, 121.94, 116.00, 115.71,
37.09, 33.15, 27.55, 20.50; IR (νmax cm−1) (KBr): 2922, 1653,
1364, 1206; MS (ESI) m/z calcd for C29H19ClN2O2: 462.11,
found: 463.19 [M+ + H], 465.19 [M+ + H + 2].
16-(4-Chlorophenyl)-3,3-dimethyl-2,3,4,16-tetrahydro-1H-benzo-
[a]chromeno[2,3-c]phenazin-1-one (2f). 1H NMR (400 MHz,
CDCl3) δ = 9.43–9.32 (m, 1H, ArH), 8.36–8.34 (m, 1H, ArH),
8.24–8.10 (m, 2H, ArH), 7.85–7.75 (m, 4H, ArH), 7.52 (d, J =
8.7 Hz, 2H, ArH), 7.11 (d, J = 8.8 Hz, 2H, ArH), 6.07(s, 1H,
CH), 2.82 and 2.72 (AB system, J = 16.8 Hz, 2H, CHaCHbC-
(CH3)2), 2.40 and 2.29 (AB system, J = 16.1 Hz, 2H,
CHaCHbCO), 1.19 (s, 3H, CH3), 1.10 (s, 3H, CH3); 13C NMR
(100 MHz, CDCl3): δ = 196.80, 163.64, 146.87, 143.49, 142.43,
141.60, 140.88, 140.72, 131.80, 130.88, 130.38, 129.91, 129.86,
129.52, 129.38, 129.27, 128.43, 127.94, 126.31, 125.43, 121.91,
115.67, 114.66, 50.88, 41.21, 33.20, 32.42, 29.45, 27.33;
IR (νmax cm−1) (KBr): 3055, 2924, 1661, 1371, 1206; MS (ESI)
m/z calcd C31H23ClN2O2: 490.14, found: 491.22 [M+ + H],
493.22[M+ + H + 2].
16-(4-Methylphenyl)-2,3,4,16-tetrahydro-1H-benzo[a]chromeno-
[2,3-c]phenazin-1-one (2b). 1H NMR (400 MHz, CDCl3) δ =
9.34–9.32 (m, 1H, ArH), 8.38 (d, J = 7.3 Hz, 1H, ArH),
8.24–8.22 (m, 2H, ArH), 7.84–7.74 (m, 4H, ArH), 7.48 (d, J =
8.0 Hz, 2H, ArH), 6.95 (d, J = 7.3 Hz, 2H, ArH), 6.13 (s, 1H,
CH), 3.00–2.94 (m, 1H, CH2), 2.88–2.80 (m, 1H, CH2),
2.55–2.41 (m, 2H, CH2), 3.00–2.94 (m, 1H, CH2), 2.20–2.09
(m, 2H, CH2), 2.14 (s, 3H, CH3); 13C NMR (100 MHz, CDCl3):
δ = 196.98, 165.10, 146.82, 142.55, 142.20, 141.88, 140.88,
135.69, 130.80, 129.81, 129.74, 129.38, 129.33, 128.84, 128.61,
128.24, 126.50, 125.42, 121.88, 116.53, 116.48, 37.16, 33.05,
27.56, 20.97, 20.53; IR (νmax cm−1) (KBr): 2954, 1656, 1372,
1209; MS (ESI) m/z calcd for C30H22N2O2: 442.17, found:
443.16[M+ + H].
3,3-Dimethyl-16-(4-methylphenyl)-2,3,4,16-tetrahydro-1H-
benzo[a]chromeno[2,3-c]phenazin-1-one (2g). 1H NMR (400 MHz,
CDCl3) δ = 9.35–9.33 (m, 1H, ArH), 8.38–8.36 (m, 1H, ArH),
8.25–8.22 (m, 2H, ArH), 7.85–7.74 (m, 4H, ArH), 7.49 (d,
J = 8.0 Hz, 2H, ArH), 6.99 (d, J = 8.0 Hz, 2H, ArH), 6.10 (s,
1H, CH), 2.83 and 2.72 (AB system, J = 17.6 Hz, 2H,
CHaCHbC(CH3)2), 2.39 and 2.29 (AB system, J = 16.1 Hz, 2H,
CHaCHbCO), 2.1 (s, 1H, CH3), 1.18 (s, 3H, CH3), 1.12 (s, 3H,
CH3); 13C NMR (100 MHz, CDCl3): δ = 196.91, 163.52,
146.85, 142.67, 141.98, 140.85, 135.67, 130.87, 129.81, 129.77,
129.45, 129.40, 129.34, 128.86, 128.59, 128.25, 126.59, 125.44,
121.91, 116.65, 115.22, 50.98, 41.28, 33.14, 32.46, 29.43,
27.49, 20.97; IR (νmax cm−1) (KBr): 2928, 1601, 1367, 1206;
MS (ESI) m/z calcd for C32H26N2O2: 470.19, found: 471.27
[M+ + H].
