Novel chromeno[2,3-b]pyridines from Basic Rearrangement of 4-Oxo-chromene-3-carbonitrile

Article abstract of DOI:10.1080/00397910902788141

A new series of 2,3-disubstituted-5-oxochromeno[2,3-b]pyridine derivatives has been obtained throughout a 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)-catalyzed reaction of 4-oxo-4H-chromene-3-carbonitrile with various active methyl and methylene compounds. T

Full text of DOI:10.1080/00397910902788141

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Novel Chromeno[2,3-
b]pyridines from Basic
Rearrangement of 4-Oxo-
chromene-3-carbonitrile
Magdy A. Ibrahim a
a Department of Chemistry, Faculty of Education,
Ain Shams University, Cairo, Egypt
Version of record first published: 04 Sep 2009
To cite this article: Magdy A. Ibrahim (2009): Novel Chromeno[2,3-b]pyridines from
Basic Rearrangement of 4-Oxo-chromene-3-carbonitrile, Synthetic Communications:
An International Journal for Rapid Communication of Synthetic Organic Chemistry,
39:19, 3527-3545
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Synthetic Communications1, 39: 3527–3545, 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910902788141
Novel Chromeno[2,3-b]pyridines from
Basic Rearrangement of 4-Oxo-chromene-
3-carbonitrile
Magdy A. Ibrahim
Department of Chemistry, Faculty of Education,
Ain Shams University, Cairo, Egypt
Abstract: A new series of 2,3-disubstituted-5-oxochromeno[2,3-b]pyridine deriva-
tives has been obtained throughout a 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)-
catalyzed reaction of 4-oxo-4H-chromene-3-carbonitrile with various active
methyl and methylene compounds. The Friedla¨nder reaction of 2-amino-4-
oxo-4H-chromene-3-carboxaldehyde with the same active methyl and methy-
lene compounds led to the identical products, suggesting that basic catalyzed
ring rearrangement took place during the course of reaction.
Keywords: Basic rearrangement, chromeno[2,3-b]pyridine, Friedla¨nder, heteroan-
nulated chromone, 4-oxo-4H-chromene-3-carbonitrile
INTRODUCTION
The 4-oxo-4H-chromene (chromone) moiety is an integral part of many
natural products.[1–5] Derivatives of 4-oxo-4H-chromene also drew much
attention because of its activity against the human immunodeficiency virus
(HIV-1)[6–8] that causes acquired immunodeficiency syndrome (AIDS) and
its broad anti-inflammatory,[9] antitumor,[10,11] antibacterial,[11] antimicrobial,[12]
antifungal,[13,14] antibiotic,[15] and insecticidal activities.[16] Heteroannulated
chromones showed important pharmacological,[17] anti-inflammatory,
Received September 24, 2008.
Address correspondence to Magdy A. Ibrahim, Department of Chemistry,
Faculty of Education, Ain Shams University, Roxy 11711, Cairo, Egypt. E-mail:
magdy_ahmed1977@yahoo.com
3527

3528
M. A. Ibrahim
and antiplatelet activities.[18] It was reported that[19] condensation reaction
of 2-amino-4-oxo-4H-chromene-3-carboxaldehyde with some active
methylene compounds afforded 2,3-disubstituted chromeno[2,3-b]pyri-
dines. It is expected the presence of heterocyclic rings in the 2-position
may render chromenopyridines more potent and biologically activity, like
flavone.[20–23] The present work describes the synthesis of some new het-
eroannulated chromones starting from 4-oxo-4H-chromene-3-carboni-
trile (1) with some active methyl and methylene compounds in the
presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a basic catalyst.
RESULTS AND DISCUSSION
Condensation reaction of 4-oxo-4H-chromene-3-carbonitrile (1) with
2-acetylthiophene, 3-acetylpyridine, 5-acetyl-4-hydroxy-2H-1,3-thiazine-
2,6(3H)-dione, or 3-acetyl-4-hydroxy-6-methyl-2H-pyran-2-one in abso-
lute ethanol and few drops of DBU as a basic catalyst afforded
2-heteroaryl-5-oxo-5H-chromeno[2,3-b]pyridines (2a–d). Compounds
2a–d were obtained by the classical Friedla¨nder condensation of
2-amino-4-oxo-4H-chromene-3-carboxaldehyde (3) with the same acetyl
derivatives and under the same conditions (Scheme 1). Formation of
Scheme 1. Formation of chromeno[2,3-b]pyridines 2a–d.

Novel Chromeno[2,3-b]pyridines
3529
compounds 2a–d was accomplished via a tandem cyclization reaction
through Michael addition of the active methyl ketones to the c-pyrone
moiety of compound 1, followed by basic rearrangement of c-pyrone
ring, giving rise to 3-vinyl-2-aminochromone intermediates, which
undergo cyclocondensation to furnish chromenopyridines (Scheme 1).
Also, condensation of carbonitrile 1 with 4,6-diacetylresorcinol was
studied with a different molar ratio. Thus, treatment of 1 with 4,6-
diacetylresorcinol in 1:1 and 2:1 molar ratio gave compounds 4 and 5,
respectively. 4,6-Bis(5-oxo-5H-chromeno[2,3-b]pyridin-2-yl) resorcinol
(5) was obtained authentically from the interaction of 4 with carbonitrile
1 in absolute ethanol containing a few drops of DBU. Formylation of
compound 4 using Vilsemier-Haack conditions afforded 4-oxo-4H-
chromene-3-carboxaldehyde derivative 7. Alternatively, compound 7
was obtained authentically from the basic rearrangement of carbonitrile
1 using 6-acetyl-7-hydroxy-4-oxo-4H-chromene-3-carboxaldehyde (6)
(Scheme 2). Infrared (IR) spectrum of compound 7 showed absorption
bands at 3403, 1721, 1698, and 1661 assigned to (OH), (C¼O aldehyde),
and (2 C¼O), respectively. Its 1H NMR spectrum exhibited characteristic
Scheme 2. Formation of chromeno[2,3-b]pyridines 4, 5, and 7.

