Facile eco-friendly synthesis of novel chromeno[4,3-b]pyridine-2,5-diones and evaluation of their antimicrobial and antioxidant properties

Article abstract of DOI:10.1007/s12039-013-0565-9

Rapid and facile access to novel chromeno[4,3-b]pyridine-2,5-dione derivatives was achieved by a mild base catalysed reaction of 4-chloro-3-formylcoumarin and acetoacetamides in PEG-300 as recyclable solvent. The compounds were evaluated for their antimicrobial activities against 3 Gram-positive and 3 Gram-negative bacteria (Staphylococcus epidermis, Vibrio parahaemolyticus, Bacillus subtilis, Escherichia coli, Staphylococcus aureus and Klebsiella pneumonia) with Cefotaxime control. They were further subjected to antioxidant studies using DPPH test with ascorbic acid control. While compounds 5d and 5k showed promising broad spectrum antibacterial properties against all the evaluated bacteria, compound 5g exhibited good antioxidant properties. [Figure not available: see fulltext.]

Full text of DOI:10.1007/s12039-013-0565-9

c
J. Chem. Sci. Vol. 126, No. 1, January 2014, pp. 187–195. ꢀ Indian Academy of Sciences.
Facile eco-friendly synthesis of novel chromeno[4,3-b]pyridine-2,5-diones
and evaluation of their antimicrobial and antioxidant properties
SATYANARAYANA REDDY JAGGAVARAPUa, ANAND SOLOMON KAMALAKARANa,
VENTKATA PRASAD JALLIa, SRAVAN KUMAR GANGISETTYa, MUNUSSWAMY
RAMANUJAM GANESHb and GOPIKRISHNA GADDAMANUGUa,∗
aDepartment of Chemistry, Sankar Foundation Research Institute, Naiduthota, Vishakapatnam 530 047, India
bISISM, SRM university, Kattangulathur, 603 203, India
e-mail: gkrishnagps@gmail.com
MS received 5 June 2013; accepted 13 November 2013
Abstract. Rapid and facileaccess to novel chromeno[4,3-b]pyridine-2,5-dione derivatives was achieved by a
mild base catalysed reaction of 4-chloro-3-formylcoumarin and acetoacetamides in PEG-300 as recyclable sol-
vent. The compounds were evaluated for their antimicrobial activities against 3 Gram-positive and 3 Gram-ne-
gative bacteria (Staphylococcus epidermis, Vibrio parahaemolyticus, Bacillus subtilis, Escherichia coli, Staphy-
lococcus aureus and Klebsiella pneumonia) with Cefotaxime control. They were further subjected to antioxi-
dant studies using DPPH test with ascorbic acid control. While compounds 5d and 5k showed promising broad
spectrum antibacterial properties against all the evaluated bacteria, compound 5g exhibited good antioxidant
properties.
Keywords. Chromeno[4,3-b]pyridine-2,5-diones; acetoacetamide; PEG-300; antimicrobial; antioxidant.
cytotoxic,15 anticancer,16 antimicrobial,17 and antihy-
pertensive properties.18 Aminocoumarins such as novo-
biocin, clorobiocin and coumermycin A1 with nitro-
gen functional group attached to the coumarin ring are
elegant class of antibiotics which inhibit DNA gyrase
enzyme involved in cell division of bacteria.19
1. Introduction
Coumarins and 2-pyridones are classic heterocyclic
scaffolds which constitute vital substructures of seve-
ral natural products and received enormous admi-
ration for their wide range of applications. Secon-
dary metabolites and synthetic intermediates of 2-
pyridone scaffolds demonstrate broad spectrum of syn-
thetic, material and biological applications.1 Ricinine2
with its remarkable CNS stimulant activity was the
first isolated 2-pyridone natural product followed by
the discovery of analogous antibiotic natural products
such as elfamycin,3 ilicolicin4 and efratomycin.5 With
excellent vasodilating properties,6 synthetic 2-pyridone
analogues milrinone and amrinone are extensively
used for the treatment of acute congestive heart fail-
ure. Similarly, L-697,661 was identified as a spe-
cific non-nucleoside reverse transcriptase inhibitor
which demonstrates efficient anti-HIV properties.7 2-
Pyridone is an integral core of several alkaloids8
and is a key structural intermediate in the bacte-
rial metabolism.9 Krawczyk et al. have developed
2-pyridones as novel class of multi-drug resistant
modulators.10 On the other hand, coumarins11 exhibit
excellent antioxidant,12 antibacterial,13 antirhinovirus,14
Fused heterocyclic scaffolds with nitrogen and
oxygen atoms are fundamental to the medicinal che-
mistry for the development of several new drugs. To
date, very few reports are available in the literature
regarding the synthesis of fused chromeno[4,3-
b]pyridine-2,5-dione scaffolds. One of the earliest
documented report by Soliman et al. demonstrates
synthesis of these scaffolds by the reaction of 4-
hydroxycoumarin and aminocrotonitrile.20 In a multi-
step protocol, Heber et al. reported the reaction of
alkylaminocoumarin-3-carbaldehydes with Wittig
ylides to achieve the required targets, albeit in poor
yields.21 Ivanov et al. reported Erlenmeyer–Ploechl
reaction of alkylaminocoumarin-3-carbaldehydes with
N-acetylgylcine derivatives to yield the chromeno[4,3-
b]pyridine-2,5-dione derivatives.22 However, the
method suffers from the limitations of harsh reaction
conditions of refluxing acetic acid and limited to the
synthesis of only N-alkyl derivatives in poor yields.