16-(3-Bromophenyl)-2,3,4,16-tetrahydro-1H-benzo[a]chromeno-
[2,3-c]phenazin-1-one (2c). 1H NMR (400 MHz, CDCl3) δ =
9.34–9.32 (m, 1H, ArH), 8.40–8.36 (m, 2H, ArH), 8.22–8.20
(m, 1H, ArH), 7.86–7.73 (m, 4H, ArH), 7.45–7.41 (m, 2H,
ArH), 7.06–7.02 (m, 1H, ArH), 6.86–6.82 (m, 1H, ArH),
6.28 (s, 1H, CH), 2.99–2.92 (m, 1H, CH2), 2.89–2.81 (m, 1H,
CH2), 2.48–2.45 (m, 2H, CH2), 2.10–2.08 (m, 2H, CH2);
13C NMR (100 MHz, CDCl3): δ = 196.82, 164.91, 146.96,
143.96, 142.66, 141.94, 140.82, 133.14, 132.14, 131.07, 129.88,
129.77, 129.48, 129.24, 128.51, 127.55, 126.80, 125.38, 122.08,
37.19, 35.00, 27.67, 20.46; IR (νmax cm−1) (KBr): 2928, 1655,
1367, 1210; MS (ESI) m/z calcd for C29H19BrN2O2: 506.06,
found: 507.14[M+ + H], 509.15 [M+ + H + 2].
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16-(4-Bromophenyl)-3,3-dimethyl-2,3,4,16-tetrahydro-1H-
benzo[a]chromeno[2,3-c]phenazin-1-one (2h). 1H NMR (400 MHz,
CDCl3) δ = 9.36–9.34 (m, 1H, ArH), 8.38–8.35 (m, 1H, ArH),
8.25–8.19 (m, 2H, ArH), 7.86–7.76 (m, 4H, ArH), 7.47 (d, J =
8.0 Hz, 2H, ArH), 7.26 (d, J = 8.8 Hz, 2H, ArH), 6.07 (s, 1H,
CH), 2.82 and 2.72 (AB system, J = 17.6 Hz, 2H, CHaCHbC
(CH3)2), 2.40 and 2.28 (AB system, J = 16.8 Hz, 2H,
CHaCHbCO), 1.18 (s, 3H, CH3), 1.10 (s, 3H, CH3); 13C NMR
(100 MHz, CDCl3): δ = 196.80, 163.68, 146.91, 144.02, 142.49,
141.65, 140.94, 140.80, 130.90, 130.80, 129.97, 129.92, 129.58,
129.42, 129.30, 128.50, 126.33, 125.49, 121.97, 120.03, 115.65,
16-(4-Hydroxy-3-methoxyphenyl)-3,3-dimethyl-2,3,4,16-tetra-
hydro-1H-benzo[a]chromeno[2,3-c]phenazin-1-one (2l). 1H NMR
(400 MHz, DMSO-d6) δ = 9.15–9.14 (m, 1H, ArH), 8.64 (s, 1H,
OH), 8.33–8.27 (m, 2H, ArH), 8.23–8.21 (m, 1H, ArH),
7.95–7.83 (m, 4H, ArH), 7.20–7.19 (m, 1H, ArH), 6.66–6.64
(m, 1H, ArH), 6.47–6.45 (m, 1H, ArH), 5.77 (s, 1H, CH),
3.68 (s, 3H, OCH3), 2.83 (s, 2H, CHaCHbC(CH3)2), 2.42 (d,
J = 16.1 Hz, 1H, CHaCHbCO), 2.23 (d, J = 16.1 Hz, 1H,
CHaCHbCO), 1.12 (s, 3H, CH3), 1.05 (s, 3H, CH3); 13C NMR
(100 MHz, DMSO-d6): δ = 196.47, 163.84, 146.74, 146.30,
144.89, 141.80, 141.10, 140.04, 135.81, 130.83, 130.54, 130.19,
129.69, 129.15, 128.81, 125.85, 124.79, 121.97, 120.12, 116.06,
115.09, 113.37, 113.50, 55.55, 50.21, 32.11, 29.09, 26.53;
IR (νmax cm−1) (KBr): 3431, 2958, 2834, 1655, 1370, 1202,
1174; MS (ESI) m/z calcd for C32H26N2O4: 502.19, found:
503.28 [M+ + H].