3530
M. A. Ibrahim
signals at d 8.84, 10.02, and 12.64 for H-2, CHO, and OH protons,
respectively.
Some new 2,3-disubstituted-5-oxo-5H-chromeno[2,3-b]pyridines 8a–c
were synthesized by condensation of 1 with a variety of active methylene
compounds. Therefore, refluxing of carbonitrile 1 with deoxybenzoin,
dibenzoylmethane, and ethyl benzoylacetate in boiling ethanol containing
DBU gave 2-phenyl-3-substituted-5-oxo-5H-chromeno[2,3-b]pyridines
1
8a–c (Scheme 3). H NMR spectra showed singlet signals at the range d
8.29–8.97 for the H-4 protons.
Scheme 3. Reaction of carbonitrile 1 with acyclic active methylene compounds.

Novel Chromeno[2,3-b]pyridines
3531
Theoretically, the unsymmetrical ketone such as acetoacetanilide has
two possible cyclization pathways, giving rise to two regioisomers
depending on whether the a-methyl or a-methylene group undergoes ring
opening of the c-pyrone ring of compound 1.[24,25] Herein, DBU-
catalyzed condensation of acetoacetanilide with compound 1 yielded
only 2-methyl-5-oxo-N-phenyl-5H-chromeno[2,3-b]pyridine-3-carboxa-
mide (9). The other possible product namely 2-(5-oxo-5H-chromeno
[2,3-b]pyridin-2-yl)-N-phenylacetamide (10), was not obtained (Scheme 3).
1
This conclusion was based upon the H NMR spectrum of compound 9
(in particular, the two singlets at d 2.07 and 8.62 assigned to CH3 and
H-4, respectively, and the absence of CH2 signal).
On the other hand, various 2-amino-5-oxo-5H-chromeno[2,3-b]
pyridines 11a–e bearing different substituents at 3-position were synthe-
sized. Thus, condensation of carbonitrile 1 with phenylacetonitrile and
phenylthioacetonitrile, in the presence of DBU as a catalyst, afforded
the amines 11a and 11b, respectively. The ethyl ester 11c was obtained
from treatment of the carbonitrile 1 with ethyl cyanoacetate, in ethanol
containing DBU, while the corresponding methyl ester 11d was isolated
when sodium methoxide was used as a catalyst (Scheme 3). The forma-
tion of the methyl ester 11d instead of the expected ethyl ester 11c, in
the course of the last reaction, was due to selective ester-exchange of
ethoxide ion by methoxide ion.[26] Also, reaction of 1 with N0-[(4-chlorophenyl)
methylene]-2-cyanoacetohydrazide yielded the carbohydrazide 11e. Compound
11e was also obtained authentically from the condensation of ethyl ester
11c with 4-chlorobenzaldehyde hydrazone in absolute ethanol (Scheme 3).
Analytical and spectroscopic data fully support the structure assignment
for compounds 11a–e. 1H NMR spectra revealed the presence of
singlet signals in the region d 8.18–8.73 assigned to H-4 protons of the
pyridine rings.
Treatment of
1
with 2-cyano-N0-[(chromon-3-yl)methylene]
acetohydrazide (12) in ethanol=DBU did not give the expected product
13 but gave the ethyl ester 11c. Surprisingly, when the reaction took place
in methanol instead of ethanol, the methyl ester 11d was obtained.
Formation of esters 11c and 11d from 1 in alcohol may be explained
through the formation of carbohydrazide 13 followed by c-pyrone ring
opening to produce the N-acylpyrazole derivative 14, which is susceptible
to replacement of the pyrazolyl ring by the alcohol present in the
medium, which then gave the corresponding esters 11c and 11d
(Scheme 4). Also, reaction of 1 with 3-(3,5-dimethyl-1H-pyrazol-1-yl)-3-
oxopropanenitrile (15) under same reaction conditions in ethanol gave
the ethyl ester 11c. Replacing ethanol with methanol gave the methyl
ester 11d (Scheme 4). These results fortified the hypothesized formation
of N-acylpyrazole intermediate 14 in the former reaction. Therefore, it