Similarly, alternative synthesis of these fused systems
reported by Kafka et al. using camphoranils with
∗For correspondence
187

188
Satyanarayana Reddy Jaggavarapu et al.
excess of dimethylmalonate suffer from poor yields.23
Owing to the necessity for an improved methodology
for the synthesis of these fused scaffolds and prevalence
of impressive biological properties of both pyridine-2-
ones and coumarins, we were interested in developing
a mild synthetic protocol for the synthesis of the fused
chromeno[4,3-b]pyridine-2,5-dione scaffolds.
72.50; H 3.95; N, 4.23%]; νmax(KBr) 1719, 1702,
1679, 1618, 1583, 1479, 1418, 1240, 1041 cm−1;
δH (400 MHz CDCl3) 8.73 (1H, s), 7.72 (1H, d, J
6.8 Hz), 7.56–7.50 (4H, m), 7.44–7.43 (2H, m), 7.30
(1H, d, J 6.8 Hz), 7.28–7.25 (1 H, m), 2.71 (3H, s);
δC (100 MHz, CDCl3) δ: 203.42, 159.84, 159.20„
152.57, 145.68, 138.61, 137.14, 133.53, 129.78,
129.64,127.02, 126.07,125.98, 125.13, 118.77, 114.50,
103.35, 31.41, 8.57.; LCMS: MH+, 332.
2. Experimental
The solvents, bases and other general reagents were of
AR grade and purchased from Otto Chemie. H and
2.2b 3-Acetyl-1-(4-fluorophenyl)-1H-chromeno[4,3-b]
pyridine-2,5-dione (5b): White solid, mp 134–135◦C;
[Found: C, 68.70; H, 3.43; N, 4.00. C20H12FNO4
requires C, 68.77; H, 3.46; N, 4.01%]; νmax(KBr) 1721,
1705, 1680, 1621, 1579, 1469, 1421, 1245, 1048 cm−1;
δH (400 MHz CDCl3) 8.69 (1H, s), 7.70 (1H, dd, J
7.6 Hz, J 1.2Hz), 7.58 (1H, td, J 7.6 Hz, J 1.2 Hz),
7.49–7.40 (2H, m), 7.32 (1H, dd, J 6.8 Hz, J 0.8 Hz),
7.30–7.20 (3H, m), 2.70 (3 H, s); δC (100 MHz CDCl3)
203.25, 163.87, 161.87, 159.83, 159.10, 152.54,
145.52, 137.22, 134.49, 133.63, 128.17, 127.01,
125.97, 125.18, 118.80, 116.60, 114.41, 103.51, 31.39;
LCMS: MH+, 350.
1
13C NMR spectra are recorded on 400 MHz Bruker
Biospin FT-NMR spectrometer with CDCl3 as sol-
vent and TMS as internal standard. Melting points
were determined using NETZSCH DSC 200 instru-
ment. IR spectra were recorded over Bruker a alpha-
T spectrophotometer. Mass spectral analysis was car-
ried out using EIMStechniques. Elemental analysis was
performed on Elementar Vario EL III CHNS analyzer.
Analytical thin-layer chromatography (TLC) was per-
formed on 0.2 mm precoated plate Kieselgel 60 F254
(Merck).
2.1 General procedure for synthesis
of acetoacetamides derivatives (3a–p)
2.2c 3-Acetyl-1-(3-fluorophenyl)-1H-chromeno[4,3-b]
pyridine-2,5-dione (5c): White solid, mp 138–139 ◦C;
[Found: C, 68.70; H, 3.43; N, 4.00. C20H12FNO4
requires C, 68.77; H, 3.46; N, 4.01%]; νmax(KBr) 1721,
1705, 1683, 1621, 1587, 1488, 1421, 1243, 1021 cm−1;
δH (400 MHz CDCl3) 8.70 (1H, s), 7.71 (1H, d, J
6.8 Hz), 7.59–7.51 (2H, m), 7.31 (1H, d, J 6.8 Hz),
7.30–7.26 (4H, m), 2.70 (3H, s); δC (100 MHz CDCl3)
203.18,163.59, 161.60, 159.58, 159.03, 152.54, 145.28,
139.66, 139.58, 137.23, 133.69, 131.05, 130.98,
m127.02, 126.07, 125.20, 121.91, 118.80, 117.13,
116.96, 114.35, 114.33, 114.13, 103.65, 31.39; LCMS:
MH+, 350.
