10-(4-Hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-3-methyl-1H,10H-pyrano[4,3-b] chromen-1-ones from a pseudo-multicomponent reaction and evaluation of their antioxidant activity

Article abstract of DOI:10.1016/j.tet.2018.01.009

A series of novel 10-(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-3-methyl-1H,10H-pyrano[4,3-b]chromen-1-ones were synthesized by a pseudo-three-component reaction of 4-hydroxy-6-methyl-2-oxo-2H-pyran-2-one (TAL) with 2-hydroxyarylaldehydes using different acids as catalysts and solvents. The approach relies on a regioselective cascade reaction involving two molar equiv of the TAL iteratively acting as active methylene in a Knoevenagel condensation and in a Michael addition. The antioxidant activity of the synthesized compounds were determined using the DPPH scavenging assay, being the results dependent on the nature and number of chromone substituents. The compound bearing an ortho-dihydroxy (catechol) moiety showed excellent activity at lower concentrations, while derivatives bearing alkoxy groups as substituents present pro-oxidant activity.

Full text of DOI:10.1016/j.tet.2018.01.009

Accepted Manuscript
10-(4-Hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-3-methyl-1H,10H-pyrano[4,3-b]
chromen-1-ones from a pseudo-multicomponent reaction and evaluation of their
antioxidant activity
Liza Saher, Malika Makhloufi-Chebli, Leila Dermeche, Samia Dermeche, Baya
Boutemeur-Khedis, Cherifa Rabia, Maamar Hamdi, Artur M.S. Silva
PII:
S0040-4020(18)30021-8
10.1016/j.tet.2018.01.009
TET 29224
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 12 November 2017
Revised Date: 30 December 2017
Accepted Date: 5 January 2018
Please cite this article as: Saher L, Makhloufi-Chebli M, Dermeche L, Dermeche S, Boutemeur-Khedis
B, Rabia C, Hamdi M, Silva AMS, 10-(4-Hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-3-methyl-1H,10H-
pyrano[4,3-b] chromen-1-ones from a pseudo-multicomponent reaction and evaluation of their
antioxidant activity, Tetrahedron (2018), doi: 10.1016/j.tet.2018.01.009.
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10-(4-Hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-3-methyl-1H,10H-
pyrano[4,3-b]chromen-1-ones from a pseudo-multicomponent
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reaction and evaluation of their antioxidant activity
Liza Sahera,b, Malika Makhloufi-Cheblia,b,*, Leila Dermechea,c, Samia Dermeched, Baya Boutemeur-Khedisb, Cherifa Rabiac, Maamar Hamdib,*, Artur M.
S. Silvae,*
aLab. de Physique Chimie des Materiaux (LPCM), Département de Chimie, Faculté des Sciences, Université Mouloud Mammeri, 15000, Tizi Ouzou,
Algeria. bLab. de Chimie Organique Appliquée (Groupe Hétérocycles), cLab. de Chimie du Gaz Naturel, Faculté de Chimie, Université des Sciences et de
la Technologie Houari Boumediène, BP 32, El-Alia, 16111 Bab-Ezzouar, Alger, Algeria. dLab. de Microbiologie, Département de Biologie, Faculté des
e
Sciences, Université Mouloud Mammeri, 15000, Tizi Ouzou, Algeria. Department of Chemistry & QOPNA, University of Aveiro, 3810-193 Aveiro,
Portugal.

