Reactivity of 3-cyano-N-ethoxycarbonyl-iminocoumarin with hydrazides as N-nucleophiles

Article abstract of DOI:10.1002/jhet.5

Condensation of 3-cyano-7-diethylamino-N-ethoxycarbonyl-iminocoumarin with various hydrazides as N-nucleophiles gave a new series of 2-oxo-2H-1- benzopyrano[2,3-d]pyrimidines bearing an acylhydrazino fragment in the 4-position. The structures of the produ

Full text of DOI:10.1002/jhet.5

28
Reactivity of 3-Cyano-N-ethoxycarbonyl-iminocoumarin with
Hydrazides as N-Nucleophiles
Vol 46
Myriam Kammoun,a Hamida Turki,a Rachid El Gharbi,a*
and Suzanne Fery-Forguesb
a
´ ´ ´ ` ´
Laboratoire de Chimie Appliquee: Heterocycles, Corps Gras et Polymeres. Faculte des Sciences
de Sfax, 3038 Sfax, Tunisia
´
5623, Universite Paul Sabatier, 31062 Toulouse Cedex, France
b
´
´
Laboratoire des Interactions Moleculaires Reactivite Chimique et Photochimique, UMR CNRS
´
*E-mail: gharbi.rachid@yahoo.fr
Received May 13, 2008
DOI 10.1002/jhet.5
Published online 4 February 2009 in Wiley InterScience (www.interscience.wiley.com).
Condensation of 3-cyano-7-diethylamino-N-ethoxycarbonyl-iminocoumarin with various hydrazides as
N-nucleophiles gave a new series of 2-oxo-2H-1-benzopyrano[2,3-d]pyrimidines bearing an acylhydra-
zino fragment in the 4-position. The structures of the products obtained were characterized using IR, H
1
NMR, 13C NMR and elemental analysis. The optical properties were reported for three of these
compounds.
J. Heterocyclic Chem., 46, 28 (2009).
INTRODUCTION
RESULTS AND DISCUSSION
Benzopyranopyrimidines have been increasingly inves-
tigated because of their important biological properties.
They exhibit for example anticancer [1,2], analgesic [3],
and antithrombotic [4] activities. In addition, benzopyra-
nopyrimidines could also be of interest because their
structure is close to that of rhodols, rhodamines, and fluo-
resceins [5], which constitute a well-known class of dyes.
Different routes have been described in the literature for
the synthesis of this class of condensed heterocycles [6–
8]. As part of our investigations on the synthesis of ben-
zopyranopyrimidines, we have reported previously [9], a
new method based on the transformation of 3-cyano-imi-
nocoumarins under the action of primary aliphatic and ar-
omatic amines, on heating in methanol. We have shown
that the reaction proceeded by an original mechanism that
involves several consecutive steps including nucleophilic
attack of the iminolactone ring, pyran ring opening, E/Z
isomerization, and subsequent cyclization. As a continua-
tion of our studies on the reactivity of 3-cyano-iminocou-
marins with N-nucleophiles, we wish to report in this ar-
ticle on the condensation of 3-cyano-7-diethylamino-N-
ethoxycarbonyl-iminocoumarin 1 with different hydra-
zides. The aim is to obtain a new series of benzopyrano-
pyrimidines incorporating an acylhydrazino fragment in
the 4-position, since the presence of this function could
improve physiological activities. The optical properties
of some benzopyranopyrimidines were also regarded.
Iminocoumarin 1 was obtained by Knoevenagel con-
densation followed by N-ethoxycarbonylation as previ-
ously described in [9]. The condensation of this com-
pound with various hydrazides (2–11, see Table 1) was
studied, first focusing on a specific system, namely 1 and
benzoic hydrazide 2 (Scheme 1), to determine the best
conditions for synthesis. The progress of the reaction was
followed by TLC analysis and by the changes in FTIR
spectra of samples taken at regular intervals from the
reaction medium. Thus, the FTIR spectra showed the pro-
gressive disappearance of the original peaks at 2214 and
1724 cmꢀ1 arising from the C¼¼N and COOEt functions,
respectively, as well as the appearance of characteristic
peaks of the pyrimidine moiety at 1632 cmꢀ1 (C¼¼N),
1664 cmꢀ1 (NHANHAC¼¼O) and 1644 cmꢀ1 (C¼¼0).
