Solvent-free synthesis of novel 5-oxo-5H-chromeno[4,3-b]pyridine derivatives

Article abstract of DOI:10.1007/s10593-013-1217-1

An efficient and simple method for the synthesis of new 5-oxo-5H-chromeno[4,3-b]pyridine derivatives via Michael addition of 4-aminocoumarin to arylidenemalononitrile for 20 min at 150 C without any solvent is proposed. The advantages of this procedure ar

Full text of DOI:10.1007/s10593-013-1217-1

Chemistry of Heterocyclic Compounds, Vol. 48, No. 12, March, 2013 (Russian Original Vol. 48, No. 12, December, 2012)
SOLVENT-FREE SYNTHESIS OF NOVEL 5-OXO-
5H-CHROMENO[4,3-b]PYRIDINE DERIVATIVES
R. Motamedi1*
An efficient and simple method for the synthesis of new 5-oxo-5H-chromeno[4,3-b]pyridine derivatives
via Michael addition of 4-aminocoumarin to arylidenemalononitrile for 20 min at 150°C without any
solvent is proposed. The advantages of this procedure are mild reaction conditions, high yields of
products, and operational simplicity.
Keywords: 5-oxo-5H-chromeno[4,3-b]pyridine, Michael addition, solvent-free synthesis.
Various coumarin derivatives, particularly those fused with other heterocycles, have attracted much
attention in recent years due to their biological activities [1, 2], and encouraged research to improve the
availability of these compounds with regard to procedures and substrates. Coumarins condensed to pyridine ring
(chromeno[3,4-b]pyridin-5-ones) are also under investigation, as they constitute the backbone of naturally
occurring alkaloids, e.g. santiagonamine [3]. Some of them, both natural and non-natural products, are currently
in clinical trials [4-7].
Previously we reported the synthesis and cytotoxic activity of novel coumarin derivatives,
chromeno[4,3-b]-quinolines, benzopyrano[3,2-c]chromene-6,8-diones and chromeno[3',4']pyrano[2,3-b]quinoline-
6,9-diones [8-10]. In continuation of our studies, and owing to the importance of chromenopyridines, we
decided to investigate the synthesis of new 5-oxo-5H-chromeno[4,3-b]pyridine derivatives by a simple method.
The literature data on existing synthetic routes to 5-oxo-5H-chromeno[4,3-b]pyridines can be classified
based on the functionality of the starting materials. Synthetically significant approaches include multistep ring
formation by reaction of 4-aminocoumarin with alkyl vinyl ketones [11], 4-amino-3-formylcoumarin with C–H
acids [12], 4-chloro-3-formylcoumarin with Wittig phosphoranes [13], or 4-oxo-4H-chromene-3-carbaldehydes
with enamines followed by oxidation [14]. In another procedure, 7-trifluoromethyl group-containing 5-oxo-5H-
chromeno[4,3-b]pyridine derivatives were prepared by reaction of 4-chloro-3-(trifluoroacetyl)-2H-chromen-2-one
and aniline followed by intramolecular cyclization in the presence of concentrated sulfuric acid [15]. However,
these methods have disadvantages such as harsh reaction conditions, sensitivity of starting materials and
reagents to moisture, and use of toxic reagents (POCl3, TMSCl) or oxidants (CrO3, conc. H2SO4).
In the present work, we have developed the synthesis of new 2-amino-4-aryl-5-oxo-5H-chromeno-
[4,3-b]pyridine-3-carbonitriles 3a-n via Michael addition of 4-aminocoumarin (1) to arylidenemalononitrile
2a-n in 60–80% yields in a solvent-free system at 150°C.
[
_______
*To whom correspondence should be addressed, e-mail: r_motamedi@pnu.ac.ir.
1Payame Noor University, PO Box 19395-4697, Lashkarak Road, Tehran, I. R. Iran.
________________________________________________________________________________________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1963-1967, December, 2012.
Original article submitted March 12, 2012.