114.64, 50.90, 41.26, 33.31, 32.45, 29.43, 27.40; IR (νmax cm−1
)
(KBr): 2956, 1657, 1370, 1208; MS (ESI) m/z calcd
for C31H23BrN2O2: 534.09, found: 535.19 [M+ + H], 537.19
[M+ + H + 2].
16-(3-Chlorophenyl)-3,3-dimethyl-2,3,4,16-tetrahydro-1H-
benzo[a]chromeno[2,3-c]phenazin-1-one (2i). 1H NMR (400 MHz,
CDCl3) δ = 9.37–9.34 (m, 1H, ArH), 8.3 (d, J = 7.32 Hz, 2H,
ArH), 8.26–8.22 (m, 2H, ArH), 7.87–7.76 (m, 4H, ArH),
7.54–7.50 (m, 2H, ArH), 7.09–7.05 (m 1H, ArH), 6.99–6.96
(m, 1H, ArH), 6.09 (s, 1H, CH), 2.86 and 2.73 (AB system,
J = 17.6 Hz, 2H, CHaCHbC(CH3)2), 2.40 and 2.30 (AB system,
J = 16.1 Hz, 2H, CHaCHbCO), 1.18 (s, 3H, CH3), 1.12 (s, 3H,
CH3); 13C NMR (100 MHz, CDCl3): δ = 196.80, 163.86,
146.88, 142.49, 140.93, 133.65, 130.00, 129.93, 129.59, 129.40,
129.17, 128.98, 128.54, 127.43, 126.44, 125.48, 122.05, 114.48,
50.91, 41.26, 33.56, 32.49, 29.35, 27.48; IR (νmax cm−1) (KBr):
3055, 2929, 2880, 1659, 1374, 1201, 1170, 1042; MS (ESI) m/z
calcd C31H23ClN2O2: 490.14, found: 491.22 [M+ + H], 493.22
[M+ + H + 2].
3,3-Dimethyl-16-(thiophen-2-yl)-2,3,4,16-tetrahydro-1H-benzo-
[a]chromeno[2,3-c]phenazin-1-one (2m). 1H NMR (400 MHz,
CDCl3) δ = 9.34–9.31 (m, 1H, ArH), 8.34–8.24 (m, 3H, ArH),
7.84–7.77 (m, 4H, ArH), 7.09 (d, J = 3.6 Hz, 1H, ArH), 6.95 (d,
J = 5.1 Hz, 1H, ArH), 6.74–6.72 (m, 1H, ArH), 6.50 (s, 1H,
CH), 2.85 and 2.72 (AB system, J = 17.6 Hz, 2H, CHaCHbC-
(CH3)2), 2.42 (s, 2H, CHaCHbCO), 1.22 (s, 3H, CH3), 1.18 (s,
3H, CH3); 13C NMR (100 MHz, CDCl3): δ = 196.76, 164.32,
148.54, 146.97, 142.45, 141.59, 140.99, 140.81, 130.80, 129.96,
129.85, 129.53, 129.40, 128.42, 126.42, 126.32, 125.40. 125.34,
123.59, 121.96, 115.66, 114.57, 50.94, 41.24, 32.37, 29.52,
28.03, 27.61; IR (νmax cm−1) (KBr): 2928, 1648, 1373, 1201;
MS (ESI) m/z calcd for C29H22N2O2S: 462.14, found: 463.21
[M+ + H].
