Synthesis of tetracyclic aza-/oxa-naphthalen-8-ones and their antimicrobial activity

Article abstract of DOI:10.1007/s00044-012-0425-z

Tetracyclic azanaphthalen-8-ones are synthesized by condensing 3-bromo-4-methyl benzo[h]-chromen-2-one with different primary aromatic amines. 3-Bromo-4-methylbenzo[h]chromen-2-one is synthesized by bromination of 4-methylbenzo[h]chromen-2-one using N-bromosuccinimide. Condensation of 3-bromo-4-methylbenzo[h]chromen-2-one with different secondary cyclic amines gave tetracyclic oxa-naphthalen-9-one. All the synthesized compounds were screened for their antimicrobial activity and they show good results.

Full text of DOI:10.1007/s00044-012-0425-z

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2013) 22:4223–4227
DOI 10.1007/s00044-012-0425-z
ORIGINAL RESEARCH
Synthesis of tetracyclic aza-/oxa-naphthalen-8-ones and their
antimicrobial activity
•
Shubhangi S. Soman Tirth H. Thaker
Received: 28 May 2011 / Accepted: 15 December 2012 / Published online: 3 January 2013
Ó Springer Science+Business Media New York 2012
Abstract Tetracyclic azanaphthalen-8-ones are synthesized
by condensing 3-bromo-4-methyl benzo[h]-chromen-2-one
with different primary aromatic amines. 3-Bromo-4-meth-
ylbenzo[h]chromen-2-one is synthesized by bromination of
4-methylbenzo[h]chromen-2-oneusingN-bromosuccinimide.
Condensation of 3-bromo-4-methylbenzo[h]chromen-2-one
with different secondary cyclic amines gave tetracyclic oxa-
naphthalen-9-one. All the synthesized compounds were
screened for their antimicrobial activity and they show good
results.
cholesterol synthesis. Considering the above results and in
continuation of our work on benzo pyrone derivatives
(Soman, 2004; Patel and Soman, 2010; Soman and Thaker,
2009), this report extends investigation on the synthesis of
tetracyclic aza/oxa-naphthalen-8-ones and detailing bio-
logical activity of the synthesized compounds.
Results and discussion
Pechmann condensation (Robertson et al., 1931) of a-naphthol
with ethylacetoacetate gave 4-methyl-benzo[h]chromen-2-one
1. Bromination of 1 with N-bromosuccinimide in the presence
of benzoyl peroxide and light (100 W bulb) in refluxing chlo-
roform was expected to give 4-bromomethylbenzo[h]chro-
men-2-one, instead gave 3-bromo-4-methylbenzo[h]chromen-
2-one 2. The structure of 2 was confirmed by IR, 1H-NMR and
mass spectra. In 1H-NMR of 1, the presence of a sharp singlet at
d 6.35 integrated for one proton clearly indicated C-3 proton,
singlet at d 2.50 integrated for three protons indicated methyl
Keywords a-Naphthol ꢀ Azanaphthalen-8-ones ꢀ
Oxanaphthalen-8-one ꢀ Biological activity
Introduction
Naphthopyrones are reported to possess various biological
activities (Braccio et al., 2003; Braccio et al., 1995; Roma
et al., 1998). Several furonaphthopyrones are reported to
possess DNA-intercalating properties (Fu et al., 1999a;
Xuhong et al., 1996 Fu et al., 1996). Furo- and thion-
aphthopyrones have been reported as potential mono
functional photo biological agents (Fu and Xuhong, 1998;
Fu and Xuhong, 1996; Fu et al., 1999b) to DNA. Pannorin,
a derivative of naphthopyrone, a new coenzyme A reduc-
tase inhibitor produced by chrysosporium pannorum
(Haruo et al., 1991), is the rate limiting enzyme in
1
group at C-4. After bromination in the H-NMR of 2, sharp
singlet integrated for one proton at d 6.35 was disappeared and
methyl signal for three protons at d 2.71 was clearly observed.