0009-3122/13/4812-1839©2013 Springer Science+Business Media New York
1839

The starting materials, 4-aminocoumarin (1) and arylidenemalononitriles 2a-n were obtained by known
methods [10, 16-20]. In our condensation protocol, no organic solvents or catalysts were used in the reaction
process. The crude products 3a-n were obtained as solids which were further purified by flash column
chromatography and characterized by 1H NMR, FT-IR, and mass spectra.
CN
CN
NH2
2
CN
3
1 N
NH2
O
10
7
4
9
8
Neat, 150°C
+
R
R
5
6
O
O
O
3a–n
1
2a–n
2, 3 a R = 3-NO2, b R = 4-NO2, c R = 2-Cl, d R = 3-Cl, e R = 4-Cl, f R = 2-Br, g R = 3-Br,
h R = 4-Br, i R = 2-MeO, j R = 3-MeO, k R = 4-MeO, l R = 2-Me, m R = 3-Me, n R = 4-Me
1
The H NMR spectra of compounds 3a-n contain the corresponding signals of coumarin and aryl
protons at 7.00-8.39 ppm, and the broad signal of the NH2 group protons at 8.05-8.35 ppm. Also, the IR spectra
revealed the presence of amino and cyano functions by the respective absorption bands at 3330-3500 and
2211-2228 cm-1.
A putative mechanism for the formation of the products 3 is outlined below.
_
N
N
N
H
CN
+
CN
CN
NH2
O
NH2
NH2
H
H
Ar
Ar
Ar
H
O
O
O
O
O
A
_
N
NH2
NH
H
CN
Ar
CN
H
H
+
N
O
H2N
HN
O
CN
H
–H2
Ar
Ar
O
O
O
O
3
The reaction occurs via the initial formation of the intermediate A as a result of Michael addition of
substituted arylidenemalononitriles 2 and 4-aminocoumarin (1). The Michael adduct A then cyclizes,
isomerizes, and subsequently loses a hydrogen molecule to afford the fully aromatized compounds 3.
In summary, a new Michael addition approach to novel 5-oxo-5H-chromeno[4,3-b]pyridines is reported,
starting from easily accessible arylidenemalononitrile and 4-aminocoumarin. The described method can be
applied to achieve good yields and short reaction times in a solvent-free system to obtain chromenopyridin-
5-one (benzopyranopyridin-5-one) derivatives substituted at position 4 with the aromatic moiety, which are not
easily accessible by other methods.
1840

EXPERIMENTAL
The IR spectra were recorded on a Nicolet Magna 550 FT-IR spectrometer in KBr pellets. 1H and 13C NMR
spectra were recorded using a Bruker 500 spectrometer (500 and 125 MHz, respectively) in DMSO-d6 with
TMS as internal standard. Mass spectra were recorded with a Finnegan MAT TSQ-70 spectrometer (EI, 70 eV).
Melting points were determined on a Kofler hot stage apparatus. Elemental analysis was carried out on a Vario
EL III CHNS-analyzer. The purity of obtained compounds was confirmed by TLC using different mobile
phases. All chemicals and solvents used in this study were purchased from Merck and Sigma-Aldrich.
4-Aminocoumarin (1) was obtained in 90% yield by melting 4-hydroxycoumarin in the presence of
excess NH4OAc for 30 min. 1H NMR and mass spectra of the product were in agreement with those reported in
the literature [10]. The arylidenemalononitriles 2a-n were synthesized by the Knoevenagel condensation of the
corresponding arylaldehydes with malononitrile in aqueous MeOH (H2O–MeOH, 1:1) at room temperature in
90-95% yields. The structures of compounds 2a-n were confirmed by comparison of their spectroscopic data
(IR, 1H NMR, and mass spectra) with those reported in the literature [16-20].
2-Amino-4-aryl-5-oxo-5H-chromeno[4,3-b]pyridine-3-carbonitriles
3
(General Method). The
corresponding arylidenemalononitrile 2a-n (5.4 mmol) and 4-aminocoumarin (1) (870 mg, 5.4 mmol) were
thoroughly mixed in a beaker using spatula. Then the beaker was placed in an autoclave (150°C) for 20 min,
after which the reaction was completed (TLC). The solid crude product was purified by flash column
chromatography, eluting with EtOAc–petroleum ether (20:70) to give pure yellowish crystals of compounds
3a-n.