16-(4-Methoxyphenyl)-3,3-dimethyl-2,3,4,16-tetrahydro-1H-
benzo[a]chromeno[2,3-c]phenazin-1-one (2n). 1H NMR (400 MHz,
CDCl3) δ = 9.35–9.33 (m, 1H, ArH), 8.37 (d, J = 8.76 Hz, 1H,
ArH), 8.24–8.23 (m, 2H, ArH), 7.85–7.76 (m, 4H, ArH),7.51
(d, J = 8.8 Hz, 2H, ArH), 6.68 (d, J = 8.8 Hz, 2H, ArH), 6.08
(s, 1H, CH), 3.63 (s, 3H, OCH3), 2.83 and 2.72 (AB system,
J = 16.8 Hz, 2H, CHaCHbC(CH3)2), 2.40 and 2.29 (AB system,
J = 16.8 Hz, 2H, CHaCHbCO), 1.18 (s, 3H, CH3), 1.12 (s, 3H,
CH3); 13C NMR (100 MHz, CDCl3): δ = 196.94, 163.44,
157.79, 146.79, 142.65, 142.36, 141.84, 140.88, 137.25, 129.90,
129.79, 129.42, 128.26, 125.43, 121.90, 116.51, 115.21, 113.22,
3,3-Dimethyl-16-(naphthalen-2-yl)-2,3,4,16-tetrahydro-1H-
benzo[a]chromeno[2,3-c]phenazin-1-one (2j). 1H NMR (400 MHz,
CDCl3) δ = 9.50 (d, J = 8.0 Hz, 1H, ArH), 9.31 (d, J = 8.0 Hz,
1H, ArH), 8.42 (d, J = 7.3 Hz, 1H, ArH), 8.14–8.12 (m, 1H,
ArH), 7.87–7.78 (m, 4H, ArH), 7.71–7.61 (m, 3H, ArH),
7.53–7.48 (m, 2H, ArH), 7.32–7.30 (m, 1H, ArH), 7.15–7.11
(m,1H, ArH), 6.79 (s, 1H, CH), 2.86 and 2.76 (AB system,
J = 17.6 Hz, 2H, CHaCHbC(CH3)2), 2.36 and 2.21 (AB system,
J = 16.1 Hz, 2H, CHaCHbCO), 1.18 (s, 3H, CH3), 1.06 (s, 3H,
CH3); 13C NMR (100 MHz, CDCl3): δ = 196.99, 163.01,
146.80, 142.42, 142.02, 140.83, 131.33, 131.84, 130.70, 129.85,
129.63, 129.27, 129.15, 128.30, 127.81, 127.11, 126.89, 126.65,
125.51, 125.39, 125.16, 124.87, 121.94, 117.84, 116.31, 50.77,
41.30, 32.40, 29.40, 27.37; IR (νmax cm−1) (KBr): 2928, 1600,
1367, 1200, 1175; MS (ESI) m/z calcd for C35H26N2O2: 506.19,
found: 507.28 [M+ + H].
54.99, 50.97, 41.25, 32.67, 32.46, 29.44, 27.43; IR (νmax cm−1
)
(KBr): 2927, 1601, 1375, 1202; MS (ESI) m/z calcd for
C32H26N2O3: 486.19, found: 487.28 [M+ + H].
15-(4-Methylphenyl)-2,3-dihydrobenzo[a]cyclopenta[5,6] pyrano-
[2,3-c]phenazin-1-(15H)-one (2o). 1H NMR (400 MHz, CDCl3)
δ = 9.33–9.30 (m, 1H, ArH), 8.41–8.38 (m, 1H, ArH),
8.23–8.19 (m, 1H, ArH), 8.14–8.10 (m, 1H, ArH), 7.85–7.73
(m, 4H, ArH), 7.35 (d, J = 8.0 Hz, 2H, ArH), 6.95 (d, J = 7.32
Hz, 2H, ArH), 5.90 (s, 1H, CH), 3.04–2.97 (m, 1H, CH),
2.94–2.88 (m, 1H,CH), 2.61–2.58 (m, 2H, CH), 2.14 (s, 3H,
CH3); 13C NMR (100 MHz, CDCl3): δ = 202.37, 176.85,
148.08, 142.44, 141.86, 140.95, 140.82, 135.89, 131.03, 129.93,
129.83, 129.63, 129.44, 129.30, 128.72, 128.53, 126.46,
125.41, 122.07, 120.43, 115.57, 34.24, 34.03, 25.45, 20.98;
IR (νmax cm−1) (KBr): 2925, 2854, 1669, 1373, 1232; MS (ESI)
m/z calcd for C29H20N2O2: 428.15, found: 429.22 [M+ + H].