All other aromatic protons were observed in the range of d
7.62–8.56. This indicated bromination with N-bromosuccini-
mide has occurred at third position of chromen-2-one. More-
over, mass spectrum of 2 also supported with M?2: M? (1:1)
signal at 291 and 289. Reference [15–18] (Bacovescu, 1910;
Dey and Lakshminarayanan, 1934; Carnduff and Marks, 1977;
Carnduff and Marks, 1975)-reported bromination of 1-Meth-
ylbenzo[f]chromen-3-one with bromine in acetic acid gave
3-bromo-1-methylbenzo[f]chromen-3-one.
S. S. Soman (&) ꢀ T. H. Thaker
We had condensed 2 with different primary aromatic
amines expecting to get 4-aminomethyl derivatives of benzo-
[h]-chromen-2-ones, as we had prepared furopsoralenamines
Department of Chemistry, Faculty of Science,
The M. S. University of Baroda, Vadodara 390002, India
e-mail: shubhangiss@rediffmail.com
123

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Med Chem Res (2013) 22:4223–4227
(Patel and Soman, 2010). But, to our surprise, the product
obtained was tetracyclic (3 a–d). Carnduff (Carnduff and
Marks, 1977; Carnduff and Marks, 1975) observed that alka-
line hydrolysis of 2-Bromo-1-methylbenzo[f]chromen-3-one
gave two unusual products involving skeletal rearrangement. 2
on condensation with p-toluidine gave 9-p-Tolyl-6b,7,9,9a-
tetrahydro-10-oxa-9-aza-pentaleno[2,1-a]naphthalene-8-one
(3a). The structure of this compound was confirmed by IR and
1H-NMR analyses Scheme 1 (Soman and Thaker, 2010).
In 1H-NMR, a singlet for three protons at d 2.39 indicated
–CH3, two double doublets integrated for one proton each at
d 2.82–2.88 with J = 2.4 Hz and d 3.15–3.24 with J = 3.4,
9.6 Hz clearly indicated –CH2 proton, while the multiplet at
d 4.34–4.39 for one proton indicated proton at ring junction.
The doublet for one proton at d 6.60–6.63 indicated another
proton at ring junction, sandwiched between O and N. Sig-
nals from d 7.26–7.96 indicated other aromatic protons. The
IR spectrum showed carbonyl band at 1,709 cm-1, which
indicated cyclic five-membered amide.
The formation of 3 a–d was further supported by the fact
that when this reaction was carried out in solvent like
absolute ethanol, the starting material 3-Bromo-4-meth-
ylbenzo[h]chromen-2-one was recovered. When dimeth-
ylformamide (DMF) was used as solvent reaction gave the
product.
When we have condensed different cyclic secondary
amines like morpholine and N-methyl piperazine with 2, it
gave the only product 4 which was showing same 1H-NMR
pattern as 3 a–d. Its IR spectrum showed carbonyl stretching
frequency at 1,770 cm-1. Moreover, Lassaigne’s test and
elemental analysis of product 4 indicated the absence of
nitrogen. Since nitrogen is absent in the sample, it indicated
the five-membered lactone ring which is supported by IR
stretching frequency at 1,770 cm-1. Thus, the formation of
6b,9a-Dihydro-7H-9,10-dioxa-pentaleno[2,1-a]naphtha-
lene-8-one 4 was confirmed. Further formation of this
product was supported by single crystal analysis of 10, 10a-
Dihydro-7aH-7,8-dioxa-pentaleno[1,2-a]naphthalen-9-one,
which was formed when we have condensed morpholine
with 2-bromo-1-methylbenzo[f]chromen-3-one (Soman and
Thaker, 2010), the CCDC no. of which is 766459.