To a stirred solution of amine (0.01 mol) in 10 ml of
PEG-300 was added to ethylacetoacatate (0.03 mol) in
100 ml round bottom flask and refluxed at 120 C for
1.5–2 h. After completion of the reaction (monitored
by TLC) the reaction mixture was cooled and extracted
with cold diethyl ether (3 × 10 mL) and purified by col-
umn chromatography (10–25% EtOAc in Hexane) gave
the pure product 3a–p. Final products were confirmed
with the reported literature.24
◦
2.2 General method for the synthesis of 3-acetyl-1-
phenyl-1H-chromeno[4,3-b]pyridine-2,5-dione 5a–p
2.2d 3-Acetyl-1-(4-bromophenyl)-1H-chromeno[4,3-b]
pyridine-2,5-dione (5d): White solid, mp 138–139◦C;
[Found: C, 55.80; H, 2.88. C18H11BrO5 requires C,
55.84; H, 2.86%]; νmax(KBr) 1721, 1705, 1682, 1621,
1577, 1472, 1410, 1233, 1033 cm−1; δH (400 MHz
CDCl3) 7.83–7.77 (2H, m), 7.59–7.51(2H, m), 7.45
(1H, d, J 8.8 Hz), 7.32 (1H, t, J 7.6 Hz), 7.21 (1H,
d, J 8.4 Hz), 6.80 (1H, d, J 8.8 Hz), 2.10 (3H, s); δC
(100 MHz CDCl3)203.14, 159.54, 158.96, 145.18,
To a solution of 4-chloro-3-formylcoumarin 1a
(0.5 mmol) in PEG-300 (2 mL) was added acetoac-
etamides 3a (0.5 mmol) and triethylamine (0.5 mmol)
then stirred at 25◦C for 15 min. The precipitate obtained
was filtered by Whatman filter paper, washed with water
and dried. Similar procedure was employed in case of
substrates 5b–p.
2.2a 3-Acetyl-1-phenyl-1H-chromeno[4,3-b]pyridine- 137.42, 137.11, 133.60, 132.74, 127.71, 126.91,
2, 5-dione (5a): Whitesolid, mp 153–154◦C; [Found: 125.88, 125.13, 123.83, 118.71, 114.29, 103.55, 45.79,
C, 72.42; H, 3.92; N, 4.22. C20H13NO4 requires C, 31.33, 8.56; LCMS: MH+, 411.

Facile eco-friendly synthesis of novel chromeno[4,3-b]pyridine-2,5-diones
189
2.2e 3-Acetyl-1-(3-bromophenyl)-1H-chromeno[4,3-b] 2.2i 3-Acetyl-1-(4-methoxyphenyl)-1H-chromeno[4,
pyridine-2,5-dione (5e): White solid, mp 132–133◦C; 3-b]pyridine-2,5-dione (5i): White solid, mp 230–
[Found: C, 58.56; H, 2.95, N, 3.41. C20H12BrNO4 232◦C; [Found: C, 58.22; H, 2.69; N, 3.75. C21H15NO5
requires C, 58.50; H, 2.92, N, 3.41%]; νmax(KBr) 1723, requires C, 58.23; H, 2.71, N, 3.77%]; νmax(KBr) 1722,
1705, 1683, 1620, 1533, 1480, 1420, 1245, 1033 cm−1; 1708, 1683, 1620, 1579, 1480, 1420, 1239, 1039 cm−1;
δH (400 MHz CDCl3) 8.68 (1H, s), 7.76–7.70 (3H, m), δH (400 MHz CDCl3) 8.70 (1H, s), 7.70 (1H, d, J
7.57 (1H, td, J 6.8 Hz, 0.8 Hz), 7.49–7.38 (3H, m), 6.8 Hz), 7.55 (1H, t, J 6.8 Hz), 7.35–7.22 (4H, m),
7.33 (1H, d, J 6.8 Hz), 7.28 (1H, dd, J 6.8 Hz, 0.8 Hz), 7.02 (1H, d, J 7.2 Hz), 3.86 (3H, s), 2.70 (3H, s); δC
2.70 (3H, s); δC (100 MHz CDCl3) 203.09, 159.55, (100 MHz CDCl3)) 203.50, 160.30, 160.02, 159.22,
158.58, 152.51, 145.20, 139.48, 137.22, 133.67, 152.51, 145.87, 136.97, 133.42, 131.29, 127.20,
132.95, 130.82, 129.37, 127.00, 126.01, 125.18, 125.06, 118.70, 114.70, 103.13, 55,59, 31.38; LCMS:
124.90, 122.90, 118.77, 114.32, 103.64, 58.30, 31.37, MH+, 362.