2-Amino-4-(3-nitrophenyl)-5-oxo-5H-chromeno[4,3-b]pyridine-3-carbonitrile (3a). Yield 1.55 g
(80%). Mp 276-278°C. IR spectrum, , cm-1: 3333, 3452 (NH2), 3223 (C–H), 2228 (CN), 1739 (C=O), 1554,
1348 (NO2). 1H NMR spectrum, δ, ppm (J, Hz): 7.37 (1H, d, J = 8.0, H-7); 7.45 (1H, t, J = 8.0, H-9); 7.69 (1H,
3
4
dt, J = 8.0, J = 1.5, H-8); 7.80 (1H, t, J = 8.0, H-5'); 7.88 (1H, d, J = 8.0, H-6'); 8.32 (2H, br. s, NH2);
8.33-8.35 (2H, m, H-2',4'); 8.39 (1H, d, J = 8.0, H-10). Mass spectrum, m/z (Irel, %): 358 [M]+ (25), 326 (30),
311 (15), 262 (100), 57 (35). Found, %: C 63.63; H 2.79; N 15.63. C19H10N4O4. Calculated, %: C 63.69; H 2.81;
N 15.64.
2-Amino-4-(4-nitrophenyl)-5-oxo-5H-chromeno[4,3-b]pyridine-3-carbonitrile (3b). Yield 1.47 g
(76%). Mp 316-317°C. IR spectrum, , cm-1: 3338, 3431 (NH2), 3234 (C–H), 2222 (CN), 1733 (C=O), 1558,
1350 (NO2). 1H NMR spectrum, δ, ppm (J, Hz): 7.37 (1H, d, J = 8.0, H-7); 7.45 (1H, t, J = 8.0, H-9); 7.69-7.73
(3H, m, H-8,2',6'); 8.10 (2H, br. s, NH2); 8.34 (2H, d, J = 8.4, H-3',5'); 8.38 (1H, d, J = 8.0, H-10). Mass
spectrum, m/z (Irel, %): 358 [M]+ (100), 328 (56), 311 (25), 238 (9). Found, %: C 63.67; H 2.77; N 15.61.
C19H10N4O4. Calculated, %: C 63.69; H 2.81; N 15.64.
2-Amino-4-(2-chlorophenyl)-5-oxo-5H-chromeno[4,3-b]pyridine-3-carbonitrile (3c). Yield 1.63 g
(87%). Mp 258-260°C. IR spectrum, , cm-1: 3483, 3334 (NH2), 3214 (C–H), 2217 (CN), 1732 (C=O). 1H NMR
spectrum, δ, ppm (J, Hz): 7.37 (1H, d, J = 8.0, H-7); 7.39 (1H, d, J = 8.0, H-6'); 7.43-7.51 (3H, m, H-9,4',5');
7.58 (1H, d, J = 8.0, H-3'); 7.70 (1H, t, J = 8.0, H-8); 8.31 (2H, br. s, NH2); 8.38 (1H, d, J = 8.0, H-10). Mass
spectrum, m/z (Irel, %): 349 [M+2]+ (22), 347 [M]+ (72), 330 (2), 312 (10), 201 (30), 104 (100), 77 (30). Found,
%: C 65.58; H 2.88; N 12.05. C19H10ClN3O2. Calculated, %: C 65.62; H 2.90; N 12.08.
2-Amino-4-(3-chlorophenyl)-5-oxo-5H-chromeno[4,3-b]pyridine-3-carbonitrile (3d). Yield 1.69 g
1
(90%). Mp 254-256°C. IR spectrum, , cm-1: 3379 (NH2), 3197 (C–H), 2208 (CN), 1697 (C=O). H NMR
spectrum, δ, ppm (J, Hz): 7.32 (1H, dt, 3J = 7.0, 4J = 2.0, H-6'); 7.36 (1H, d, J = 8.0, H-7); 7.42 (1H, t, J = 8.0,
3
4
H-9); 7.48-7.53 (3H, m, H-2',4',5'); 7.67 (1H, dt, J = 8.0, J = 1.5, H-8); 8.35 (2H, br. s, NH2); 8.37 (1H, dd,
3J = 8.0, 4J = 1.5, H-10). Mass spectrum, m/z (Irel, %): 349 [M+2]+ (22), 347 [M]+ (72), 346 (100), 330 (4.5), 312
(4.5), 228 (4), 201 (5). Found, %: C 65.59; H 2.89; N 12.04. C19H10ClN3O2. Calculated, %: C 65.62; H 2.90;
N 12.08.
