Thermolysis of Chlorovinyl Imines as an Alternate Route for the Synthesis of Pyranoquinolin-3-one and Pyranoacridin-3-one Derivatives

Article abstract of DOI:10.1002/jhet.2993

Synthesis of 3H-pyrano[3,2-f]quinolin-3-one and 3H-benzo[h]pyrano[3,2-a]acridin-3-one derivatives are described by the thermolysis of suitable chlorovinyl imine derivatives. The chlorovinyl imines were obtained by condensation of suitable β-chloro-α,β-unsaturated aldehydes and 6-aminocoumarin in methanol at 15°C. Compounds showed blue fluorescence in alkaline medium.

Full text of DOI:10.1002/jhet.2993

Month 2017 Thermolysis of Chlorovinyl Imines as an Alternate Route for the Synthesis
of Pyranoquinolin-3-one and Pyranoacridin-3-one Derivatives
*
Prasanta Patra
Department of Chemistry, Jhargram Raj College, Jhargram, 721507, India
*
E-mail: prasantaanupama1983@gmail.com
Received April 11, 2017
DOI 10.1002/jhet.2993
Published online 00 Month 2017 in Wiley Online Library (wileyonlinelibrary.com).
Synthesis of 3H-pyrano[3,2-f]quinolin-3-one and 3H-benzo[h]pyrano[3,2-a]acridin-3-one derivatives are
described by the thermolysis of suitable chlorovinyl imine derivatives. The chlorovinyl imines were obtained
by condensation of suitable β-chloro-α,β-unsaturated aldehydes and 6-aminocoumarin in methanol at 15°C.
Compounds showed blue fluorescence in alkaline medium.
J. Heterocyclic Chem., 00, 00 (2017).
INTRODUCTION
synthesize. Very recently, we have reported the synthesis
of some novel polynuclear pyridocoumarin derivatives [5]
by thermolysis of anil hydrochlorides derived from
various β-chloro-α,β-unsaturated aldehyde derivatives and
two equivalents of 6-aminocoumarin. In our present work,
The coumarin derivatives fused to azaheterocycles,
especially the pyridine nucleus, have been reported to
possess various biological activities [1,2] like antiallergic,
antidiabetic, analgesic, anti-hypertensive, anti-HIV, and
antimalarial properties. This makes such class of
compounds important target molecules for synthesis with
gradual increase of publications in the last few decades
[2]. Thermolysis of anil hydrochlorides has been
established as an effective method for the synthesis of
various polycyclic azaarenes in the last three to four
decades [3]. The anil hydrochloride derivatives
are obtained by reaction of one equivalent of β-chloro-
we report
a
modified method to synthesize
pyridocoumarin derivatives by thermolysis of chlorovinyl
derivatives derived from various β-chloro-α,β-unsaturated
aldehyde derivatives and one equivalent of 6-
aminocoumarin.
Coumarin-derived
fluorescent
chemosensors have been extensively applied in a variety
of fields. These sensors are effective for detection of many
species such as metal ions, anions, biothiols, enzymes,
amines and amino acids, chemical warfare agents,
proteins, hydroxyl radicals, polymerization and polymeric
micelles, DNA and RNA, oxygen, and titania [6a, 6b, 6c,
6d, 6e]. Coumarins, with the structure of benzopyrone
[6f], have many advantages including high fluorescence
quantum yield, large Stokes shift, excellent light stability,
and less toxicity. Therefore coumarins have been widely
used in the fields of biology and medicine, perfumes,
cosmetics, and fluorescent dyes. By far, coumarin
derivatives have been used as fluorescent probes of pH,
for detection of nitroxide, nitric oxide, and hydrogen
peroxide [6g, 6h, 6i]. Our intention is to check the
fluorescence property of these pyridocoumarin derivatives
synthesized. The results are discussed later.
α,β-unsaturated
aldehyde
derivatives
and
two
equivalents of aryl amine. Ray et al. observed that
reaction of 1-naphthylamine and 1-chloro-3,4-dihydro-2-
naphthaldehydes failed to form any anil hydrochlorides
but formed the simple Schiff bases (chlorovinyl imine
derivatives) [4]. Thermolysis of these chlorovinyl imines
also produced desired polycyclic azaarenes in very good
yield. The disadvantage of this method is that it is limited
to 1-naphthylamines. Other aryl amines produce anil
hydrochlorides, rather than chlorovinyl imine derivatives,
even when using the amine and chloroaldehydes in 1:1
ratio under normal condition, and one equivalent of
chloroaldehyde remained unreacted. Also the Schiff bases
prepared by other methods are not so stable and gradually
turned into anil derivatives on storage. Advantage of
thermolysis of chlorovinyl imines to prepare polycyclic
aza arenes (PAAs) is that here one equivalent of amine is
saved and sometime may be a better method especially
when the aryl amine component is costly or difficult to
RESULT AND DISCUSSIONS
In our present work, we have explored the preparation of
chlorovinyl imines and the general method for the
© 2017 Wiley Periodicals, Inc.