3532
M. A. Ibrahim
Scheme 4. Reaction of carbonitrile 1 with N-cyanoacetyl derivatives.
can be concluded that the reaction of 4-oxo-4H-chromene-3-carbonitrile
(1) with N-cyanoacetylpyrazoles is alcohol dependent.
Interestingly, cyclic a-methylene ketones and cyclic 1,3-diketones also
undergo smooth and efficient ring opening and ring closure (RORC)[27] for
compound 1, yielding heteroannulated 4-oxo-4H-chromene derivatives.
Thus, reaction of 1 with cyclopentanone (17), 2-phenyliminothiazolidin-4-
one (18), pyrazoline-3,5-dione (19), 5,5-dimethylcyclo-hexane-1,3-dione
(20), and barbituric and thiobarbituric acids (21a and 21b) afforded a
new series of tetracyclic systems 22–26, respectively (Scheme 5). The novel
polyfused systems 22–26 showed the pyridine ring protons as singlets in the
1
region d 8.17–8.85 in their H NMR spectra.
Finally, the reaction of 1 with hippuric acid in acetic anhydride
yielded compound 29 via the intermediates 27 and 28. Refluxing

Novel Chromeno[2,3-b]pyridines
3533
Scheme 5. Reaction of carbonitrile 1 with cyclic active methylene compounds.
compound 1 with hippuric acid in acetic anhydride in the presence of
freshly fused sodium acetate afforded the tetracyclic system 31
(Scheme 6).
CONCLUSIONS
In conclusion, a new series of 2,3-disubstituted-5-oxochromeno[2,3-b]-
pyridines and related heterocyclic systems are conveniently prepared

3534
M. A. Ibrahim
Scheme 6. Reaction of carbonitrile 1 with hippuric acid.
starting from 4-oxo-4H-chromene-3-carbonitrile and some active methyl
or methylene compounds in the presence of DBU.
EXPERIMENTAL
Melting points are uncorrected and were recorded in open capillary tubes
on a Stuart SMP3 melting-point apparatus. IR spectra were recorded on
Fourier transform (FT)-IR Bruker Vector 22 spectrophotometer using
1
the KBr wafer technique. H NMR spectra (chemical shift in d) were
measured on a Gemini 200-MHz spectrometer using dimethylsulfoxide
(DMSO)-d6 as solvent and tetramethysilane (TMS) as an internal

Novel Chromeno[2,3-b]pyridines
3535
standard. Mass spectra (MS) were obtained using gas chromatography
GC-MS-QP 1000 ex Shimadzu mass spectrometer (70eV). Elemental
microanalyses were performed at the Cairo University Microanalytical
Center. 4-oxo-4H-chromene-3-carbonitrile (1),[19] 2-amino-4-oxo-4H-
chromene-3-carboxaldehyde (3),[19] 5-acetyl-4-hydroxy-2H-1,3-thiazine-2,6
(3H)-dione,[28] 4,6-diacetylresorcinol,[29] 2-cyano-N0-[(4-oxo-4H-chromen-
3-yl)methylene] acetohydrazide (12),[30] and 1-cyanoacetyl-3,5-
dimethylpyrazole (15)[31] were prepared according to literature methods.
2-Heteroaryl-5-oxo-5H-chromeno[2,3-b]pyridines (2a–d)
A mixture of 4-oxo-4H-chromene-3-carbonitrile (1) (0.513 g, 3 mmol)
(method A) or 2-amino-4-oxo-4H-chromene-3-carboxaldehyde (3)
(0.567 g, 3 mmol) (method B) and the appropriate acetyl heterocycles
(namely, 2-acetylthiophene, 3-acetylpyridine, 5-acetyl-4-hydroxy-2H-
1,3-thiazine-2,6(3H)-dione, or 3-acetyl-4-hydroxy-6-methyl-2H-pyran-2-
one) (3 mmol) in absolute ethanol (20 mL) and DBU (0.1 mL) was
refluxed for 1 h. The solid obtained during heating was filtered and
recrystallized from the appropriate solvent to give 2a–d. Compound 2a,
crystallized from DMF=EtOH, mp 256ꢀC, yield 45% (method A), 32%
(method B): IR (KBr, cmꢁ1): 3021 (CHarom.), 1660 (C¼Opyrone), 1616
1
(C¼N). H NMR (DMSO, d): 6.45 (t, 1H, H-30), 6.82–7.66 (m, 5H,
Ar-H), 8.02 (d, 1H, H-6), 8.41 (d, 1H, H-3), 8.76 (d, 1H, H-4). M=z (I
%): 279 (15), 237 (24), 127 (15), 120 (27), 92 (42), 84 (58), 58 (18), 65
(30), 56 (100). Anal. calcd. for C16H9NO2S (279.32): C, 68.80; H, 3.25;
N, 5.01; S, 11.48. Found: C, 68.75; H, 3.21; N, 4.89; S, 11.42. Compound
2b, crystallized from DMF, mp > 320ꢀC, yield 45% (method A), 33%
(method B): IR (KBr, cmꢁ1): 3051 (CHarom.), 1673 (C¼Opyrone), 1597
(C¼N). M=z (I %): 274 (53), 168 (31), 120 (13), 104 (11), 92 (38), 78
(100), 65 (34). Anal. calcd. for C17H10N2O2 (274.28): C, 74.45; H, 3.67;
N, 10.21. Found: C, 74.30; H, 3.82; N, 10.14. Compound 2c, crystallized
from DMF, mp 276ꢀC, yield 38% (method A), 27% (method B). IR (KBr,
cmꢁ1): 3380 (OH), 3196 (NH), 3062 (CHarom.), 1680 (2 C¼O), 1660
(C¼Opyrone), 1601 (C¼N). 1H NMR (DMSO, d): 7.51 (t, 1H, H-7),
7.71 (d, 1H, H-9), 7.91 (t, 1H, H-8), 8.16 (d, 1H, H-6), 8.55 (d, 1H,
H-3), 8.80 (d, 1H, H-4), 9.17 (s, 1H, NH). Anal. calcd. for C16H8N2O5S
(340.32): C, 56.47; H, 2.37; N, 8.23; S, 9.42. Found: C, 56.18; H, 2.23; N,
8.21; S, 9.35. Compound 2d, crystallized from EtOH, mp 101ꢀC, yield
42% (method A), 33% (method B). IR (KBr, cmꢁ1): 3420 (OH), 3083
(CHarom.), 2927, 2854 (CH3), 1710 (OC¼O), 1657 (C¼Opyrone), 1615
1
(C¼N). H NMR (DMSO, d): 2.18 (s, 3H, CH3), 7.58–8.16 (m, 5H,
Ar-H), 8.75 (d, 1H, H-4), 9.15 (s, 1H, Ar-Ha-pyrone), 13.67 (bs, 1H,