16-(4-Isopropylphenyl)-3,3-dimethyl-2,3,4,16-tetrahydro-1H-
benzo[a]chromeno[2,3-c]phenazin-1-one (2k). 1H NMR (400 MHz,
CDCl3) δ = 9.16–9.14 (m, 1H, ArH), 8.35–8.33 (m, 1H, ArH),
8.26–8.21 (m, 2H, ArH), 7.94–7.83 (m, 4H, ArH), 7.36 (d,
J = 8.0 Hz, 2H, ArH), 6.97 (d, J = 8.0 Hz, 2H, ArH), 5.85 (s,
1H, ArH), 2.8 (s, 2H, CH2), 2.65–2.59 (m, 1H, CHC(CH3)2),
2.40–2.36 (m, 1H, CH2), 2.22–2.18 (m, 1H, CH2), 1.11 (s, 3H,
CH3), 1.02 (s, 3H, CH3), 0.98 (d, J = 6.6 Hz, 6H, CHC(CH3)2);
IR (νmax cm−1) (KBr): 2958, 1656, 1371, 1204; MS (ESI) m/z
calcd for C34H30N2O2: 498.23, found: 499.22 [M+ + H].
Green Chem.
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15-(4-Methoxyphenyl)-2,3-dihydrobenzo[a]cyclopenta[5,6]-
pyrano[2,3-c]phenazin-1-(15H)-one (2p). Yellow solid; 1H NMR
(400 MHz, CDCl3) δ = 9.35–9.33 (m 1H, ArH), 8.42–8.40 (m,
1H, ArH), 8.24–8.22 (m, 1H, ArH), 7.86–7.75 (m, 4H, ArH),
7.39 (d, J = 8.7 Hz, 2H, ArH), 6.68 (d, J = 8.8 Hz, 2H, ArH),
5.91 (s, 1H, ArH), 3.63 (s, 3H, OCH3), 3.05–2.99 (m, 1H, CH2),
2.94–2.90 (m, 1H, CH2), 2.61–2.60 (m, 2H, CH2); IR
(νmax cm−1) (KBr): 2925, 1665, 1371, 1229; MS (ESI) m/z calcd
for C29H20N2O3: 444.15, found: 445.22 [M+ + H].
CDCl3) δ = 9.26–9.24 (m, 1H, ArH), 8.38–8.36 (m, 1H, ArH),
8.33 (s, 1H, ArH), 8.26 (s, 1H, ArH), 7.89–7.80 (m, 2H, ArH),
7.46 (d, J = 8.0 Hz, 2H, ArH), 7.12 (d, J = 8.7 Hz, 2H, ArH),
5.9 (s, 1H, CH), 3.00–2.93 (m, 1H, CH2), 2.89–2.81 (m, 1H,
CH2), 2.53–2.42 (m 2H, CH2), 2.21–2.09 (m, 2H, CH2);
IR (νmax cm−1) (KBr): 2923, 2852, 1649, 1369, 1177, 1022;
MS (ESI) m/z calcd for C29H17Cl3N2O2: 530.03, found: 531.12
[M+ + H], 533.14 [M+ + H + 2].