18.33; LCMS: MH+, 411.
2.2j 3-Acetyl-1-(3-methoxyphenyl)-1H-chromeno
2.2f 3-Acetyl-1-(4-chlorophenyl)-1H-chromeno[4,3-b] [4,3-b]pyridine-2,5-dione (5j): White solid, mp 133–
pyridine-2,5-dione (5f): White solid, mp 130–131◦C; 135◦C; [Found: C, 69.73; H, 4.15; N, 3.87. C21H15NO5
[Found: C, 65.61; H, 3.28, N, 3.82. C19H14O5 requires requires C, 69.80; H, 4.18, N, 3.88%]; νmax(KBr) 1723,
C, 65.67; H, 3.31, N, 3.83%]; νmax(KBr) 1723, 1706, 1707, 1688, 1620, 1579, 1481, 1420, 1240, 1041 cm−1;
1683, 1630, 1579, 1481, 1420, 1238, 1033 cm−1; δH δH (400 MHz CDCl3) 8.71 (1H, s), 7.70 (1H, d, J
(400 MHz CDCl3) 8.67 (1H, s), 7.68 (1H, d, J 6.8 Hz), 6.4 Hz), 7.56 (1H, t, J 6.4 Hz), 7.44 (1H, t, J 6.4 Hz),
7.61–7.46 (3H, m), 7.40 (1H, d, J 7.2 Hz), 7.30 (1H, d, 7.31 (1H, d, J 6.4 Hz), 7.39–7.21 (2H, m), 7.04 (1H,
J 6.4 Hz), 7.25 (1H, t, J 6.0 Hz), 2.68 (3H, s); δC (100 d, J 6.8 Hz), 7.00–6.96 (2H, m), 3.85 (3H, s), 2.71
MHz CDCl3) 203.18, 159.65, 159.02, 152.52, 145.28, (3H, s); δC (100 MHz CDCl3) 203.44, 160.33, 159.15,
137.17, 136.95, 135.85, 133.65, 129.81, 127.48, 152.53, 145.70, 139.57, 137.05, 133.50, 130.40,
126.98, 125.96, 125.18, 118.77, 114.36, 103.59, 60.32, 126.98, 125.93, 125.10, 118.09, 115.76, 114.47,
31.38, 14.13; LCMS: MH+, 366.
111.87, 103.22, 55.58, 31.40; LCMS: MH+, 362.
2.2g 3-Acetyl-1-p-tolyl-1H-chromeno[4,3-b]pyridine- 2.2k 3-Acetyl-1-(3-nitrophenyl)-1H-chromeno[4,3-b]
2,5-dione (5g): White solid, mp 132–133◦C; [Found: pyridine-2,5-dione (5k): White solid, mp 134–136◦C;
C, 73.03; H, 4.38, N, 4.06 C20H16O6requires C, 72.96; [Found: C, 63.77; H, 3.28; N, 7.44. C20H12N2O6
H, 4.38, N, 4.05%]; νmax(KBr) 1722, 1705, 1683, 1621, requires C, 63.83; H, 3.21, N, 7.44%]; νmax(KBr) 1725,
1579, 1480, 1420, 1230, 1039 cm−1; δH (400 MHz 1706, 1681, 1620, 1579, 1477, 1420, 1238, 1038 cm−1;
CDCl3) 8.70 (1H, s), 7.70 (1H, d, J 6.4 Hz), 7.55 (1H, t, δH (400 MHz CDCl3) 8.71 (1H, s), 8.42–8.31 (2H, m),
J 5.6 Hz), 7.33–7.23 (6H, m), 2.69 (3H, s), 2.42 (3H, s); 7.83 (1H, d, J 6.4 Hz), 7.77 (1H, t, J 6.4 Hz), 7.70
δC (100 MHz CDCl3) 203.45, 159.86, 159.15, 152.44, (1H, d, J 6.4 Hz, ), 7.59 (1H, t, J 6.0 Hz), 7.33 (1H,
145.75, 139.91, 136.92, 136.02, 133.37, 130.07, d, J 6.8 Hz), 7.28 (1H, t, J 6.0 Hz), 2.71 (3H, s); δC
126.90, 125.69, 125.00, 118.64, 114.44, 103.10, 31.33, (100 MHz CDCl3) 202.81, 159.50, 158.86, 152.64,
21.08, 18.26; LCMS: MH+, 346.
148.75, 144.65, 139.29, 137.65, 134.02, 132.32,
130.69, 127.16, 126.30, 125.39, 124.65, 121.87,
118.96, 114.27, 104.34, 31.44; LCMS: MH+, 377.