Formation of similar product was confirmed by single
crystal analysis of 8-p-Tolyl-7a,8,10,10a-tetrahydro-7-oxa-
8-aza-pentaleno[1,2-a]naphthalen-9-one which was formed
upon condensation of p-toluidine with 2-bromo-1-meth-
ylbenzo[f]chromen-3-one (Soman and Thaker, 2010), the
CCDC no. of which is 766458.
The formation of cyclic lactone 4 indicated that water
must be attacking and the secondary amine is eliminated
during reaction. Thus, we have observed the formation of
tetracyclic ring during the condensation of 3-bromo-4-
methyl benzo[h]chromen-2-one with primary aromatic
amines as well as secondary cyclic amines. Mashelkar
Similar compounds 3 a–d were obtained when different
primary aromatic amines were condensed like aniline,
p-toluidine, m-nitro aniline and p-nitro aniline with 2.
Scheme 1
O
O
Br
O
O
NBS/CHCl3
Benzoyl Peroxide
CH3
CH3
2
1
NH2
H
N
R=-H,-p CH
3,-p NO2 ,-m NO2
DMF
DMF
R
O
O
O
R
3a R=-CH3
N
3b R=
3c R=
-H
O
O
-p
NO2
4
3d R= -m NO2
3a-d
N
H
N
=
O
N
H
H
N
,
123

Med Chem Res (2013) 22:4223–4227
4225
et al. (2001)) reported the formation of tetracyclic product
by oxidation of benzocoumarin-4-acetic acid with selenium
dioxide and further reactions.
1H, C10-H). Mass: M?2: M? (1:1) 291, 289(b), 245, 260,
211(M-Br), 181, 152. Anal. Calcd. for C14H9O2Br (288.5):
C, 58.23; H, 3.11. Found: C, 58.12; H, 3.30.
It was thought that these novel products obtained in the
case of b-naphthol (Soman and Thaker, 2010) may be due
to the steric hinderance of naphthalene ring, which may not
be observed in the case of a-naphthol because the lactone
ring at the 3rd position is not sterically hindered. But
similar results were obtained (Soman and Thaker, 2010)
General procedure for the preparation of aza
naphthalen-8-ones (3a–d)
A mixture of 2 (0.01 mol), different primary aromatic
amines (0.021 mol) and DMF (20 ml) was refluxed for 6 h.
The reaction mixture was cooled, poured into crushed ice
and filtered. The crude product was purified by column
chromatography using petroleum ether: ethyl acetate (9:1)
as eluent.
1
which was supported by IR and H-NMR of products.
Experimental
The melting points were determined in scientific open
capillaries and are uncorrected. The IR spectra were
determined as KBr pellets on a Schimadzu model IR-408
9-p-Tolyl-6b,7,9,9a-tetrahydro-10-oxa-9-aza-
pentaleno[2,1-a]naphthalen-8-one (3a)
1
spectrophotometer. The H-NMR and 13C NMR spectra
were recorded using Bruker DRX 400 MHz in CDCl3 or
DMSO-d6 with tetramethylsilane as internal standard. Mass
spectra were recorded on a GC–MS spectrometer. Ele-
mental analyses were performed on Carlo Erba-1108 ele-
mental analyser. Acme’s Silica gel (mesh size 60–120) was
used for column chromatography.
Yield 21 %, mp 132-133 °C. IR (KBr): mmax, cm-1: 3055,
2920, 1716, 1613, 1514, 1469, 1443, 1382, 1263. 1H-NMR
(CDCl3, 400 MHz): d 2.39 (s, 3H, CH3), 2.82–2.88 (dd, 1H,
J1 = 2.4 Hz, H at –CH2), 3.15–3.24 (dd,1H, J = 9.6 Hz, H
at –CH2), 4.34–4.39 (m, 1H, J = 7.5 Hz, H at ring junc-
tion), 6.60–6.63 (d, 1H, J = 7.2 Hz, H at ring junction),
7.26–7.28 (d, 1H, J = 5.74 Hz, C2,C5-H), 7.34–7.37 (d,
1H, J = 8.4 Hz, C4-H), 7.46–7.55 (m, 5H, C1, C3, C6, C30,
C50-H), 7.83–7.86 (m, 1H, C20-H), 7.93–7.96 (m, 1H, C60-
H) Anal. Calcd. for: C21H17 NO2 (315): C, 80.00; H, 5.39;
N, 4.44. Found: C, 79.91; H, 5.51; N, 4.30.