15-(3-Chlorophenyl)-2,3-dihydrobenzo[a]cyclopenta[5,6]pyrano-
[2,3-c]phenazin-1-(15H)-one (2q). 1H NMR (400 MHz, CDCl3)
δ = 9.39–9.37 (m 1H, ArH), 8.47–8.45 (m, 1H, ArH), 8.26–8.24
(m, 1H, ArH), 8.15–8.14 (m, 1H, ArH), 7.90–7.84 (m, 2H,
ArH), 7.80–7.77 (m, 2H, ArH), 7.47–7.45 (m, 1H, ArH), 7.37
(s, 1H, ArH), 7.12–7.08 (m, 1H, ArH), 7.01–6.98 (m, 1H, ArH),
5.94 (s, 1H, CH), 3.08–3.03 (m, 1H, CH2), 2.97–2.93 (m, 1H,
CH2), 2.62–2.59 (m, 2H, CH2); IR (νmax cm−1) (KBr): 2925,
1668, 1380, 1233, 1127, 1029; MS (ESI) m/z calcd for
C28H17ClN2O2: 448.10, found: 449.12 [M+ + H], 451.12
[M+ + H + 2].
Acknowledgements
AC and BN thank C.S.I.R., New Delhi, India for the grant of
senior research fellowship. AL is thankful to University of
Delhi, India for the grant of UTA.
Notes and references
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12,13-Dichloro-16-(4-chlorophenyl)-3,3-dimethyl-2,3,4,16-tetra-
hydro-1H-benzo[a]chromeno[2,3-c]phenazin-1-one (2r). 1H NMR
(400 MHz, CDCl3) δ = 9.26–9.24 (m, 1H, ArH), 8.37–8.33
(m, 2H, ArH), 8.27 (s, 1H, ArH), 7.89–7.80 (m, 2H, ArH), 7.47
(d, J = 8.8 Hz, 2H, ArH), 7.12 (d, J = 8.8 Hz, 2H, ArH), 5.97
(s, 1H, CH), 2.82 and 2.72 (AB system, J = 17.6 Hz, 2H,
CHaCHbC(CH3)2), 2.40 and 2.28 (AB system, J = 16.1 Hz, 2H,
CHaCHbCO), 1.18 (s, 3H, CH3), 1.09 (s, 3H, CH3); 13C NMR
(100 MHz, CDCl3): δ = 196.74, 163.44, 143.15, 142.39, 141.52,
140.93, 139.39, 134.69, 134.06, 131.93, 130.50, 130.27, 129.72,
129.51, 128.85, 128.80, 126.52, 125.64, 122.17, 115.40, 114.65,
50.84, 41.17, 33.16, 32.46, 29.41, 27.35; IR (νmax cm−1) (KBr):
1655, 1369, 1211, 1194, 1045; MS (ESI) m/z calcd
for C31H21Cl3N2O2: 558.06, found: 559.16 [M+ + H], 561.15
[M+ + H + 2].
12,13-Dichloro-3,3-dimethyl-16-(4-methylphenyl)-2,3,4,16-tetra-
hydro-1H-benzo[a]chromeno[2,3-c]phenazin-1-one (2s). 1H NMR
(400 MHz, CDCl3) δ = 9.20–9.18 (m, 1H, ArH), 8.35–8.33 (m,
1H, ArH), 8.28–8.27 (m, 2H, ArH),7.84–7.78 (m, 2H, ArH),
7.42 (d, J = 8.0 Hz, 2H, ArH), 6.96 (d, J = 8.0 Hz, 2H, ArH),
5.96 (s, 1H, CH), 2.82 and 2.72 (AB system, J = 17.6 Hz, 2H,
CHaCHbC(CH3)2), 2.40 and 2.29 (AB system, J = 16.1 Hz, 2H,
CHaCHbCO), 2.14 (s, 3H, CH3), 1.19 (s, 3H, CH3), 1.11 (s, 3H,
CH3); 13C NMR (100 MHz, CDCl3): δ = 196.79, 163.25,
147.56, 142.60, 141.65, 140.94, 139.28, 135.86, 134.35, 133.81,
130.38, 129.62, 128.78, 128.67, 128.60, 126.71, 15.55, 122.07,
116.11, 115.14, 50.91, 41.19, 33.09, 32.46, 29.45, 27.42, 20.98;
IR (νmax cm−1) (KBr): 2924, 2865, 1666, 1370, 1209; MS (ESI)
m/z calcd for C32H24Cl2N2O2: 538.12, found: 539.21 [M+ + H],
541.21 [M+ + H + 2].
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12,13-Dichloro-16-(4-chlorophenyl)-2,3,4,16-tetrahydro-1H-
benzo[a]chromeno[2,3-c]phenazin-1-one (2t). 1H NMR (400 MHz,
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