P. Patra
Vol 000
synthesis of pyridocoumarins through thermolysis of
chlorovinyl imines. Our first task was to find out an
optimal condition to prepare the chlorovinyl imines in the
best possible yield because the reaction of such
chloroaldehydes with aryl amines (other than 1-
naphthylamine derivatives) spontaneously formed anil
hydrochlorides instead of chlorovinyl imines [4].
Condensation between 5-methoxy α-tetralone (one
equivalent) and 6-aminocoumarin (one equivalent)
(Scheme 1) was studied under variation of solvents
(chloroform, benzene, MeOH, etc), additives (HCl,
Al2O3, NaHCO3, etc.), or temperature and time. Results
of the detailed studies are summarized in Table 1. It was
found that condensation of 1 and 2d in methanol at 15°C
without any acid/base catalyst proved to be the best
condition and leads to the desired product in 95% yield
within 30 min (Table 1, entry 5). Thus treatment of 6-
aminocoumarin (one equivalent) with different β-chloro-
α,β-unsaturated aldehyde derivatives (one equivalent)
proceeded to give the corresponding novel chlorovinyl
imine derivatives. IR spectra of compound 3d show
strong absorption band at 1625.4 and 1732.0 cmÀ1. The
1H NMR (300 MHz, CDCl3) data are in conformity with
the assigned structure for the chlorovinyl imine 3d and
given later (Fig. 1), and high-resolution mass
spectrometry (HRMS) data are also in agreement with the
structure of 3d. In HRMS, two distinct m/z peaks were
observed at 365.9783 for (M+ + H) and 367.9769 for
(M+ + H + 2) and indicate the presence of chlorine.
Reaction of other β-chloro-α,β-unsaturated aldehyde
derivatives 2(a–f) and 6-aminocoumarin under identical
condition produced respectively the chlorovinyl imine
derivatives 3(a–f) in excellent yields (Table 2). The
chlorovinyl imine derivatives were characterized by usual
spectroscopic data. When these chlorovinyl imine
derivatives were subjected to thermolysis, the desired
Scheme 1. Reaction of chloroaldehyde 2d with 6-aminocoumarin 1.
Table 1
Optimization studies in the selective formation of chlorovinyl imine 3d.
Entry no.
Reactants
Solvent
Additive
Temp (°C)
Time (h)
Product (3) (%)
Product (4) (%)
1
2
3
4
5
6
7
1a:1b
1a:1b
1a:1b
1a:1b
1a:1b
1a:2b
1a:1b
Benzene
Benzene
EtOH
NaHCO3
NaHCO3 + Al2O3
NaHCO3
HCl
—
Reflux
Reflux
Reflux
15°C
15°C
15°C
10
10
12
3
0.5
0.5
1
50
52
35
—
95
85
70
—
—
15
45
—
5
EtOH
MeOH
MeOH
CHCl3
—
—
15°C
—
rt = 15–20°C. Best optimized condition for the reported reaction is shown in bold entry.
a2d.
b1 in equivalent.
Figure 1. Chemical shifts (δ, ppm) in 1H NMR spectra of 3d.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2017
Thermolysis of Chlorovinyl Imines as an Alternate Route for the Synthesis of
Pyranoquinolin-3-one and Pyranoacridin-3-one Derivatives
Table 2
Formation of chlorovinyl imine and pyridocoumarin derivatives 3H-pyranoquinolin-3-one and 12,13-dihydro-3H-benzo[h]pyrano[3,2-a]acridin-3-one
derivatives.
Entry no.
1
Reactant
Chlorovinyl imine yield
Time (min)
30
Product(s) yield
2
3
60
50
4
5
30
30
6
50
PAA 5(a–f) in moderate to good yields was produced.