4-Methylbenzo[h]chromen-2-one 1
In the mixture of a-naphthol (10 gm, 0.0,694 mol) and
ethylacetoacetate (9.0 ml, 0.0,694 mol), H2SO4 (20 ml)
was added slowly with constant stirring and allowed to
keep overnight. It was poured into crushed ice with con-
stant stirring. The crude product filtered and recrystallized
from ethanol as yellow crystals. Yield 53 %, mp ref. [14]
165–167 °C. IR (KBr): mmax, cm-1: 3071, 2923, 2854,
9-p-Phenyl-6b,7,9,9a-tetrahydro-10-oxa-9-aza-
pentaleno[2,1-a]naphthalen-8-one (3b)
Yield 39 %. mp 208–210 °C. Anal. Calcd. for: C20H15NO2
(301): C, 79.73; H, 4.98; N, 4.65. Found: C, 79.53; H, 4.79;
N, 4.77.
1
1716, 1610, 1504, 1377. H-NMR (CDCl3, 400 MHz) d
2.50 (s, 3H, CH3), 6.35 (s, 1H, C3-H), 7.58–7.87 (m, 5H,
C5, C6, C7, C8, C9-H), 8.51–8.56 (m, 1H, C10-H). Anal.
Calcd. for C14H10O2 (210): C, 80.00; H, 4.76. Found: C,
80.11; H, 4.59.
9-p-Nitrophenyl-6b,7,9,9a-tetrahydro-10-oxa-9-aza-
pentaleno[2,1-a]naphthalen-8-one (3c)
3-Bromo-4-methylbenzo[h]chromen-2-one 2
Yield 30 %, mp 237–239 °C. IR (KBr): mmax, cm-1: 3066,
1719, 1635, 1598, 1516, 1472, 1377, 1344, 1136, 1088. 1H-
NMR (CDCl3, 400 MHz): d 2.99–3.05 (dd, 1H, J = 3.8 Hz,
H at –CH2), 3.34–3.41 (dd, 1H, J = 10.1 Hz, H at –CH2),
4.56–4.62 (m, 1H, J1 = 3.7, J2 = 7.1 Hz, H at ring junc-
tion), 6.77–6.79 (d, 1H, J = 7.9 Hz, H at ring junction),
7.13–7.15 (d, 1H, J = 8.8 Hz, C5-H), 7.39–7.43(m, 1H, C2-
H), 7.55–7.62 (m, 2H, J = 8.8 Hz, C3, C4-H), 7.78–7.79 (m,
2H, C1, C6-H), 8.10–8.12 (d, 2H, J = 9.2 Hz, C20, C60-H),
8.30–8.32 (d, 2H, J = 9.4 Hz, C30, C50-H). Anal. Calcd. for
C20H14N2O4 (346): C, 69.36; H, 4.04; N, 8.09. Found: C,
69.16; H, 4.24; N, 8.21.