The best result was obtained by refluxing the mixture of
1 and 2 in methanol during 2 h. 4-(2-Benzoylhydrazino)-
8-diethylamino-2-oxo-2H-1-benzopyrano[2,3-d]pyrimidine
(11) was thus obtained with a yield of 92% (Scheme 1).
This product was isolated by simple filtration with high
1
purity as confirmed by H NMR, which showed the ab-
sence of resonance at 1.37 and 4.32 ppm arising from the
original ethoxy fragment, and the presence of two peaks
in the region of 10–11 ppm indicating the presence of the
NHANHACO function.
When the reaction was carried out in acetic acid at
room temperature the condensation of 1 with 2 did not
C
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2009 HeteroCorporation

January 2009
Reactivity of 3-Cyano-N-ethoxycarbonyl-iminocoumarin with
Hydrazides as N-Nucleophiles
29
Table 1
in Scheme 2 that summarizes the synthesis. The FTIR
and NMR data relative to these compounds were in
good agreement with their structure. It is interesting to
note that the presence of both amine and hydrazide
functions in hydrazide 6 could lead to the formation of
two isomers (15 and 15a) resulting from the interaction
of the imidic carbon with the two N-nucleophilic centers
in the first step of the mechanism (Scheme 3). However,
chromatographic and spectroscopic analyses showed that
the iminocoumarin was selectively converted into 15
whereas 15a was not detected, probably because the
amine function is less nucleophilic than the hydrazide
function. The structure of 15 was clearly confirmed by
Benzopyranopyrimidines obtained by condensation of iminocoumarin
(1) with various hydrazides.
Hydrazide
(RC(O)NH
NH2)
Time Yield
Benzopyranopyrimidine (h) (%)
R
2
3
11
12
13
14
15
16
17
18
19
2
3
92
63
52
87
75
48
70
45
85
4
7
1
5
1
the H NMR spectrum, which showed the presence of
ArANH2 (s, 2H, 5.71 ppm), NHANHACO (s, 1H,
10.16 ppm and s, 1H, 10.60 ppm) and the absence of
peak around 4–5 ppm related to the NH2 group of the
hydrazidic fragment.
6
2
7
8
8
16
1
OPTICAL PROPERTIES
9
CH3
The electron conjugated system of benzopyranopyri-
midines 11–19 is identical and should be poorly affected
by the nature of the R substituent. It can therefore be
expected that all these compounds share common spec-
troscopic behaviour. The optical properties were mea-
sured on three of them (namely compounds 12, 13, and
15). The results are gathered in Table 2.
Compounds 12, 13, and 15 were poorly soluble in or-
ganic solvents. All were studied in dimethylsulfoxide,
but only two of them could be dissolved in dichlorome-
thane. The solutions were filtered on paper filter prior to
spectroscopic study. However, for most of the samples,
the absorption spectrum was particularly wide, with a
markedly high baseline. This indicates that in spite of
filtration, some particles were present in solution and
scattered light.
10
3
Reaction time and yield according to the nature of substituent R.
take place and no benzopyranopyrimidine 11 was
detected. It was found that 1 reacted intramolecularly in
these conditions to produce the oxidized derivative 11a
(Scheme 1). This type of compound was reported by Bly-
thin et al. [10] when carrying out the Knoevenagel reac-
tion with salicylaldehydes and N-cyanoacety-lurethane.
On sight of these results, compound 1 was then con-
densed with hydrazides 3–10 at reflux in methanol and
the progress of the reaction was monitored by TLC. The
reagent specific structure induced changes in reactivity
and the reaction time had to be modified (Table 1).
In each case, the reaction afforded the corresponding
4-acylhydrazinobenzopyranopyrimidine 12–19 as shown
For each sample, the excitation spectrum was much
narrower than the absorption spectrum. For compound
13, both spectra had almost the same maximum. For 15
Scheme 1
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

30
M. Kammoun, H. Turki, R. E. Gharbi, and S. Fery-Forgues
Vol 46
Scheme 2. General scheme of the synthesis. Substitutent R as described in Table 1.
and 12, the excitation spectra showed a considerable
blue shift reaching 50 nm compared with the absorption
spectra. Besides, the excitation spectra did not vary with
the emission wavelength, and conversely, the emission
spectra were independent of the excitation wavelength.