Thus compound of 3d when heated at about 230–260°C
for 15–20 min, without any solvent, furnished the novel
pyridocoumarin derivative 11-methoxy-12,13-dihydro-
3H-benzo[h]pyrano[3,2-a]acridin-3-one (5d) in 65% yield
after usual work-up (Scheme 2). IR spectra of compound
5d show strong absorption band at 1628.8 and
3(a–c, e, f) too on thermolysis produced the
pyridocoumarin derivatives 5(a–c, e, f), respectively, in
60–65% yields. Scheme
3 represents a plausible
mechanism [4] showing the formation of compound 5d
from 3d.
Fluorescence properties of reference compound 5d. The
fluorescence property of 5d as reference compound
(50 μM) was investigated in aqueous methanol at 25°C
(λexc = 350 nm) (Fig. 3). Compound 5d as such was
fluorescence silent in absence of hydroxide ion, although
fluorescence intensity of 5d significantly increased when
various concentrations of OHÀ (5–100 μM) were added
1
1729.0 cmÀ1. The H NMR (300 MHz, CDCl3) data are
in conformity with the assigned structure for the
pyridocoumarin 5d and given later (Fig. 2), and HRMS
data are also in agreement with the structure of 5d. The
method is a general one, and other chlorovinyl imines
Journal of Heterocyclic Chemistry
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P. Patra
Vol 000
Scheme 2. Cyclization of chlorovinyl imine 3d to 5d.
Figure 3. Emission spectra of 5d (40 mM) in the presence of various con-
centrations of aqueous OHÀ (λexc = 350 nm). [Color figure can be viewed
at wileyonlinelibrary.com]
1
Figure 2. Chemical shifts (δ, ppm) in H NMR spectra of 5d.
(Fig. 1). Upon gradual addition of aqueous OHÀ solution,
increases in pH from 7 to 12 caused a gradual increase in
intensity with concomitant little red shift of the band 431
to 438 nm. This enhancement was attributed to the base
hydrolysis of lactone ring of coumarin and consequently
increased conjugation involved therein (Scheme 4). 5d
has shown selectivity only for hydroxide anion in
aqueous methanol over the other anions such as FÀ, ClÀ,
Scheme 3. Mechanism of the cyclization from 3d to 5d.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2017
Thermolysis of Chlorovinyl Imines as an Alternate Route for the Synthesis of
Pyranoquinolin-3-one and Pyranoacridin-3-one Derivatives
Scheme 4. Mechanism of fluorescence enhancement upon addition of OHÀ ion.
BrÀ, IÀ, OAcÀ, PO43À, NOÀ3 , NOÀ2 , HSO4À, and H2POÀ4 .
The change in color of chemosensor 5d (100 μM) upon
addition of hydroxyl ions (10 μM) was clearly visible
under visible light through the naked eye, whereas in the
presence of the other anions, the ligand solution was
colorless. The bright blue fluorescence under UV light
was observed only for the mixture of 5d and OHÀ in
solution (Fig. 4). This is an interesting feature by which
we can detect OHÀ without any other instrumental
techniques. In conclusion, it is evident that thermolysis of
chlorovinyl imines derivatives from various β-chloro-α,β-
unsaturated aldehyde derivatives and 6-aminocoumarin
may be an alternate route for the synthesis of the
pyranoquinolin-3-one
and
pyranoacridin-3-one
derivatives. The process saved the consumption of one
equivalent 6-aminocoumarin. The compound shows blue
fluorescence in presence of hydroxide ions under UV.
EXPERIMENTAL
Preparation of chlorovinyl imines derivatives 3(a–f):
general method.
A mixture of 6-aminocoumarin (1)
(290 mg, 1.80 mmol) and the chloroaldehyde
2
(1.80 mmol) in 35–40 mL of MeOH was stirred
vigorously at 15°C for 30 min to 1 h (reaction was
monitored by thin-layer chromatography) and then cooled
to 5–10°C. The yellow to orange solid that separated was
filtered, washed with little cold MeOH, and dried under
vacuum to obtain the chlorovinyl imines derivatives 3 in
92–96% yield. The chlorovinyl imines were directly used
for next step without further purification.
6-((E)-((E)-3-Chloro-3-phenylallylidene)amino)-2H-chromen-
2-one (3a).