2-Amino-4-(4-chlorophenyl)-5-oxo-5H-chromeno[4,3-b]pyridine-3-carbonitrile (3e). Yield 1.26 g
(67%). Mp 305-307°C. IR spectrum, , cm-1: 3396, 3500 (NH2), 3077 (C–H), 2212 (CN), 1725 (C=O). 1H NMR
1841

spectrum, δ, ppm (J, Hz): 7.36 (1H, d, J = 8.0, H-7); 7.39 (2H, d, J = 8.5, H-3',5'); 7.42 (1H, t, J = 8.0, H-9);
7.53 (2H, d, J = 8.5, H-2',6'); 7.68 (1H, dt, 3J = 8.0, 4J = 1.5, H-8); 8.19 (2H, br. s, NH2); 8.38 (1H, dd, 3J = 8.0,
4J = 1.5, H-10). Mass spectrum, m/z (Irel, %): 349 [M+2]+ (22), 347 [M]+ (67), 346 (100), 330 (5), 318 (5), 228
(5), 201 (5). Found, %: C 65.58; H 2.87; N 12.05. C19H10ClN3O2. Calculated, %: C 65.62; H 2.90; N 12.08.
2-Amino-4-(2-bromophenyl)-5-oxo-5H-chromeno[4,3-b]pyridine-3-carbonitrile (3f). Yield 1.80 g
(85%). Mp 242-244°C. IR spectrum, , cm-1: 3323, 3469 (NH2), 3213 (C–H), 2214 (CN), 1727 (C=O). 1H NMR
spectrum, δ, ppm (J, Hz): 7.36-7.39 (2H, m, H-7,4'); 7.42-7.46 (2H, m, H-9,6'); 7.61-7.70 (3H, m, H-8,3',5');
3
4
8.15 (2H, br. s, NH2); 8.38 (1H, dd, J = 8.0, J = 1.5, H-10). Mass spectrum, m/z (Irel, %): 393/391 [M]+ (66),
392 (100), 312 (33), 228 (17), 201 (20), 76 (32), 63 (32). Found, %: C 58.14; H 2.50; N 10.75. C19H10BrN3O2.
Calculated, %: C 58.18; H 2.57; N 10.71.
2-Amino-4-(3-bromophenyl)-5-oxo-5H-chromeno[4,3-b]pyridine-3-carbonitrile (3g). Yield 1.48 g
(70%). Mp 244-246°C. IR spectrum, , cm-1: 3321, 3463 (NH2), 3218 (C–H), 2212 (CN), 1726 (C=O). 1H NMR
spectrum, δ, ppm (J, Hz): 7.37-7.39 (2H, m, H-7,2'); 7.41 (1H, dt, 3J = 8.0, 4J = 1.5, H-6'); 7.45 (1H, t, J = 8.0,
H-9); 7.51 (1H, t, J = 7.5, H-5'); 7.68 (1H, t, J = 8.0, H-8); 7.74 (1H, d, J = 8.0, H-4'); 8.05 (2H, br. s, NH2);
8.38 (1H, dd, 3J = 8.0, 4J = 1.5, H-10). Mass spectrum, m/z (Irel, %): 393/391 [M]+ (64), 312 (100), 284 (5), 125
(5). Found, %: C 58.15; H 2.52; N 10.68. C19H10BrN3O2. Calculated, %: C 58.18; H 2.57; N 10.71.