3536
M. A. Ibrahim
OH). Anal. calcd. for C18H11NO5 (321.29): C, 67.29; H, 3.45; N, 4.36.
Found: C, 66.99; H, 3.41; N, 4.20.
2-(5-Acetyl-2,4-dihydroxyphenyl)-5-oxo-5H-chromeno[2,3-b]pyridine (4)
A mixture of 1 (0.513 g, 3 mmol) and 4,6-diacetylresorcinol (0.582 g,
3 mmol) in absolute ethanol (20 mL) and DBU (0.1 mL) was refluxed
for 1 h. The yellow crystals obtained after cooling were filtered and
recrystallized from DMF to give 4, mp 308ꢀC, yield 30%. IR
(KBr, cmꢁ1): 3421 (2 OH), 3052 (CHarom.), 2923, 2854 (CH3), 1671
1
(C¼Oacetyl), 1657 (C¼Opyrone), 1599 (C¼N). H NMR (DMSO, d): 2.68
(s, 3H, CH3), 6.41 (s, 1H, H-30), 7.02 (s, 1H, H-60), 7.54–8.19 (m, 3H,
Ar-H), 8.35 (d, 1H, H-6), 8.59 (d, 1H, H-3), 9.05 (d, 1H, H-4), 12.40
(bs, 2H, 2 OH). M=z (I %): 347 (39), 332 (100), 196 (8), 167 (5), 151
(10), 128 (11), 120 (23), 109 (6), 105 (25), 92 (71), 63 (82). Anal. calcd.
for C20H13NO5 (347.33): C, 69.16; H, 3.77; N, 4.03. Found: C, 68.94;
H, 3.69; N, 4.00.
4,6-Bis(5-oxo-5H-chromeno[2,3-b]pyridin-2-yl)resorcinol (5)
Method A
A mixture of 1 (1.026 g, 6 mmol) and 4,6-diacetylresorcinol (0.582 g,
3 mmol) in absolute ethanol (30 mL) and DBU (0.2 mL) was refluxed
for 1 h. The yellow crystals obtained during heating were filtered and
crystallized from DMSO to give 5, mp > 320ꢀC, yield 29%.
Method B
A mixture of 4 (0.347 g, 1 mmol) and 4-oxo-4H-chromene-3-carbonitrile
(1) (0.171 g, 1 mmol) in absolute ethanol (20 mL) and DBU (0.1 mL)
was refluxed for 1 h. The yellow crystals obtained during heating were fil-
tered and crystallized from DMSO to give 5, mp > 320ꢀC, yield 25%. IR
(KBr, cmꢁ1): 3422 (2 OH), 3064 (CHarom.), 1656 (C¼Opyrone), 1598
1
(C¼N). H NMR (DMSO, d): 6.37 (s, 1H, H-20), 7.08 (s, 1H, H-50),
7.60–8.86 (m, 12H, Ar-H), 9.82 (bs, 2H, 2 OH). Anal. calcd. for
C30H16N2O6 (500.47): C, 72.00; H, 3.22; N, 5.60. Found: C, 71.84; H,
3.13; N, 5.51.