This indicates the presence of only one fluorophore in
each solution. The discrepancy between the absorption
and excitation spectra could thus be attributed to the
presence of nonfluorescent impurities. But, the TLC
analyses of the three compounds gave a single spot, so
the presence of impurities could be discarded. Conse-
quently, it is most likely that these poorly soluble com-
pounds form nonfluorescent aggregates in solution, these
aggregates being particularly visible at long wavelengths
on the absorption spectra.
solvents [11,12], it appears, as could be expected, that
cyclization has led to a moderate shift of the absorption
and emission wavelengths towards longer wavelengths.
In contrast, the fluorescence lifetime is quite similar for
the two types of compounds.
CONCLUSION
This article reported the facile synthesis of new 2-
oxo-2H-1-benzopyrano[2,3-d]pyrimidines from the con-
densation of a 3-cyanoiminocoumarin with various
hydrazides. The products were easily purified and
obtained with a good yield. Their limited solubility in
most of organic solvents could be a drawback for subse-
quent applications. However, it is possible that these
compounds display interesting biological properties,
which would deserve further investigations.
The emission spectra did not show fine resolution.
Their maximum was rather close for the three com-
pounds, around 520 nm in DMSO and slightly above
500 nm in dichloromethane. A small solvent effect can
thus be noted. The lifetimes were found to be monoex-
ponential, above the nanosecond. The quantum yields
were not calculated since the absorption spectra corre-
sponded to two species at least, only one of which is
fluorescent. Therefore, the quantum yields measured
would have been lower than their actual value.
EXPERIMENTAL
7-Diethylamino-2-hydroxybenzaldehyde, malonitrile and
hydrazides were commercially available from Aldrich. All
melting points were determined on an Electrothermal 9100 ap-
paratus. Infrared spectra were registered on a Jasco FT-IR 420
spectrophotometer apparatus using KBr pellets. 1H and 13C
NMR spectra were recorded on a Bruker WP 200 spectrometer
at 300 MHz in DMSO-d6 with TMS as internal standard
(chemical shifts in ppm).
If comparing the properties of these benzopyranopyri-
midines with those of parent compound 1 in the same
Scheme 3
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January 2009
Reactivity of 3-Cyano-N-ethoxycarbonyl-iminocoumarin with
Hydrazides as N-Nucleophiles
31
Table 2
Maximum absorption wavelength (kabs), maximum excitation wavelength (kex), maximum emission wavelength (kem), and fluorescence lifetime (s)
for compounds 12, 13, and 15 in dimethylsulfoxide and dichloromethane.
Compound
kabs (nm)
kex (nm)
kem (nm)
s (ns)
12 (DMSO)
13 (DMSO)
13 (CH2Cl2)
15 (DMSO)
15 (CH2Cl2)
504
486
484 (508 sh)
508
502
458
476
480
480
451
520
518
502
520
507
2.6 ꢂ 0.3
2.9 ꢂ 0.2
3.2 ꢂ 0.2
1.5 ꢂ 0.2
1.9 ꢂ 0.2
UV/vis absorption spectra were recorded on a Hewlett-Pack-
ard 8452A diode array spectrophotometer. Steady state fluores-
cence work was performed on a Photon Technology Interna-
tional (PTI) Quanta Master 1 spectrofluorometer. All excitation
and emission spectra were corrected. Fluorescence decay was
measured with the stroboscopic technique using a Strobe Mas-
ter fluorescence lifetime spectrophotometer from PTI. The ex-
citation source was a flash lamp filled with a mixture of nitro-
gen and helium (30/70). Data were collected over 200 chan-
nels with a time-base of 0.1 ns per channel. Analysis of fluo-
rescence decay was performed using the multiexponential
method software from PTI. All spectrophotometric measure-
ments were conducted in a thermostated cell at 25ꢁC.