2-Amino-4-(4-bromophenyl)-5-oxo-5H-chromeno[4,3-b]pyridine-3-carbonitrile (3h). Yield 1.59 g
(75%). Mp 290-292°C. IR spectrum, , cm-1: 3393, 3489 (NH2), 3100 (C–H), 2219 (CN), 1722 (C=O). 1H NMR
spectrum, δ, ppm (J, Hz): 7.33 (2H, d, J = 9.0, H-2',6'); 7.37 (1H, d, J = 8.0, H-7); 7.42 (1H, t, J = 8.5, H-9);
7.66 (1H, t, J = 8.0, H-8); 7.68 (2H, d, J = 9.0, H-3',5'); 8.10 (2H, br. s, NH2); 8.37 (1H, d, J = 8.0, H-10). Mass
spectrum, m/z (Irel, %): 393/391 [M]+ (63), 392 (100), 312 (9), 284 (7), 228 (8), 201 (9). Found, %: C 58.13;
H 2.53; N 10.64. C19H10BrN3O2. Calculated, %: C 58.18; H 2.57; N 10.71.
2-Amino-4-(2-methoxyphenyl)-5-oxo-5H-chromeno[4,3-b]pyridine-3-carbonitrile (3i). Yield 0.65 g
(35%). Mp 209-211°C. IR spectrum, , cm-1: 3349, 3431 (NH2), 3214 (C–H), 2223 (CN), 1722 (C=O). 1H NMR
spectrum, δ, ppm (J, Hz): 4.07 (3H, s, OCH3); 7.12 (1H, d, J = 8.0, H-3'); 7.47-7.53 (2H, m, H-5',6'); 7.68-7.76
(3H, m, H-7,9,4'); 8.03 (1H, t, J = 8.0, H-8); 8.20 (2H, br. s, NH2); 8.32 (1H, d, J = 8.0, H-10). Mass spectrum,
m/z (Irel, %): 343 [M]+ (19), 300 (6), 167 (25), 149 (100), 105 (75), 76 (50), 43 (25). Found, %: C 69.92; H 3.78;
N 12.22. C20H13N3O3. Calculated, %: C 69.96; H 3.82; N 12.24.
2-Amino-4-(3-methoxyphenyl)-5-oxo-5H-chromeno[4,3-b]pyridine-3-carbonitrile (3j). Yield 1.44 g
1
(78%). Mp 260-262°C. IR spectrum, , cm-1: 3374 (NH2), 3181 (C–H), 2192 (CN), 1707 (C=O). H NMR
spectrum, δ, ppm (J, Hz): 4.76 (3H, s, OCH3); 6.88 (1H, d, J = 8.0, H-6'); 6.92 (1H, s, H-2'); 7.01 (1H, dt,
4
3J = 8.0, J = 2.0, H-4'); 7.34 (1H, d, J = 8.0, H-7); 7.38 (1H, t, J = 8.0, H-5'); 7.41 (1H, t, J = 8.0, H-9); 7.66
3
4
3
4
(1H, dt, J = 8.0, J = 1.5, H-8); 8.05 (2H, br. s, NH2); 8.37 (1H, dd, J = 8.0, J = 1.5, H-10). Mass spectrum,
m/z (Irel, %): 343 [M]+ (100), 328 (23), 312 (23), 300 (31), 270 (10), 201 (13), 190 (20), 76 (23), 63 (67). Found,
%: C 69.92; H 3.79; N 12.24. C20H13N3O3. Calculated, %: C 69.96; H 3.82; N 12.24.
2-Amino-4-(4-methoxyphenyl)-5-oxo-5H-chromeno[4,3-b]pyridine-3-carbonitrile (3k). Yield 1.39 g
1
(75%). Mp 259-261°C. IR spectrum, , cm-1: 3349, 3431 (NH2), 3239 (C–H), 2214 (CN), 1734 (C=O). H NMR
spectrum, δ, ppm (J, Hz): 3.83 (3H, s, OCH3); 7.00 (2H, d, J = 8.5, H-2',6'); 7.30 (2H, d, J = 8.5, H-3',5'); 7.33 (1H,
d, J = 8.0, H-7); 7.40 (1H, t, J = 8.0, H-9); 7.65 (1H, t, J = 8.0, H-8); 8.10 (2H, br. s, NH2); 8.37 (1H, d, J = 8.0,
13
H-10). C NMR spectrum, δ, ppm: 55.1; 94.2; 105.2; 113.3 (2C); 115.3; 116.6; 118.3; 124.3; 125.3; 129.0 (2C);
129.2; 133.4; 153.1; 155.1; 157.3; 159.5; 160.0; 160.9. Mass spectrum, m/z (Irel, %): 343 [M]+ (100), 328 (3), 314
(2), 300 (13), 271 (2), 201 (2), 190 (3). Found, %: C 69.85; H 3.89; N 12.20. C20H13N3O3. Calculated, %: C 69.96; H
3.82; N 12.24.