Novel Chromeno[2,3-b]pyridines
3537
7-Hydroxy-4-oxo-6-(5-oxo-5H-chromeno[2,3-b]pyridin-2-yl)-4H-
benzopyran-3-carboxaldehyde (7)
Method A
Phosphoryl chloride (3 mL) was added dropwise to precooled DMF
(10 mL), and the mixture was stirred at room temperature for 30 min.
A solution of 4 (0.385 g, 1 mmol) in DMF (5 mL) was added dropwise
at room temperature during 15 min. The mixture was stirred at 60ꢀC
for 2 h, left overnight, and poured onto crushed ice (30 g). The solid
obtained was filtered and crystallized from DMF=H2O to give 7,
mp > 320ꢀC, yield 41%.
Method B
A mixture of 1 (0.171 g, 1 mmol) and 6-acetyl-7-hydroxy-4-oxo-4H-
chromene-3-carboxaldehyde (6) (0.232 g, 1 mmol) in absolute ethanol
(20 mL) and DBU (0.1 mL) was refluxed for 1 h. The solid obtained after
cooling was filtered and crystallized from DMF=H2O to give
7, mp > 320ꢀC, yield 34%. IR (KBr, cmꢁ1): 3403 (OH), 3058 (CHarom.),
2780 (CHald.), 1721 (C¼Oald.), 1698 (C¼Opyrone), 1661 (C¼Opyrone),
1607 (C¼N). 1H NMR (DMSO, d): 6.39 (s, 1H, H-8), 7.11–7.95
(m, 3H, Ar-H), 8.17 (d, 1H, H-60), 8.49 (s, 1H, H-5), 8.59 (d, 1H,
H-30), 8.66 (d, 1H, H-40), 8.84 (s, 1H, H-2), 10.02 (s, 1H, CHO), 12.64
(bs, 1H, OH). Anal. calcd. for C22H11NO6 (385.34): C, 68.58; H, 2.88;
N, 3.63. Found: C, 68.45; H, 2.71; N, 3.38.
3-Substituted-2-phenyl-5-oxo-5H-chromeno[2,3-b]pyridines (8a–c)
A mixture of 1 (0.513 g, 3 mmol) and a-methylene ketones (namely, deox-
ybenzoin, dibenzoylmethane, and ethyl benzoylacetate) (3 mmol) in abso-
lute ethanol (20 mL) and DBU (0.1 mL) was refluxed for 30 min. The
solid obtained after cooling was filtered and crystallized to give 8a–c.
Compound 8a, crystallized from EtOH, mp 222ꢀC, yield 22%. IR
1
(KBr, cmꢁ1): 3045 (CHarom.), 1663 (C¼Opyrone), 1602 (C¼N). H NMR
(DMSO, d): 7.20–7.91 (m, 13H, Ar-H), 8.13 (d, 1H, H-6), 8.29 (s, 1H,
H-4). Anal. calcd. for C24H15NO2 (349.39): C, 82.51; H, 4.33; N, 4.01.
Found: C, 82.32; H, 4.23; N, 3.95. Compound 8b, crystallized from
MeOH, mp 245ꢀC, yield 39%. IR (KBr, cmꢁ1): 3071 (CHarom.), 1698
(C¼Obenzoyl), 1659 (C¼Opyrone), 1598 (C¼N). 1H NMR (DMSO, d):
7.20–8.19 (m, 13H, Ar-H), 8.51 (d, 1H, H-6), 8.97 (s, 1H, H-4). M=z

3538
M. A. Ibrahim
(I %): 377 (2), 237 (11), 161 (100), 133 (11), 121 (79), 120 (34), 105 (12), 94
(21), 92 (78), 77 (34), 65 (43). Anal. calcd. for C25H15NO3 (377.40): C,
79.56; H, 4.01; N, 3.71. Found:C, 79.51; H, 4.00; N, 3.70. Compound
8c, crystallized from DMF=EtOH, mp 270ꢀC, yield 41%. IR (KBr, cmꢁ1):
3065 (CHarom.), 2977, 2923, 2895 (CH2, CH3), 1734 (C¼Oester), 1667
(C¼Opyrone), 1607 (C¼N). 1H NMR (DMSO, d): 1.37 (t, 3H, CH3),
4.30 (q, 2H, CH2), 7.33–8.12 (m, 8H Ar-H), 8.35 (d, 1H, H-6), 8.50 (s,
1H, H-4). Anal. calcd. for C21H15NO4 (345.36): C, 73.04; H, 4.38; N,
4.06. Found: C, 73.00; H, 4.32; N, 4.01.
2-Methyl-5-oxo-N-phenyl-5H-chromeno[2,3-b]pyridine-3-carboxamide (9)
A mixture of 1 (0.513 g, 3 mmol) and acetoacetanilide (0.536 g, 3 mmol) in
absolute ethanol (20 mL) and DBU (0.1 mL) was refluxed for 30 min. The
yellow crystals obtained after cooling were filtered and recrystallized
from DMF=EtOH to give 9, mp 270–271ꢀC, yield 34%. IR (KBr, cmꢁ1):
3287 (NH), 3069 (CHarom.), 2924, 2853 (CH3), 1671 (C¼Oamide), 1646
(C¼Opyrone), 1598 (C¼N). 1H NMR (DMSO, d): 2.07 (s, 3H, CH3),
7.28–7.74 (m, 8H Ar-H), 8.24 (d, 1H, H-6), 8.62 (s, 1H, H-4), 11.64 (bs,
1H, NH). M=z (I %): 330 (5), 238 (55), 210 (15), 155 (11), 127 (17), 120
(6), 104 (5), 92 (58), 65 (100). Anal. calcd. for C20H14N2O3 (330.35): C,
72.72; H, 4.27; N, 8.48. Found: C, 72.59; H, 4.18; N, 8.36.
2-Amino-3-(phenyl/phenylthio)-5-oxo-5H-chromeno[2,3-b]pyridines (11a, b)
A mixture of 1 (0.513g, 3 mmol) and phenyl=phenylthioacetonitriles
(3mmol) in absolute ethanol (20 mL) and DBU (0.1 mL) was refluxed
for 30min. The yellow crystals obtained after cooling were filtered and
crystallized to give 11a and 11b. Compound 11a, crystallized from EtOH,
mp 241–242ꢀC, yield 40%. IR (KBr, cmꢁ1): 3447, 3239 (NH2), 3025
1
(CHarom.), 1660 (C¼Opyrone), 1615 (C¼N). H NMR (DMSO, d): 7.58
(bs, 2H, NH2), 7.79–8.15 (m, 9H, Ar-H), 8.18 (s, 1H, H-4). M=z (I %):
288 (24), 210 (13), 181 (9), 161 (51), 120 (73), 92 (83), 65 (100). Anal. calcd.
for C18H12N2O2 (288.31): C, 74.99; H, 4.20; N, 9.72. Found: C, 74.87; H,
4.05; N, 9.65. Compound 11b, crystallized from EtOH, mp 220–221ꢀC,
yield 32%. IR (KBr, cmꢁ1): 3386, 3297 (NH2), 3075 (CHarom.), 1640
(C¼Opyrone), 1612 (C¼N). 1H NMR (DMSO, d): 7.20–7.49 (m, 7H,
Ar-H), 7.59 (d, 2H, NH2), 7.81 (d, 1H, H-8), 8.08 (d, 1H, H-6), 8.31
(s, 1H, H-4). Anal. calcd. for C18H12N2O2S (320.37): C, 67.48; H, 3.78;
N, 8.74; S, 10.01. Found: C, 67.67; H, 3.98; N, 8.71; S, 10.13.