2.2h 3-Acetyl-1-m-tolyl-1H-chromeno[4,3-b]pyridine-
2,5-dione (5h): White solid, mp 138–139◦C; [Found:
C, 73.03; H, 4.38, N, 4.06 C20H16O6requires C, 72.96; 2.2l 3-Acetyl-1-(2-nitrophenyl)-1H-chromeno[4,3-b]
H, 4.38, N, 4.05%]; νmax(KBr) 1721, 1705, 1682, 1623, pyridine-2,5-dione (5l): White solid, mp 138–140◦C;
1579, 1482, 1420, 1241, 1039 cm−1; δH (400 MHz [Found: C, 62.12; H, 3.54; N, 3.81. C19H13NO7 requires
CDCl3) 8.70 (1H, s)), 7.70 (1H, s, J 6.4 Hz), 7.55 (1H, C, 62.13; H, 3.57, N, 3.81%]; νmax(KBr) 1723, 1704,
t, J 5.6 Hz), 7.33–7.23 (6H, m), 2.69 (3H, s), 2.42 1682, 1620, 1579, 1482, 1420, 1218, 1045 cm−1;
(3H, s); δC (100 MHz CDCl3) 203.51, 159.95, 159.30, δH (400 MHz CDCl3) 8.69 (1H, s), 8.23 (1H, d, J
152.63, 145.79, 139.99, 138.58, 137.15, 133.53, 6.4 Hz), 8.12 (1H, d, J 6.8 Hz), 7.82–7.71 (2H, m),
130.59, 129.48, 127.07, 126.62, 125.99, 125.16, 7.77 (1H, t, J 6.4 Hz), 7.70 (1H, t, J 6.4 Hz, ), 7.59
123.07, 118.82, 114.58, 103.27, 31.46, 21.30; LCMS: (1H, t, J 6.0 Hz), 7.33–722 (2H, m), 2.69 (3H, s); δC
MH+, 346.
(100 MHz CDCl3) 160.12, 158.50, 152.57, 151.22,

190
Satyanarayana Reddy Jaggavarapu et al.
144.21, 137.57, 132.38, 125.30, 125.01, 124.01, (2H, m), 5.24 (2H, s), 2.68 (3H, s); δC (100 MHz
120.32, 119.18, 118.12, 117.57, 103.77, 98.56, 91.40, CDCl3) 203.62, 160.09, 159.15, 152.46, 145.08,
23.56, 21.07; LCMS: MH+, 377.
136.77, 134.13, 133.34, 129.27, 128.96, 128.73,
126.88, 125.33, 125.04, 118.67, 114.54, 103.13, 53.22,
31.47; LCMS: MH+, 346.
2.2m 3-Acetyl-1-(pyridin-2-yl)-1H-chromeno[4,3-b]
pyridine-2,5-dione (5m): white solid, mp 132–135◦C;
[Found: C, 68.61; H, 3.61 N, 8.42. C19H12N2O4
requires 68.67; H, 3.64 N, 8.43%]; νmax(KBr) 1724,
1707, 1682, 1621, 1581, 1481, 1421, 1239, 1040 cm−1;
δH (400 MHz CDCl3) δ 9.04 (1H, s), 8.69 (1H, s),
8.08 (1H, t, J 6.0 Hz), 7.93 (1H, d, J 5.4 Hz), 7.69–
7.59 (3H, m), 7.41–7.36 (2H, m), 2.64 (3H, s); δC
(100 MHz CDCl3) 188.30, 186.10, 165.55, 161.27,
159.09, 154.79, 135.93, 135.47, 129.64, 125.86,
125.72, 125.45, 124.67, 117.46, 116.49, 114.45,
110.17; LCMS: MH+, 333.
3. Results and discussions
Application of green and sustainable chemistry pro-
tocols has seen enormous surge in recent times for
the development of novel and eco-friendly methodo-
logies towards the synthesis of valuable synthetic
scaffolds and drug intermediates. Polyethylene gly-
col (PEG) has gained wide popularity as alternative
solvent in contributing to such green methodologies
by successfully plummeting the generation of indus-
trial waste.25
We have earlier demonstrated the utility of 4-chloro-
3-formylcoumarin as a versatile starting material for
the syntheses of various privileged heterocycles such
as chromeno-quinolines,26a chromeno-benzazepines,26b
chromeno-pyrimidine-N-oxides26c and chromeno-
trioxabicylco[3,3,1]nonadienes.26d In continuation of
our efforts to synthesize novel heterocyclic molecules
of biological importance, we envisaged a mild base
mediated synthesis of the target molecules from 4-
chloro-3-formylcoumarin and acetoacetamides via si-
multaneous nucleophilic N-alkylation and Knoevenagel
reactions using PEG-300 as a recyclable eco-friendly
solvent.