To a solution of 1 (2 gm, 0.0095 mol) dissolved in 25 ml
chloroform, N-bromosuccinimide (1.7 gm, 0.0095 mol)
and a 10 mg benzoyl peroxide (catalytic amount as an
initiator) were added and refluxed in a photoreactor for
10 h. using 100-W bulb. It was filtered, the excess solvent
distilled off, crude product filtered and washed with
methanol and recrystallized from toluene. Yield 73 %, mp
192–193 °C. IR (KBr): mmax, cm-1: 3160, 3072, 1714,
1635, 1610, 1375, 1294, 1193, 851, 810. 1H-NMR (CDCl3,
400 MHz) d: 2.71 (s, 3H, –CH3), 7.62–7.73 (m, 4H, C6,
C7, C8, C9-H), 7.86–7.88 (m, 1H, C5-H), 8.54–8.56 (m,
123

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Med Chem Res (2013) 22:4223–4227
Table 1 Zone of inhibition in
mm (antibacterial activity)
Compound
Staphylococcus aureus
Escherichia coli
Micrococcus luteus
mm
MIC
mm
MIC
mm
MIC
3a
11
10
08
21
10
05
250
250
300
200
250
25
10
11
08
09
11
04
300
300
300
400
300
25
18
11
10
09
10
05
250
300
300
400
300
25
3b
3c
3d
4
Ampicillin
9-m-Nitrophenyl-6b,7,9,9a-tetrahydro-10-oxa-9-aza-
activity against all types of Gram positive and Gram negative
strains.
pentaleno[2,1-a]naphthalen-8-one (3d)
Yield 49 %, mp 141–143 °C. IR (KBr): mmax, cm-1: 3412,
3070, 2925, 1719, 1630, 1528, 1475, 1378, 1267, 1143,
1085, 811, 738. Anal. Calcd. for: C20H14 N2O4 (346): C,
69.36; H, 4.04; N, 8.09. Found: C, 69.41; H, 4.21; N, 8.11.
Experimental
Antibacterial activity of all the synthesized compounds was
tested in vitro by (cup plate method) serial agar dilution in
which bacterial strains of S. aureus (Gram positive), E. coli
(Gram negative) and M. luteus (Gram positive) were used,
using serial agar dilution (cup plate method).
General procedure for the preparation of 6b, 9a-Dihydro-
7H-9, 10-dioxa-pentaleno[2,1-a]naphthalen-8-one (4)
The two microorganisms were cultured in petri dishes
containing agar medium, cups (8 mm) were put onto the
dishes and each synthesized compound dissolved in DMF
(0.1 ml of 10 mg/ml) was added into the cups under aseptic
condition. Then, the petri dishes were incubated at 37 °C
for 24 h. The zone of inhibition of the growth of the bac-
teria, which were produced by diffusion of the compounds
from the cup into the surrounding medium, was measured
to evaluate the antibacterial activity. Each experiment was
repeated twice. DMF was used as a positive control for the
experiments. Results are shown in Table 1.
A mixture of 2 (0.01 mol) and different cyclic secondary
amines (0.021 mol) were refluxed in DMF (20 ml) for 6 h.
The reaction mixture cooled, poured into crushed ice and
filtered. The crude product was purified by column chro-
matography using petroleum ether: ethyl acetate (7:3) as
eluent. Yield 31 %, mp 84 °C. IR (KBr): mmax, cm-1: 3050,
1
1774([C=O), 1631, 1578, 1520, 1464. H-NMR (CDCl3,
400 MHz): d 2.96–3.02 (dd, 1H, J = 2.44 Hz, H at –CH2),
3.20–3.27 (dd, 1H, J = 9.84 Hz, H at –CH2), 4.53–4.58
(m, 1H, H at ring junction), 6.71–6.72 (d, 1H, J = 6.4 Hz,
H at ring junction), 7.19–7.21 (d, 1H, J = 8.8 Hz, C5-H),
7.39–7.44 (m, 1H, C2-H), 7.55–7.56 (d, 2H, C3, C4-H),
7.79–7.82 (d, 1H, J = 8.9 Hz, C6-H), 7.87–7.89 (d, 1H,
J = 8.2 Hz, C1-H). Anal. Calcd. for C14H10O3 (226): C,
74.33; H, 4.42. Found: C, 74.24; H, 4.59.