4-[2-(2-Thienylcarbonyl)hydrazino]-8-diethylamino-2-oxo-
2H-benzopyrano[2,3-d]pyrimidine (13). Mp: 247ꢁC. IR
(cmꢀ1): 1619 (C¼¼N), 1639 (C¼¼O), 1660 (NACOAN), 3289
1
(NH). H NMR: d ¼ 1.14 (t, J ¼ 7.0 Hz, 6H, CH3), 3.51 (q, J
¼ 7.0 Hz, 4H, CH2N), 6.76 (d, J ¼ 2.1 Hz, 1H, H9), 6.61 (s,
1H, COR), 6.89 (dd, J ¼ 9.0, 2.1 Hz, 1H, H7), 7.18 (s, 1H,
COR), 7.71 (d, J ¼ 9.0 Hz, 1H, H6), 7.80 (s, 1H, COR) , 8.46
(s, 1H, H5), 10.46 (s,1H, NH), 10.69 (s, 1H, NH). Anal. Calcd.
for C20H19N5O3S: C, 58.67; H, 4.68; N, 17.10. Found: C,
59.01; H, 4.64; N, 17.11.
4-[2-(4-Hydroxybenzoyl)hydrazino]-8-diethylamino-2-oxo-
2H-benzopyrano[2,3-d]pyrimidine (14). Mp: 270ꢁC. IR
(cmꢀ1): 1608 (C¼¼N), 1636 (C¼¼O), 1664 (NACOAN), 3326
(NH), 3423 (OH). 1H NMR: d ¼ 1.13 (t, J ¼ 6.9 Hz, 6H,
CH3), 3.50 (q, J ¼ 6.9 Hz, 4H, CH2N), 6.73 (s, 1H, H9), 6.82
(d, J ¼ 8.7 Hz, 2H, COR), 7.77 (d, J ¼ 8.7 Hz, 2H, COR),
6.85 (d, J ¼ 9.3 Hz, 1H, H7), 7.72 (d, J ¼ 9.3 Hz, 1H, H6),
8.42 (s, 1H, H5), 10.28 (s,1H, OH), 10.46 (s,1H, NH), 10.69
(s, 1H, NH). Anal. Calcd. for C22H21N5O4: C, 63.00; H, 5.05;
N, 16.70. Found: C, 62.90; H, 5.23; N, 17.71.
4-[2-(4-Aminobenzoyl)hydrazino]-8-diethylamino-2-oxo-2H-
benzopyrano[2,3-d]pyrimidine (15). Mp: 245ꢁC. IR (cmꢀ1):
1605 (C¼¼N), 1637 (C¼¼O), 1663 (NACOAN), 3210 and 3334
(NH), 3439 (NH2). 1H NMR: d ¼ 1.12 (t, J ¼ 6.9 Hz, 6H,
CH3), 3.47 (q, J ¼ 6.9 Hz, 4H, CH2N), 5.71 (s, 2H, NH2),
6.57 (d, J ¼ 8.4 Hz, 2H, COR), 6.65 (d, J ¼ 8.4 Hz, 2H,
COR), 6.69 (s, 1H, H9), 6.82 (d, J ¼ 9.3 Hz, 1H, H7), 7.67 (d,
J ¼ 9.3 Hz, 1H, H6), 8.36 (s, 1H, H5), 10.16 (s,1H, NH),
10.60 (s, 1H, NH). 13C NMR: d ¼ 12.69 (CH3), 44.84
(CH2ANH), 96.68 (C9), 105.67, 109.90 (C12, C13), 111.58
(C7), 112.77 (CHAR), 120.49 (CAR) 129.78 (C6), 131.67
(CHAR),136.96 (C5), 137.38 (CAR), 152.32 (C8), 152.93
(C4), 155.81 (C10), 156.30 (C11) 163.57 (C¼¼O), 168.09
(NHAC¼¼O). Anal. Calcd. for C22H22N6O3: C, 63.15; H, 5.30;
N, 20.08. Found: C, 62.90; H, 5.33; N, 20.00.
4-[2-(2-Furoyl)hydrazino]-8-diethylamino-2-oxo-2H-benzo-
pyrano[2,3-d]pyrimidine (16). Mp: 246ꢁC. IR (cmꢀ1): 1607
(C¼¼N), 1636 (C¼¼O), 1663 (NACOAN), 3290 (NH). 1H
NMR: d ¼ 1.13 (t, J ¼ 7.0 Hz, 6H, CH3), 3.51 (q, J ¼ 7.0
Hz, 4H, CH2N), 6.66 (m, 1H, COR), 6.76 (d, J ¼ 2.1 Hz, 1H,
H9), 6.89 (dd, J ¼ 9.0, 2.1 Hz, 1H, H7), 7.24 (d, 1H, COR),
7.76 (d, J ¼ 9.0 Hz, 1H, H6), 7.89 (m, 1H, COR), 8.46 (s, 1H,
H5), 10.15 (s,1H, NH), 10.55 (s, 1H, NH). Anal. Calcd. for
C20H19N5O4: C, 61.06; H, 4.87; N, 17.80. Found: C, 61.20; H,
4.93; N, 17.84.