2.2n 3-Acetyl-1-butyl-1H-chromeno[4,3-b]pyridine-
2,5-dione (5n): White solid, mp 138–141◦C; [Found:
C, 69.37; H, 5.46, N, 4.49. C24H16O5 requires C, 69.44;
H, 5.50, N, 4.50%]; νmax(KBr) 1721, 1707, 1681, 1620,
1579, 1460, 1421, 1219, 1039 cm−1; δH (400 MHz
CDCl3) 8.62 (1H, s), 7.66 (1H, d, J 6.0 Hz), 7.52 (1H,
t, J 6.8 Hz), 7.29 (1H, d, J 6.4 Hz), 7.26–7.21 (1H, m),
4.08 (1H, t, J 6.0 Hz), 2.67 (3H, s), 1.82 (2H, q,), 1.42
(m, 2H), 0.98 (3H, t); δC (100 MHz CDCl3) 203.75,
159.98, 159.31, 152.43, 145.34, 136.63, 133.20,
126.81, 125.13, 124.97, 118.64, 114.58, 102.67, 50.73,
31.42, 31.03, 19.76, 13.48; LCMS: MH+, 312.
2.2o 3-Acetyl-1-ethyl-1H-chromeno[4,3-b]pyridine-
2,5-dione (5o): White solid, mp 132–134◦C; [Found:
C, 67.77; H, 4.58, N, 4.94, C16H13NO4 requires
C, 67.84; H, 4.63, 4.94%]; νmax(KBr) 1725, 1708,
1679, 1621, 1592, 1479, 1456, 1246, 1050 cm−1; δH
(400 MHz CDCl3) 8.67 (1H, s), 7.67 (1H, dd, J 6.4 Hz,
0.8 Hz), 7.54 (1H, td, J 6.8, J 1.2 Hz), 7.31 (1H, dd, J
6.8 Hz, J 0.8 Hz), 7.24 (1H, td, J 6.8, J 0.8 Hz), 4.16
(2H, q, J 5.6 Hz), 2.68 (3H, s), 1.47 (3H, t, J 5.6 Hz);
δC (100 MHz CDCl3) 203.77, 159.86, 159.29, 152.42,
144.97, 136.66, 133.21, 126.80, 125.13, 124.98,
118.64, 114.57, 102.85, 46.05, 31.45, 14.39, 8.54;
LCMS: MH+, 284.
The popular methodologies for the synthesis of ace-
toacetamides in general employ reaction of amines
with excess of ethyl acetoacetate in solvents such as
benzene, toluene or xylenes at reaction temperatures
up to 140◦C.24 As an alternative eco-friendly proce-
dure for the synthesis of starting materials 3a–p, we
explored the possibility of PEG-300 as a benign sol-
vent for their reaction. We found that there are no
reports utilizing PEG-300 as a solvent for the syn-
thesis of the acetoacetamides to date. When the reac-
tion of aniline 1a was conducted in PEG-300 with 1
equivalent of ethyl acetoacetate, the product 3a was
isolated in moderate yields (60%) after 2 h of reac-
tion at 120◦C (table 1, entry 1). Increasing the quan-
tity of ethyl acetoacetate to 2 equivalents resulted
2.2p 3-Acetyl-1-benzyl-1H-chromeno[4,3-b]pyridine-
2,5-dione (5p): White solid, mp 135–137◦C; [Found: in good yields (81%) of the required acetoacetamide
C, 72.97; H, 4.34; N, 4.05 C21H15NO4 requires C, 3a (table 1, entry 2). The present optimized reac-
73.03; H, 4.38, N, 4.06%]; νmax(KBr) 1723, 1705, tion conditions successfully circumvented the utiliza-
1681, 1621, 1592, 1489, 1458, 1247, 1053 cm−1; δH tion of large excess of ethyl acetoacetate unlike the
(400 MHz CDCl3) 8.63 (1H, s), 7.66 (1H, d, J 6.0 Hz), earlier reported methodologies. As shown in table
7.52 (1H, t, J 6.0 Hz), 7.44–7.31 (5H, m), 7.30–7.19 1, the reaction conditions were further exploited for

Facile eco-friendly synthesis of novel chromeno[4,3-b]pyridine-2,5-diones
191
Table 1. Synthesis of acetoacetamides with diverse
Table 2. Screening studies of reaction of acetoacetamide
(3a) and 4-chloro-3-formylcoumarin (4) with various bases
in PEG-300a.
amines and ethyl acetoacetatea.