Novel Chromeno[2,3-b]pyridines
3539
Ethyl 2-Amino-5-oxo-5H-chromeno[2,3-b]pyridine-3-carboxylate (11c)
Method A
A mixture of 1 (0.513 g, 3 mmol) and ethyl cyanoacetate (0.339 g, 3 mmol)
in absolute ethanol (20 mL) and DBU (0.1 mL) was refluxed for 30 min.
The white crystals obtained during heating were filtered and recrystal-
lized from DMF=EtOH, to give 11c, mp 239–240ꢀC, yield 47%.
Method B
A mixture of 1 (0.513g, 3 mmol) and 2-cyano-N0-[4-oxo-4H-chromen-2-yl)
methylene]acetohydrazide (12) or 1-cyanoacetyl-3,5-dimethylpyrazole (15)
(3 mmol) in absolute ethanol (20 mL) and DBU (0.1 mL) was refluxed for
30 min. The white crystals obtained during heating were filtered and
recrystallized from DMF=EtOH to give 11c, mp 239–240ꢀC, yield 36%.
IR (KBr, cmꢁ1): 3398, 3284 (NH2), 3080 (CHarom.), 2986, 2934, 2904
(CH2, CH3), 1698 (C¼Oester), 1662 (C¼Opyrone), 1604 (C¼N). 1H
NMR (DMSO, d): 1.35 (t, 3H, CH3), 4.32 (q, 2H, CH2), 7.43 (t, 1H,
H-7), 7.55 (d, 1H, H-9), 7.80 (t, 1H, H-8), 8.04 (d, 1H, H-6), 8.37 (bs,
2H, NH2), 8.73 (s, 1H, H-4). Anal. calcd. for C15H12N2O4 (284.27): C,
63.38; H, 4.25; N, 9.85. Found: C, 63.37; H, 4.24; N, 9.64.
Methyl 2-Amino-5-oxo-5H-chromeno[2,3-b]pyridine-3-carboxylate (11d)
Method A
A mixture of 1 (0.513 g, 3 mmol) and ethyl cyanoacetate (0.339 g, 3 mmol)
in sodium methoxide (prepared by dissolving 0.1 g sodium in 20 mL
methanol) was refluxed for 30 min. After cooling, the reaction mixture
was neutralized with 10% acetic acid. The white crystals obtained
were filtered and recrystallized from DMF=H2O to give 11d, mp
269ꢀC, yield 49%.
Method B
A mixture of 1 (0.513g, 3 mmol) and 2-cyano-N0-[4-oxo-4H-chromen-2-yl)
methylene]acetohydrazide (12) or 1-cyanoacetyl-3,5-dimethylpyrazole (15)
(3 mmol) in methanol (20 mL) and DBU (0.1mL) was refluxed for 30min.
The white crystals obtained during heating were filtered and recrystallized