Bright orange solid, yield, 92%; mp
132–133°C (EtOH); IR (KBr) νmax: 1628.8, 1729.0 cmÀ1
;
1H NMR (500 MHz, CDCl3) 6.4 (d, 1H, J = 9.6 Hz), 6.44
(d, 1H, J = 9.6 Hz), 6.98 (brs, 1H), 7.07 (m, 1H),
7.22–7.39 (m, 4H), 7.45 (d, 1H, J = 12 Hz), 7.53
(brs, 1H), 7.63 (brs, 1H), 7.9 (brs, 1H) ppm; HRMS
[electrospray ionization (ESI), 70 eV]: m/z = 310.1080
(M+ + H), 312.1128 (M+ + H + 2) [Calcd. mass for
C18H13ClNO2: 310.06 (M+ + H), 312.06 (M+ + H + 2)].
6-((E)-((E)-3-Chloro-2-methyl-3-phenylallylidene)amino)-2H-
chromen-2-one (3b).
Orange solid, yield, 92%; mp
127–128°C (EtOH); IR (KBr) νmax: 1624.0, 1733.8 cmÀ1
;
1H NMR (300 MHz, CDCl3) 2.42 (s, 3H), 6.47 (d, 1H,
J = 9.9 Hz), 7.15 (brs, 1H), 7.24 (m, 1H), 7.32 (d, 1H,
J = 8.1 Hz), 7.48 (m, 5H), 7.71 (d, 1H, J = 8.7 Hz), 8.16
(brs, 1H) ppm; HRMS (ESI, 70 eV): m/z = 323.9812
Figure 4. Fluorescence enhancement of 5d upon addition of OHÀ ion: (a)
fluorescence silent in absence of hydroxide ion and (b) bright blue fluores-
cence of 5d in presence of hydroxide ion under UV light. [Color figure
can be viewed at wileyonlinelibrary.com]
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P. Patra
Vol 000
(M+ + H), 325.9782 (M+ + H + 2) [Calcd. mass for
and dried (anhyd. Na2SO4), and solvent removed. The
crude residue thus obtained was further purified by
column chromatography (silica gel/benzene–ethyl acetate
mixture, 5:1) to furnish the pyridocoumarin derivative 5
as the only isolable product in 60–65% yield. An
analytical sample was prepared by further recrystalization
C19H15ClNO2: 324.08 (M+ + H), 326.08 (M+ + H + 2)].
(E)-6-((1-Chloro-3,4-dihydronaphthalen-2-yl)methyleneamino)-
2H-chromen-2-one (3c). Light yellow solid, yield, 94%;
mp 145–146°C (EtOH); IR (KBr) νmax
: 1631.5,
1728.4 cmÀ1 1H NMR (300 MHz, CDCl3) 2.94 (m,
;
2H), 2.96 (m, 2H), 6.47 (d, 1H, J = 9.6 Hz), 7.22–7.26
(m, 1H), 7.26–7.35 (m, 3H), 7.38 (brs, 1H), 7.43 (dd,
1H, J = 2.4 and 8.7 Hz), 7.74 (d, 1H, J = 9.6 Hz), 7.81
(dd, 1H, J = 3.6 and 5.6 Hz), 8.92 (s, 1H) ppm; 13C
NMR (75 MHz, CDCl3): 23.71, 27.37, 116.93, 117.17,
117.64, 119.25, 125.17, 126.92, 127.48, 130.04, 131.39,
132.34, 138.29, 139.09, 143.10, 143.27, 148.54, 152.46,
159.09, 160.61 ppm; HRMS (ESI, 70 eV):
m/z = 336.1084 (M+ + H), 338.1131 (M+ + H + 2)
[Calcd. mass for C20H15ClNO2: 336.08 (M+ + H),
from suitable solvent.
11-Methoxy-12,13-dihydro-3H-benzo[h]pyrano[3,2-a]acridin-
3-one (5d). Light brown solid, yield, 65%; mp 222–224°C
(CHCl3/pet. ether 60–80°C); IR (KBr) νmax: 1726.8 cmÀ1
;
1H NMR (300 MHz, CDCl3) 2.86 (m, 2H), 3.05
(brs, 2H), 3.81 (s, 3H), 6.60 (d, 1H, J = 9.8 Hz), 7.04
(d, 1H, J = 8.4 Hz), 7.31 (brt, 1H, J = 8.1 Hz), 7.63
(d, 1H, J = 9.2 Hz), 7.97 (d, 1H, J = 7.2 Hz), 8.12 (d, 1H,
J = 9.0 Hz), 8.67 (brd, 1H, J = 6.0 Hz), 8.78 (d, 1H,
J = 9.8 Hz) ppm; HRMS (ESI, 70 eV): m/z = 330.0885
(M+ + H) [Calcd. mass for C21H16NO3: 330.11 (M+ + H)].
338.08 (M+ + H + 2)].