O
O
O
O
PEG 300
120oC
O
O
R
O
O
R-NH2
N
+
O
H
HN
O
O
1a−p
3a−p
2
N
PEG 300
Base
+
O
Entry
R
Time (h)
Yieldb (%)
O
O
Cl
4
R
3a
3a
3b
3c
3d
3e
3f
3g
3h
3i
Ph
Ph
p-F-Ph
m-F-Ph
p-Br-Ph
m-Br-Ph
p-Cl-Ph
2.0
2.0
2.5
3.0
2.5
3.0
2.5
2.0
2.0
2.0
2.0
3.0
3.0
60c
81
63
60
66
64
68
69
70
73
58
56
66
66
76
74
75
5a
3a
Entry
Base
Et3N
Time
Yieldc (%)
1
2
3
4
5
6
7
15 min
6 h
83b
50
K2CO3
NaHCO3
NaOAc
DMAP
DIEA
6 h
10 h
10 h
60
NRd
NR
78
p-CH3-Ph
m-CH3-Ph
p-OCH3-Ph
m-OCH3-Ph
m-NO2-Ph
o-NO2-Ph
15 min
15 min
DBU
70
3j
3k
3l
aAll the reactions were performed on 0.5 mmol scale with 1
equiv of base in 2 ml solvent at room temperature
3m 2-Aminopyridine 2.0
bPure precipitated yield
cIsolated yields
3n
3o
3p
n-butyl
n-ethyl
n-benzyl
1.5
1.5
1.5
dNo reaction.
aAll the reactions were performed on 0.01 mol scale in 10 ml
solvent at 120◦C
best base from the standardization of reaction condi-
tions. PEG solvent could easily be recycled by wash-
ing with small quantities (5 ml) of diethyl ether.
Our attempts to synthesize the target chromeno[4,3-
bIsolated yields
cOne equivalent of ethyl acetoacetate
the synthesis of acetoacetamides 3b–p (entries 2– b]pyridine-2,5-dione 3a in one-pot procedure starting
16) successfully with a variety of functional groups from aniline 1a unfortunately did not yield satisfactory
in good yields (56–81%). The methodology worked results.
satisfactorily for aryl, heteroaryl and aliphatic sub-
strates.
To validate general feasibility of the methodo-
logy, variety of aromatic and aliphatic acetoacetamides
To further optimize the reaction conditions for the 3b–p were utilized in the reaction with 4-chloro-3-
synthesis of chromeno[4,3-b]pyridine-2,5-diones 5a– formylcoumarin under the optimized reaction condi-
p, 4-choloro-3-formylcoumarin 4 and acetoacetanilide tions. As demonstrated in table 3, halogen substituted
3a were chosen as model substrates. An initial reac- acetoacetamides 3b–f possessing p-fluoro, m-flouro,
tion was attempted where 4 was reacted with ace- p-bromo, m-bromo and p-chloro substituents reacted
toacetamide 3a in PEG-300 employing triethylamine smoothly to afford the corresponding benzopyrano-2-
base. Completion of the reaction was indicated by pyridoneproducts 5b–f in 78–82% yields. While elec-
the formation of a precipitate which could be easi- tron donating substrates 3g–j possessing methyl and
ly filtered from the reaction mixture. To our satisfac- methoxy substituents afforded slightly higher yields
tion, we found that the product obtained was in good (84–90%) of the corresponding products 5g–j, the
yield (83%) and of high purity (table 2, entry 1). To electron withdrawing substrates p-NO2 and m-NO2
ascertain the efficiency of triethylamine, various bases groups afforded 72 and 75% yields of products 5k
as shown in table 2 were screened for the reaction. and 5l, respectively. Heteroaromatic and aliphatic sub-
While bases such as K2CO3 and NaHCO3 gave mod- strates 3m–p also furnished good yields (72–84%)
erate yields (50–60%) of product 5a after 6 h of reac- of coumarino[4,3-b]pyrid-2-one products 5m–p under
tion, surprisingly, sodium acetate and DMAP did not the optimized reaction conditions. The present recy-
catalyse the reaction (table 2, entries 2–5). Competi- clable eco-friendly methodology offers advantages of
tive yields of 5a were observed when DMAP (78%) the obtaining pure precipitates of 5a–p in good to excel-
and DBU (70%) were employed as bases (table 2, lent yields without requirement of tedious purification
entries 6 and 7). Triethylamine was considered as the protocols.

192
Satyanarayana Reddy Jaggavarapu et al.
Table 3. Synthesis of chromeno [4, 3-b] pyridine-2, 5-diones.
O
N
O
O
O
PEG 300,
Et3N (1 eqvi.),
rt, 15 min
HN
O
O
O
+
O
O
Cl
4
5a−p
R
R
3a−p
Entry
1
Acetoacetamide
Chromeno[4,3-b]pyridine-2,5-dione (5a–n)
Yield(%)a
O
O
H
N
N
83
O
O
O
O
3a
5a
O
O
H
N
N
2
3
79
80
O
O
3b
O
F
O
F
5b
O
O
H
N
N
O
O
O
O
3c
Cl
Br
Cl
Br
5c
O
O
H
N
N
4
5
82
78
O
O
O
O
5d
3d
H
N
N
O
O
O
O
O
3e
5e
O
H
N
N
6
7
80
82
O
O
O
O
O
3f
5f
O
O
H
N
N
O
O
O
3g
5g
F
F
O
O
H
N
N
8
87
O
O
O
O
3h
5h
Br
Br

Facile eco-friendly synthesis of novel chromeno[4,3-b]pyridine-2,5-diones
193
Table 3.