Antifungal activity
All the synthesized compounds were tested for their anti-
fungal activity by poison-food method [22] (Nene and
Thapliyal, 1979). They were tested against Fusarium
roseum, Alternaria sp. and Cladosporium sp. at 100 lg
concentration. DMF was used as control. All compounds
showed excellent antifungal activity against all fungi which
were used in experiment.
Biological activity
Aza/Oxa naphthalene-8-ones were screened for their anti-
bacterial and antifungal activity.
Experimental
Antibacterial activity
Antifungal activity of all the synthesized compounds were
tested in vitro in which fungal strains of F. roseum, Alter-
naria sp. and Cladosporium sp. were used using Potato
Dextrose Agar (PDA) medium (Poisoned Food Technique).
PDA was prepared as per M096 HiMedia laboratories.
The standard fungi F. roseum, Alternaria sp. and Clado-
sporium sp. culture were grown on PDA slants at room
All the synthesized compounds were tested for their anti-
bacterial activity against Escherichia coli (Gram negative),
Staphylococcus aureus (Gram positive) and Micrococcus
luteus (Gram positive) by cup plate method [21] (Barry,
1977) at 100 ppm concentration in DMF solvent. Ampicillin
was used as standard drug. All compounds showed excellent
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Med Chem Res (2013) 22:4223–4227
4227
Table 2 % Inhibition of growth
(antifungal activity) zone of
inhibition in mm
Compound
Fuserium roseum
Alternaria species
Cladosporium species
mm
MIC
mm
MIC
mm
MIC
3a
3b
3c
3d
4
50
45
25
25
45
200
200
250
250
200
60
200
200
250
200
200
–
–
–
–
57.5
30
55
–
200
–
75
37.5
65
200
their benzo fused derivatives and some related 2-aminochro-
mones. Farmaco 58:1083
temperature. Mycelial growth inhibition of F. roseum, Alter-
naria sp. and Cladosporium sp. were evaluated by the poi-
soned food technique, where the inhibition in growth of the
fungal strain was observed on PDA. The stock solution
(100 lg) was made from each of the test compounds using
DMF. The required % concentrations of the compounds (mg/
ml) were obtained by mixing the appropriate amount of the
stock solution with 20 ml of molten PDA. The amended PDA
was poured into petridishes and allowed to set.
Carnduff J, Marks RB (1975) Aryl migration in the exceptional
hydrolysis of a bromo pyrone. Tetrahedron Lett 46:4073
Carnduff J, Marks RB (1977) An exceptional hydrolysis of a
3-bromo-2-pyrone involving aryl group migration. J Chem Res
8:201
Dey BB, Lakshminarayanan AK (1934) 3-Amino and 3-hydroxy-b-
naphthopyrones. J Ind Chem Soc 11:373
Fu TZ, Xuhong
Q (1996) Synthesis of 2H–4,8-dimethylthie-
no[20,30,5,6]naphtho[1,2-b]pyran-2-one with potential photo bio-
logical activity to DNA. Phosporous, Sulfur Silicon Relat Elem
114(14):109
An inoculums of the fungus obtained from 7 days old
axenic culture, grown as above, was placed at the centre of
the amended agar medium. Each experiment was per-
formed in triplicate. The diameter of the fungal colony was
measured after 4 days and then 7 days at 26 ? 1 °C and
the % inhibition was calculated by the following equation:
The result has been shown in Table 2.