2-Amino-4-(2-methylphenyl)-5-oxo-5H-chromeno[4,3-b]pyridine-3-carbonitrile (3l). Yield 1.15 g
(65%). Mp 270-272°C. IR spectrum, , cm-1: 3331, 3468 (NH2), 3218 (C–H), 2211 (CN), 1730 (C=O). 1H NMR
spectrum, δ, ppm (J, Hz): 2.05 (3H, s, CH3); 7.10 (1H, d, J = 6.5, H-3'); 7.26 (1H, t, J = 6.5, H-4'); 7.31-7.33
(2H, m, H-5',6'); 7.35 (1H, d, J = 8.0, H-7); 7.44 (1H, t, J = 8.0, H-9); 7.67 (1H, t, J = 8.0, H-8); 8.10
1842

(2H, br. s, NH2); 8.39 (1H, d, J = 8.0, H-10). Mass spectrum, m/z (Irel, %): 327 [M]+ (26), 312 (26), 310 (100),
299 (6), 201 (5), 163 (7). Found, %: C 73.34; H 3.97; N 12.82. C20H13N3O2. Calculated, %: C 73.38; H 4.00;
N 12.84.
2-Amino-4-(3-methylphenyl)-5-oxo-5H-chromeno[4,3-b]pyridine-3-carbonitrile (3m). Yield 0.71 g
(40%). Mp 241-243°C. IR spectrum, , cm-1: 3327, 3456 (NH2), 3216 (C–H), 2211 (CN), 1729 (C=O). 1H NMR
spectrum, δ, ppm (J, Hz): 2.35 (3H, s, CH3); 7.11 (1H, d, J = 7.5, H-6'); 7.13 (1H, s, H-2'); 7.26 (1H, d, J = 7.5,
H-4'); 7.35 (1H, d, J = 7.5, H-7); 7.35 (1H, t, J = 7.5, H-5'); 7.41 (1H, t, J = 7.5, H-9); 7.66 (1H, t, J = 7.5, H-8);
8.10 (2H, br. s, NH2); 8.38 (1H, d, J = 7.5, H-10). Mass spectrum, m/z (Irel, %): 327 [M]+ (87), 326 (100), 312
(6), 298 (6), 274 (6), 144 (16), 105 (20). Found, %: C 73.35; H 3.92; N 12.80. C20H13N3O2. Calculated, %:
C 73.38; H 4.00; N 12.84.
2-Amino-4-(4-methylphenyl)-5-oxo-5H-chromeno[4,3-b]pyridine-3-carbonitrile (3n). Yield 0.97 g
(55%). Mp 294-296°C. IR spectrum, , cm-1: 3348, 3468 (NH2), 3213 (C–H), 2212 (CN), 1716 (C=O). 1H NMR
spectrum, δ, ppm (J, Hz): 2.38 (3H, s, CH3); 7.22 (2H, d, J = 8.5, H-3',5'); 7.26 (2H, d, J = 8.5, H-2',6'); 7.33
(1H, d, J = 8.0, H-7); 7.41 (1H, t, J = 8.0, H-9); 7.66 (1H, t, J = 8.0, H-8); 8.10 (2H, br. s, NH2); 8.37 (1H, d,
J = 8.0, H-10). Mass spectrum, m/z (Irel, %): 327 [M]+ (68), 326 (100), 310 (4), 298 (4), 210 (12), 105 (62), 77
(14). Found, %: C 73.33; H 3.95; N 12.82. C20H13N3O2. Calculated, %: C 73.38; H 4.00; N 12.84.
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