(continued)
O
N
O
O
O
PEG 300,
Et3N (1 eqvi.),
rt, 15 min
HN
O
O
O
+
O
O
Cl
4
5a−p
R
R
3a−p
Entry
Acetoacetamide
Chromeno[4,3-b]pyridine-2,5-dione (5a–n)
Yield(%)a
O
O
H
N
N
9
83
O
O
O
O
O
O
5i
3i
O
N
O
H
N
10
85
O
3j
O
O
O
5j
O
O
O
N
O
H
N
O
11
12
75
71
O
O
O
3k
5k
O
NO2
NO2
NO2
O
H
N
N
O
O
NO2
O
O
3l
5l
O
O
H
N
N
N
O
13
72
O
O
O
N
3m
5m
O
O
N
H
N
14
15
16
84
83
80
O
O
3n
O
O
5n
5o
O
N
O
H
N
O
O
O
O
3o
O
O
N
H
N
O
O
O
O
5p
3p
aYields refer to the precipitated products

194
Satyanarayana Reddy Jaggavarapu et al.
Table 4. Evaluation of antibacterial and antioxidant properties for 5a–p.
Entry E. coli (-ve) V. parahaemolyticus K. pneumoniae S. epidermidis B. subtilis S. aureus DPPH inhibition
(-ve)
(-ve)
(+ve)
(+ve)
(+ve)
(%)
5a
5b
5c
5d
5e
5f
5g
5h
5i
>200
>200
>200
6.25
>200
>200
>200
>200
>200
12.5
>200
>200
>200
12.5
>200
>200
>200
>200
>200
50
>200
>200
>200
12.5
>200
>200
>200
>200
>200
50
>200
>200
>200
25
>200
>200
>200
>200
>200
50
>200
>200
>200
12.5
>200
>200
>200
>200
>200
25
>200
>200
>200
3.13
>200
>200
>200
>200
>200
50
80.21
26.23
42.41
39.50
55.48
NA
62.13
NA
36.27
16.39
49.34
NA
5j
5k
5l
12.5
>200
>200
6.25
>200
>200
12.5
>200
>200
3.13
>200
>200
6.25
>200
>200
3.13
>200
>200
5m
29.44
For evaluation of antibacterial properties of the syn- was incubated at 30◦C for 1 h, and the absorbance at
thesized compounds 5a–p (table 4), clinically active 515 nm was measured with a microplate reader. From
Gram-negative Escherichia coli, Vibrio parahaemolyti- the results of the screening studies displayed in table 4,
cus, Klebsiella pneumonia and Gram-positive Staphy- it can be suggested that all the compounds except 5f, 5h,
lococcus epidermidis, Bacillus subtilis, and Staphylo- 5l and 5p exhibit moderate to good antioxidant proper-
coccus aureus bacteria were selected. Dimethyl sulfox- ties. Among the analogs, compound 5g displayed best
ide was chosen as negative control while Cefotoxime antioxidant property with 62.13% inhibition followed
was chosen as positive control due to its broad spectrum by 5e, 5k and 5c with 55.48%, 49.34% and 42.41%
antibacterial activity against both Gram-positive and activities, respectively.
Gram-negative bacteria. The concentration at which the
In summary, a series of novel chromeno[4,3]
compounds inhibited the visible growth of the micro- pyridine-2,5-diones 5a–p were synthesized by a mild
bial cultures was taken as MIC for that compound by eco-friendly high yielding methodology using PEG
using the standard protocol of NCCLS Broth Microdi- as a recyclable solvent. The compounds were further
lution MIC method.27 The MIC values listed in table 4 subjected to antimicrobial and antioxidant screening
suggest that compounds 5d, 5j, 5k, 5n and 5o showed where 5d and 5k displayed potent antimicrobial activi-
promising broad spectrum antibacterial activities. More ties and compound 5g displayed promising antioxidant
specifically, compounds 5d and 5k demonstrated maxi- properties (table 4).
mum activity, where 5d was more selective in inhibiting
Staphylococcus aureus (3.13 μg/mL) and 5k exhibits
maximum activity against both Staphylococcus aureus
Acknowledgements
and Staphylococcus epidermidis (3.13 μg/mL).
We thank the Management of Sankar Foundation for
The evaluation of total antioxidant activities of the
financial support and encouragement. The authors also
compounds 5a–p were evaluated using free radical
thank SAIF, Cochin University of Science and Technol-
scavenging activity determined by 1,1-diphenyl picryl
ogy for elemental analysis.
hydrzyl (DPPH) procedure.28 The inhibition percentage
equation of the radical scavenging the radical scaveng-
ing activity was calculated by using the equation
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