(E)-6-((1-Chloro-5-methoxy-3,4-dihydronaphthalen-2-yl)
(mp and spectral data of the pyridocoumarins 5(a–c) and
5(e–f) are in agreement with lit. report [5]).
Compound 5a. Colorless solid, yield 65%; mp 212–
213°C (CHCl3/pet. ether 60–80°C) (lit mp 212–213°C,
methyleneamino)-2H-chromen-2-one (3d).
Light yellow
solid, yield, 95%; mp 153–154°C (EtOH); IR (KBr) νmax
:
1625.4, 1732.0 cmÀ1; H NMR (300 MHz, CDCl3) 2.53
(m, 2H), 2.88 (m, 2H), 3.71 (s, 3H), 6.40 (d, 1H,
J = 9.6 Hz), 6.80 (d, 1H, J = 7.8 Hz), 7.14–7.40 (m, 4H),
7.57 (d, 1H, J = 9.6 Hz), 7.67 (d, 1H, J = 9.6 Hz), 8.85
(s, 1H) ppm; HRMS (ESI, 70 eV): m/z = 365.9783
(M+ + H), 367.9769 (M+ + H + 2) [Calcd. mass for
1
ref of [5]).
Compound 5b. Colorless solid, yield 60%; mp 240–
242°C (CHCl3/pet. ether 60–80°C) (lit mp 240–242°C,
ref of [5]).
Compound 5c. Colorless solid, yield 64%; mp 248–
250°C (CHCl3/pet. ether 60–80°C) (lit mp 248–250°C,
C21H17ClNO3: 366.09 (M+ + H), 368.09 (M+ + H + 2)].
(E)-6-((1-Chloro-6-methoxy-3,4-dihydronaphthalen-2-yl)
ref of [5]).
methyleneamino)-2H-chromen-2-one (3e).
Yellow solid,
Compound 5e. Light yellowish solid, yield 62%; mp
yield, 95%; mp 182–184°C (EtOH); IR (KBr) νmax
:
240–242°C (CHCl3/pet. ether 60–80°C) (lit mp 240–
242°C, ref of [5]).
Compound 5f. Light yellow solid, yield 60%; mp 242–
244°C (CHCl3/pet. ether 60–80°C) (lit mp 242–244°C, ref
of [5]).
1620.0, 1731.8 cmÀ1; H NMR (300 MHz, CDCl3) 2.91
(m, 4H), 3.86 (s, 3H), 6.46 (d, 1H, J = 9.3 Hz),
6.72–6.85 (m, 3H), 7.28 (m, 2H), 7.38 (d, 1H,
J = 10.5 Hz), 7.73 (d, 1H, J = 10.2 Hz), 8.88 (s, 1H)
ppm; HRMS (ESI, 70 eV): m/z = 365.9783 (M+ + H),
1
367.9769 (M+ + H + 2) [Calcd. mass for C21H17ClNO3:
366.09 (M+ + H), 368.09 (M+ + H + 2)].
Acknowledgment. I am thankful to my supervisor Prof. Gandhi
Kumar Kar, Dean of Science, Presidency University, Kolkata,
UGC-MRP, for the financial help [fund no. PSW-79/12-13 (ERO)].
(E)-6-((7-Bromo-1-chloro-3,4-dihydronaphthalen-2-yl)
methyleneamino)-2H-chromen-2-one (3f).
Yellow solid,
yield, 96%; mp 143–144°C (EtOH); IR (KBr) νmax
:
1629.8, 1728.4 cmÀ1; H NMR (300 MHz, CDCl3) 2.50
(m, 2H), 2.79 (m, 2H), 6.50 (d, 1H, J = 9.6 Hz), 6.80
(d, 2H, J = 7.8 Hz), 6.89 (d, 1H, J = 9.3 Hz), 7.1–7.3
(m, 2H), 7.55 (s, 1H), 7.67 (d, 1H, J = 9.6 Hz), 8.89
(s, 1H) ppm; HRMS (ESI, 70 eV): m/z = 414.0125
(M+ + H), 416.0139 (M+ + H + 2) [Calcd. mass for
C20H14BrClNO2: 413.99 (M+ + H), 415.99 (M+ + H + 2)].
1
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Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2017
Thermolysis of Chlorovinyl Imines as an Alternate Route for the Synthesis of
Pyranoquinolin-3-one and Pyranoacridin-3-one Derivatives
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Journal of Heterocyclic Chemistry
DOI 10.1002/jhet