Fu TZ, Xuhong Q (1998) Synthesis of naphthopyrones as potential
monofunctional photo biological agents to DNA. Dyes Pigm 39(4):193
Fu TZ, Xuhong Q, Jun T, Fuheng C (1996) Synthesis, spectra and DNA
intercalation of 2H–4,9-dimethylfuro[20,30,5,6]naphtho[1,2-b]pyran-
2-one. Yingyoung Huaxue Bianji Weiyuanhui 13(4):34
Fu TZ, Cai FM, Xuwong Q (1999a) Synthesis of novel DNA-
intercalating naphthopyrone derivatives with improved water
solubility and photo physical properties. Monatschefte chemie
130(9):1109
% inhibition
Fu TZ, Xuhong Q, Mingcai F (1999b) Highly efficient photoinduced
DNA cleavage by naphthopyrone hydroperoxides. Bull Chem
Soc Jpn 72(7):1571
Haruo O, Keiji H, Kaoru S, Shigeo MAE (1991) Chryosporium
pannorum. J Antibiotics 44(7):762
growth area in reference ꢁ growth area in sample
¼
ꢂ 100
growth area in reference
Acknowledgments The authors are thankful to the Head, Depart-
ment of Chemistry, Faculty of Science, The M. S. University of
Baroda, for providing necessary facilities. One of the authors (THT)
is thankful to UGC, New Delhi, for financial assistance. The authors
are thankful to Sun Pharma Advance Research Centre (SPARC) and
Mashelkar UC, Bade AA, Teli LR (2001) Synthesis of some
4-formylcoumarins/benzocoumarins and potentially biologically
active Schiff bases. Part III. J Indian Counc Chemist 18(1):49
Nene YL, Thapliyal PL (1979) Fungicide in plant disease control.
Oxford and IBH Pub. & Co, New Delhi 507
1
SAIF, Panjab University for H-NMR and mass spectra. The authors
Patel JM, Soman SS (2010) Studies in synthesis of new psoralenam-
ines. J Heterocycl Chem 47:379
are also thankful to Prof. Arun Arya, Head, Department of Botany, for
antifungal activity and Dr. Jayshree Pohneker, Department of
Biochemistry for antibacterial activity.
Robertson A., Sandrocik WF., Hendry CB. (1931) Hydroxy-carbonyl
compounds. Part V. The preparation of coumarins and 1:4-Pyrones
from phenol, p-cresol, quinol and a-Naphthol. J. Chem. Soc. 2426
Roma G, Braccio MD, Grossi G, Marzano C, Simonato M, Bordin F
(1998) Pyran derivatives XX. 2-Amino chromone benzofused
derivatives with antiproliferative properties. Farmaco 53:494
Soman SS (2004) Synthesis of benzofuro-4-anilino-2H–1-benzopyran-
2-one and benzofuro-pyrano-2H–1-benzopyran-2-one. Indian J
Chem 43(B):624
Soman SS, Thaker TH (2009) Synthesis of new 3-(1-Aryl-2-thioxo-
3,4-Dihydro-2H-Imidazol-4-yl)chromen-2-ones. Indian J Het-
erocycl Chem 19:55
Soman SS, Thaker TH (2010) Synthesis of tetracyclic 8-aza-naphtha-
len-9-ones and oxa-naphthalen-9-one. J Chem Res 34:502
Xuhong Q, Fu TZ, Zhi WD, Jie S (1996) Synthesis, Crystal structure
and properties of 2H–4,8-dimethylfuro [20,30,5,6]naphtho[1,2-
b]pyran-2-one. A novel DNA intercalator. Monatshefte chemie
127(5):569
References
Bacovescu A (1910) Condensation of a- and b- naphthols with
acetoacetic ester. Ber Deut Chem Ges 43:1280
Barry AL (1977) The antimicrobial susceptibility test principle and
practices edited by Illuslea and Febiger, USA, 180. Biol Abstracts
64:25183
Braccio MD, Roma G, Leoncini G, Poggi M (1995) Pyran derivatives
part XIX. (Dialkylamino) substituted 1-benzopyranones and
naphthopyranones with platelet antiaggregating activity. Farma-
co 50:703
Braccio MD, Grossi G, Roma G, Marzano C, Baccicheffi F, Simonato
M, Bordin F (2003) Pyran derivatives part XXI. Antiproliferative
and cytotoxic properties of novel N-substituted 4-aminocoumarins
123