3540
M. A. Ibrahim
from DMF=H2O to give 11d, mp 269ꢀC, yield 37%. IR (KBr, cmꢁ1):
3341, 3261 (NH2), 3075 (CHarom), 2975, 2932 (CH3), 1694 (C¼Oester),
1663 (C¼Opyrone), 1610 (C¼N). 1H NMR (DMSO, d): 3.73 (s, 3H,
CH3), 7.40 (t, 1H, H-7), 7.51 (d, 1H, H-9), 7.65 (t, 1H, H-8), 8.16 (bs,
2H, NH2), 8.36 (d, 1H, H-6), 8.69 (s, 1H, H-4). M=z (I %): 270 (37),
239 (29), 211 (23), 181 (15), 127 (17), 121 (32), 104 (14), 92 (55), 63
(100). Anal. calcd. for C14H10N2O4 (270.25): C, 62.22; H, 3.73; N,
10.37. Found: C, 62.18; H, 3.70; N, 10.25.
2-Amino-N0-[(4-chlorophenyl)methylene]-5-oxo-5H-chromeno
[2,3-b]pyridine-3-carbohydrazide (11e)
Method A
A mixture of 1 (0.513 g, 3 mmol) and N0-[(4-chlorophenyl)methylene]-2-
cyanoacetohydrazide (0.662 g, 3 mmol) in absolute ethanol (20 mL) and
DBU (0.1 mL) was refluxed for 30 min. The solid obtained during heating
was filtered and recrystallized from DMF to give 11e, mp > 320ꢀC,
yield 55%.
Method B
A mixture of 11c (0.852 g, 3 mmol) and 4-chlorobenzaldehyde hydrazone
(0.463 g, 3 mmol) in absolute ethanol was refluxed for 2 h. The solid
obtained during heating was filtered and recrystallized from DMF to give
11e, mp > 320ꢀC, yield 42%. IR (KBr, cmꢁ1): 3357, 3234 (NH2), 3135
1
(NH), 3063 (CHarom.), 1667 (C¼Opyrone), 1627 (C¼Oamide). H NMR
(DMSO, d): 7.16–8.04 (m, 9H, Ar-H and NH2), 8.13 (s, 1H, CH¼N),
8.35 (d, 1H, H-6), 8.64 (s, 1H, H-4), 11.57 (s, 1H, NH). Anal. calcd.
for C20H13ClN4O3 (392.80): C, 61.16; H, 3.34; N, 14.26. Found: C,
61.05; H, 3.26; N, 14.21.
Cyclopenta[b]chromeno[3,2-e]pyridin-5-one (22)
A mixture of 1 (0.513 g, 3 mmol) and cyclopentanone (17) (0.711 g,
3 mmol) in absolute ethanol (20 mL) and DBU (0.1 mL) was refluxed
for 15 min. The solid obtained during heating was filtered and recrystal-
lized from dioxane to give 22, mp 241–242ꢀC, yield 59%. IR (KBr, cmꢁ1):
1
3092 (CHarom.), 2928, 2894 (CH2), 1668 (C¼Opyrone), 1616 (C¼N). H
NMR (DMSO, d): 2.01 (m, 2H, CH2), 2.84 (t, 2H, CH2), 3.12 (t, 2H,

Novel Chromeno[2,3-b]pyridines
3541
CH2), 7.35 (t, 1H, H-7), 7.51 (d, 1H, H-9), 7.62 (t, 1H, H-8), 7.98 (d, 1H,
H-6), 8.53 (s, 1H, H-4). Anal. calcd. for C15H11NO2 (237.26): C, 75.94; H,
4.67; N, 5.90. Found: C, 75.92; H, 4.62; N, 5.82.
2-Anilino-chromeno[2,3-b][1,3]thiazolo[5,4-e]pyridin-10-one (23)
A mixture of 1 (0.513 g, 3 mmol) and 2-(phenylimino)-1,3-thiazolidin-4-
one (18) (1.035 g, 3 mmol) in absolute ethanol (20 mL) and DBU
(0.1 mL) was refluxed for 15 min. The solid obtained during heating
was filtered and recrystallized from DMF to give 23, mp > 320ꢀC, yield
26%. IR (KBr, cmꢁ1): 3422 (NH), 3070 (CHarom.), 1660 C¼Opyrone),
1615 (C¼N). 1H NMR (DMSO, d): 7.41–7.95 (m, 9H, Ar-H), 8.17
(s, 1H, H-4), 9.67 (bs, 1H, NH). Anal. calcd. for C19H11N3O2S
(345.38): C, 66.08; H, 3.21; N, 12.17; S, 9.28. Found: C, 65.85; H, 3.33;
N, 12.12; S, 9.10.
3-Hydroxy-chromeno[2,3-b]pyrazolo[4,3-e]pyridin-5(1H)-one (24)
A mixture of 1 (0.513 g, 3 mmol) and pyrazolidine-3,5-dione (19) (0.759 g,
3 mmol) in absolute ethanol (20 mL) and DBU (0.1 mL) was refluxed for
15 min. The yellow crystals obtained during heating were filtered and
recrystallized from DMF=H2O to give 24, mp > 320ꢀC, yield 48%. IR
(KBr, cmꢁ1): 3350 (OH), 3203 (NH), 3068 (CHarom.), 1657 (C¼Opyrone),
1
1608 (C¼N). H NMR (DMSO, d): 7.52 (t, 1H, H-7), 7.60 (d, 1H, H-9),
7.83 (t, 1H, H-8), 8.16 (d, 1H, H-6), 8.83 (s, 1H, H-4), 9.48 (s, 1H, NH),
13.56 (s, 1H, OH). Anal. calcd. for C13H7N3O3 (253.22): C, 61.66; H, 2.79;
N, 16.59. Found: C, 61.60; H, 2.73; N, 16.42.
2,2-Dimethyl-1,3-dihydro-chromeno[2,3-b]quinoline-4,6(4H,6H)-dione (25)
A mixture of 1 (0.513 g, 3 mmol) and 5,5-dimethyl-cyclohexane-1,3-dione
(20) (0.88 g, 3 mmol) in absolute ethanol (20 mL) and DBU (0.1 mL) was
refluxed for 15 min. The white crystals obtained during heating were fil-
tered and recrystallized from DMF=EtOH to give 25, mp 237ꢀC, yield
57%. IR (KBr, cmꢁ1): 3086 (CHarom.), 2955, 2899 2873 (CH2, CH3),
1684 (C¼O), 1652 (C¼Opyrone), 1595 (C¼N). 1H NMR (DMSO, d):
1.08 (s, 6H, 2 CH3), 2.65 (s, 2H, CH2), 3.10 (s, 2H, CH2), 7.53–8.15
(m, 4H, Ar-H), 8.82 (s, 1H, H-5). M=z (I %): 293 (29), 278 (12), 265
(12), 237 (100), 209 (16), 181 (6), 127 (16), 104 (21), 92 (16), 65 (23). Anal.