3-Cyano-N-ethoxycarbonyl-7-diethylamino iminocoumarin
1. 3-Cyano-N-ethoxycarbonyl-7-diethylamino iminocoumarin 1
was prepared as previously described in [9].
General procedure for the synthesis of benzopyranopyri-
midines 11–19. A solution of 3-cyano-N-ethoxycarbonyl-7-
diethylamino iminocoumarin 1 (1.56 g, 5 mmol) and (5 mmol)
of hydrazide in 30 mL of absolute methanol was refluxed dur-
ing the time indicated in Table 1. After complete reaction, the
benzopyranopyrimidine obtained was separated by filtration
and washed with ethanol. For spectroscopic use, compound 12,
13, and 15 were purified on TLC plates using chloroform as
the eluent.
4-(2-Benzoylhydrazino)-8-diethylamino-2-oxo-2H-benzopyr-
ano[2,3-d]pyrimidine (11). Mp: 244ꢁC. IR (cmꢀ1): 1632
(C¼¼N), 1644 (C¼¼O), 1664 (NACOAN), 3331 (NH). 1H
NMR: d ¼ 1.14 (t, J ¼ 6.9 Hz, 6H, CH3), 3.51 (q, J ¼ 6.9
Hz, 4H, CH2N), 6.74 (s, 1H, H9), 6.88 (d, J ¼ 9.0, 1H, H7),
7.45–7.55 (3 H, COR), 7.75 (d, J ¼ 9.0 Hz, 1H, H6), 7.87–
7.89 (2 H, COR), 8.47 (s, 1H, H5), 10.49 (s, 1H, NH), 10.64
(s, 1H, NH). Anal. Calcd. for C22H21N5O3: C, 65.50; H, 5.25;
N, 17.36. Found: C, 65.46; H, 5.33; N, 17.35.
4-[2-(3-Fluorobenzoyl)hydrazino]-8-diethylamino-2-oxo-
2H-benzopyrano[2,3-d]pyrimidine (12). Mp: 249ꢁC. IR
(cmꢀ1): 1634 (C¼¼N, C¼¼O), 1664 (NACOAN), 3331 and
1
3335 (NH). H NMR: d ¼ 1.14 (t, J ¼ 6.9 Hz, 6H, CH3), 3.51
(q, J ¼ 6.9 Hz, 4H, CH2N), 6.75 (s, 1H, H9), 6.89 (dd, J ¼
7.2, 1.8 Hz, 1H, H7), 7.39 (m, 1H, COR), 7.53 (m, 1H, COR),
7.76 (m, 2H, COR), 7.74 (d, J ¼ 7.2, 1H, H6), 8.49 (s, 1H,
H5), 10.50 (s,1H, NH), 10.60 (s, 1H, NH). 13C NMR: d ¼
12.71 (CH3), 44.90 (CH2ANH), 96.73 (C9), 104.92, 110.00
(C12, C13), 111.80 (C7), 114.74, 118.26, 124.35, 130.63
(CHAR), 132.02 (C6), 136.76 (R), 138.04 (C5), 140.76 (C8),
153.31 (C4), 156.14 (C10), 160.52 (C11), 162.13 (CAF), 163.75
(C¼¼O), 167.95 (NHAC¼¼O). Anal. Calcd. for C22H20FN5O3:
C, 62.70; H, 4.78; N, 16.62. Found: C, 63.10; H, 4.80; N,
16.50.