3542
M. A. Ibrahim
calcd. for C18H15NO3 (293.33): C, 73.71; H, 5.15; N, 4.78. Found: C,
73.71; H, 5.14; N, 4.74.
2-Oxo(thioxo)-chromeno[30,20:5,6]pyrido[2,3-d]pyrimidine-4,6(1H,3H)-
dione (26a, 26b)
A mixture of 1 (0.513 g, 3 mmol) and barbituric and thiobarbituric acids
(21a and 21b) (3 mmol) in absolute ethanol (20 mL) and DBU (0.1 mL)
was refluxed for 15 min. The solid obtained during heating was filtered
and recrystallized to give 26a and 26b. Compound 26a, recrystallized
from dioxane, mp > 320ꢀC, yield 66%. IR (KBr, cmꢁ1): 3184 (2 NH),
3098 (CHarom), 1707 (2 C¼O), 1650 (C¼Opyrone), 1607 (C¼N). 1H
NMR (DMSO, d): 7.48 (t, 1H, H-8), 7.76 (t, 1H, H-10), 7.93 (t, 1H,
H-9), 8.05 (t, 1H, H-7), 8.85 (s, 1H, H-5), 11.78 (bs, 1H, NH), 11.94
(bs, 1H, NH). M=z (I %): 281 (100), 238 (31), 210 (33), 181 (6), 155 (3),
127 (8), 120 (3), 92 (7), 63 (7). Anal. calcd. for C14H7N3O4 (281.23): C,
59.79; H, 2.51; N, 14.94. Found: C, 59.74; H, 2.48; N, 14.91. Compound
26b, recrystallized from dioxane, mp > 320ꢀC, yield 63%. IR (KBr, cmꢁ1):
1
3250 (2 NH), 3064 (CHarom.), 1664 (2 C¼O), 1606 (C¼N). H NMR
(DMSO, d): 7.53 (t, 1H, H-8), 7.64 (d, 1H, H-10), 7.84 (t, 1H, H-9),
8.09 (d, 1H, H-7), 8.78 (s, 1H, H-5), 11.83 (bs, 2H, 2 NH). Anal. Calcd
for C14H7N3O3S (297.23): C, 56.56; H, 2.37; N, 14.13; S, 10.79. Found
C, 56.42; H, 2.31; N, 14.08; S, 10.78.
N-Acetyl-N-(2,5-dioxo-1,5-dihydro-2H-chromeno[2,3-b]pyridin-3-
yl)benzamide (29)
A mixture of 1 (0.513 g, 3 mmol) and hippuric acid (0.537 g, 3 mmol) in
acetic anhydride (15 mL) was refluxed for 2 h. The reddish crystals
obtained after cooling were filtered, washed several times with water,
and recrystallized from AcOH to give 29, mp 257–258ꢀC, yield 59%.
IR (KBr, cmꢁ1): 3400 (NH), 3058 (CHarom.), 1739 (C¼O), 1703 (C¼O),
1672 (C¼Opyrone), 1640 (C¼Oamide), 1607 (C¼N).1H NMR (DMSO,
d): 2.31 (s, 3H, CH3), 7.35–8.02 (m, 8H, Ar-H), 8.11 (d, 1H, H-6), 8.80
(s, 1H, H-4), 9.83 (s, 1H, NH). Anal. calcd. for C21H14N2O5 (374.36):
C, 67.38; H, 3.77; N, 7.48. Found: C, 67.34; H, 3.68; N, 7.25.
2-Phenyl-5-oxo-5H-[1,3]oxazolo[5,4-b]-chromeno[3,2-e]pyridine (31)
A mixture of 1 (0.513 g, 3 mmol) and hippuric acid (0.537 g, 3 mmol) in
acetic anhydride (15 mL) and freshly fused sodium acetate (0.2 g) was

Novel Chromeno[2,3-b]pyridines
3543
refluxed for 1 h. The yellow crystals obtained after cooling were filtered,
washed several times with water, and recrystallized from AcOH to give
31, mp 273–274ꢀC, yield 68%. IR (KBr, cmꢁ1): 3065 (CHarom.), 1658
(C¼Opyrone), 1633 (C¼N). 1H NMR (DMSO, d): 7.33–8.09 (m, 8H,
Ar-H), 8.25 (d, 1H, H-6), 8.64 (s, 1H, H-4). M=z (I %): 314 (5), 252
(100), 237 (21), 211 (14), 183 (28), 165 (6), 155 (20), 127 (31), 120 (10),
104 (16), 77 (14), 64 (33). Anal. calcd. for C19H10N2O3 (314.36): C,
72.61; H, 3.21; N, 8.91. Found: C, 72.58; H, 3.18; N, 8.90.
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