4-(2-Isonicotinoylhydrazino)-8-diethylamino-2-oxo-2H-ben-
zopyrano[2,3-d]pyrimidine (17). Mp: >270ꢁC. IR (cmꢀ1):
1
1607 (C¼¼N), 1640 (C¼¼O), 1661 (NACOAN),3234 (NH). H
NMR: d ¼ 1.15 (t, J ¼ 6.9 Hz, 6H, CH3), 3.52 (q, J ¼ 6.9
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M. Kammoun, H. Turki, R. E. Gharbi, and S. Fery-Forgues
Vol 46
Hz, 4H, CH2N), 6.66 (m, 1H, COR), 6.68 (d, J ¼ 2.1 Hz, 1H,
H9), 6.89 (dd, J ¼ 7.0, 1.5 Hz, 1H, H7), 7.73 (d, 1H, COR),
7.77 (d, J ¼ 7.0 Hz, 1H, H6), 7.82 (dd, 2H, COR), 8.53 (s,
1H, H5), 10.67 (s, 2H, 2NH). Anal. Calcd. for C21H20N6O3: C,
62.37; H, 4.98; N, 20.78. Found: C, 61.97; H, 4.80; N, 20.44.
4-(2-Acetylhydrazino)-8-diethylamino-2-oxo-2H-benzopyr-
ano[2,3-d]pyrimidine (18). Mp: >270ꢁC. IR (cmꢀ1): 1609
(C¼¼N), 1636 (C¼¼O), 1662 (NACOAN),3232 (NH).1H NMR:
d ¼ 1.14 (t, J ¼ 6.9 Hz, 6H, CH3), 2.17 (s, 3H, CH3), 3.42 (q,
J ¼ 6.9 Hz, 4H, CH2N), 6.63 (d, J ¼ 2.1 Hz, 1H, H9), 6.78
(d, J ¼ 7.0, 2.1 Hz, 1H, H7), 7.50 (d, J ¼ 7.0 Hz, 1H, H6),
8.12 (s, 1H, H5), 10.73 (s, 1H, NH), 10.76 (s, 1H, NH). Anal.
Calcd. for C17H19N5O3: C, 59.81; H, 5.61; N, 20.52. Found:
C, 60.07; H, 5.63; N, 20.80.
4-[2-(2-Hydroxybenzoyl)hydrazino]-8-diethylamino-2-oxo-
2H-benzopyrano[2,3-d]pyrimidine (19). Mp: >270ꢁC. IR
(cmꢀ1): 1606 (C¼¼N), 1640 (C¼¼O), 1661 (NACOAN),3234
(NH), 3433 (OH).1H NMR: d ¼ 1.13 (t, J ¼ 6.9 Hz, 6H,
CH3), 3.51 (q, J ¼ 6.9 Hz, 4H, CH2N), 6.77 (s, J ¼ 1.5 Hz,
1H, H9), 6.90 (dd, J ¼ 7.0, 1.5 Hz, 1H, H7), 7.39 (dd, 2H,
COR), 7.75 (d, J ¼ 7.0 Hz, 1H, H6), 7.90 (d, 2H, COR), 8.53
(s, 1H, H5), 10.60 (s, 1H, 1NH), 10.75 (s, 1H, OH), 10.90 (s,
1H, NH). Anal. Calcd. for C22H21N5O4: C, 63.00; H, 5.05; N,
16.70. Found: C, 62.61; H, 5.42, N, 16.57.
NMR: d ¼ 12.86 (CH3), 45.29 (CH2ANH), 96.97 (C9),
104.98, 110.31 (C12, C13), 112.49 (C7), 133.41 (C6), 144.38
(C5), 154.89 (C8), 157.34 (C4), 157.57 (C10), 162.52 (C¼¼O),
168.57 (C¼¼O). Anal. Calcd. for C15H15N3O3: C, 63.15; H,
5.30; N, 14.73. Found: C, 62.96; H, 5.21; N, 14.69.
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of 1 and (0.68 g, 5 mmol) of benzoic hydrazide 2 were stirred
at 20ꢁC in 20 mL of glacial acetic acid for 20 h. The product
was isolated by filtration and recrystallized in dimethylsulfox-
ide. Mp 250ꢁC. Yield: 55%. IR (cmꢀ1): 1641 (C¼¼O), 3246
(NH). 1H NMR (300 MHz, DMSO-d6): d ¼ 1.14 (t, J ¼ 6.9
Hz, 6H, CH3), 3.53 (q, J ¼ 6.9Hz, 4H, CH2N), 6.80 (d, J ¼
1.5 Hz, 1H, H9), 6.89 (dd, J ¼ 6.9, 1.5 Hz, 1H, H7), 7.74 (d, J
¼ 6.9 Hz, 1H, H6), 8.59 (s, 1H, H5), 11.06 (s,1H, NH). 13C
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Journal of Heterocyclic Chemistry
DOI 10.1002/jhet