1
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Tetrahedron
journal homepage: www.elsevier.com
10-(4-Hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-3-methyl-1H,10H-pyrano[4,3-b]
chromen-1-ones from a pseudo-multicomponent reaction and evaluation of their
antioxidant activity
Liza Sahera,b, Malika Makhloufi-Cheblia,b,*, Leila Dermechea,c, Samia Dermeched, Baya Boutemeur-
Khedisb, Cherifa Rabiac, Maamar Hamdib,*, Artur M. S. Silvae,*
aLab. de Physique Chimie des Materiaux (LPCM), Département de Chimie, Faculté des Sciences, Université Mouloud Mammeri, 15000 Tizi Ouzou, Algeria.
bLab. de Chimie Organique Appliquée (Groupe Hétérocycles), cLab. de Chimie du Gaz Naturel, Faculté de Chimie, Université des Sciences et de la Technologie
Houari Boumediène, BP 32, El-Alia, 16111 Bab-Ezzouar, Alger, Algeria.
dLab. de Microbiologie, Département de Biologie, Faculté des Sciences, Université Mouloud Mammeri, 15000 Tizi Ouzou, Algeria.
eDepartment of Chemistry & QOPNA, University of Aveiro, 3810-193 Aveiro, Portugal. https://sites.google.com/site/artursilvaua/silva-ams
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
A series of novel 10-(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-3-methyl-1H,10H-pyrano[4,3-
b]chromen-1-ones were synthesized by a pseudo-three-component reaction of 4-hydroxy-6-
methyl-2-oxo-2H-pyran-2-one (TAL) with 2-hydroxyarylaldehydes using different acids as
catalysts and solvents. The approach relies on a regioselective cascade reaction involving two
molar equiv of the TAL iteratively acting as active methylene in a Knoevenagel condensation
and in a Michael addition. The antioxidant activity of the synthesized compounds were
determined using the DPPH scavenging assay, being the results dependent on the nature and
number of chromone substituents. The compound bearing an ortho-dihydroxy (catechol) moiety
showed excellent activity at lower concentrations, while derivatives bearing alkoxy groups as
substituents present pro-oxidant activity.
Available online
Keywords:
Pyranyl-pyranochromenes
Multicomponent reactions
Knoevenagel condensation
Michael addition
2009 Elsevier Ltd. All rights reserved.
Antioxidant and pro-oxidant activity
1. Introduction
efficient, allowing for the rapid, sometimes spectacular
generation of molecular complexity.10,11
Compounds bearing coumarin and pyrone moieties are
ubiquitous in a variety of important compounds and potent drugs
and present a wide variety of biological properties, such as anti-
inflammatory,1 anticoagulant,2 anti-angiogenesis,3 antimicrobial,4
antibacterial5 and antioxidant activity,6 and HIV protease
inhibitors.7
The issue of selectivity in multicomponent reactions is of
particular significance, due to the high probability of several
potential parallel reactions occur leading to different classes of
compounds.12 However, one of the most important objectives in
organic chemistry is to achieve the desired products in a chemo-
and regioselective way. Thus, many different process parameters
such as temperature, pressure, solvent, catalyst, among others can
be utilized to modulate the selectivity of synthetic
transformations.13
Multicomponent reactions (MCRs) are efficient and effective
methods in the sustainable and diversity-oriented synthesis of
compounds, and can be distinguished from the classical
sequential two-component chemistry synthetic process since it
combines in a one-pot three or more building blocks as the input
for product formation. They can use up to seven starting
components and often produce higher yields than classical two-
component reactions.8 They also provide a powerful tool for the
one-pot synthesis of diverse and complex compounds as well as
small and drug like heterocycles.9 But when two of these
components are identical, the processes are better described as
pseudo-multicomponent reaction. In the product of a pseudo-
MCR, the transformations resulting from the incorporation of
As part of our ongoing studies on the synthesis of bioactive
compounds,14-17 herein we report a pseudo-three-component
reaction of aromatic aldehydes with 4-hydroxy-6-methyl-2H-
pyran-2-one 1 by controlling their selectivity using different
catalysts (triethylamine, KF-Al2O3, HCl, H3PMo12O40,
H4SiMo12O40 and H2SO4-glycerin-carbon catalysts) and solvents
(ethanol, acetonitrile and toluene) that yielded two different
series of heterocyclic compounds.
Recent evidences suggest that free radicals, which are
generated in any bioorganic redox processes, may induce
two identical components have the advantage of being very
———
*
Corresponding authors: artur.silva@ua.pt (AMSS), prhamdi@gmail.com (MH), makhloufi_malika@yahoo.fr (MMC)

2
Tetrahedron
ACCEPTED MANUSCRIPT
oxidative damage in various components of the body (e.g.
this compound by a regioselective cascade reaction involving an
lipids, proteins and nucleic acids) and may also be involved in
processes leading to the formation of DNA mutations.
Furthermore, radical reactions play a significant role in the
development of life limiting chronic diseases, such as cancer,
hypertension, cardiac infarction, arteriosclerosis, rheumatism,
cataracts, among others.18
acid catalyzed Knoevenagel condensation of 1 with 2a leading to
compound 7, which undergoes a Michael addition in a specific
position of another molecule of TAL 1 affording intermediate 8.
An acid catalyzed cyclodehydration of 8 yielded the isolated
pyran-pyranochromene 4a (Scheme 3).
The reaction of salicylaldehyde 2a with TAL 1, used as a
model reaction, was studied in different solvents (acetonitrile,
toluene and ethanol) and using different acid catalysts
(H3PMo12O40, H4SiMo12O40, HCl, H2SO4-glycerin-carbon) (Table
1). Under all these acidic conditions this reaction afforded 10-(4-
hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-3-methyl-1H,10H-
pyrano[4,3-b]chromen-1-one (4a) as the only product. An
optimized yield of 47% was obtained in the presence of 5 mol%
of H3PMo12O40 in ethanol (Table 1, entry 1). The same reaction
under base-catalyzed conditions (triethylamine and KF-Al2O3
30%) afforded only the corresponding 3-acetoacetylcoumarin
(3a).
Antioxidants agents are molecules that can prevent cellular
damage caused by oxidation of other molecules. These agents
can be classified according to their mode of action as being free
radical terminators, chelators of metal ions involved in catalysing
lipid oxidation or oxygen scavengers that react with oxygen in
closed systems. A number of methods are available to assess the
free radical scavenging activity, but the assay using the stable
2,2-diphenyl-1-picrylhydrazyl radical (DPPH•) has received the
maximum attention owing to its ease of use and its
convenience.20-21 DPPH• scavenging is considered a good in vitro
model and is widely used to conveniently assess the antioxidant
efficacy of small molecules.22,23 In its radical form, DPPH• has an
absorbance at 517 nm which disappears when it is reduced by an
antioxidant molecule or a radical species to become the stable
diamagnetic
molecule
1,1 diphenyl 2 picrylhydrazine
(DPPH2). As a result, the color changes from purple to yellow.
This color change is taken as an indication of the hydrogen or
electron donating ability of the tested compounds. In the DPPH
assay, the antioxidant activity of a compound is evaluated
spectrophotometrically by monitoring the decrease in absorbance
at 517 nm.24,25 Herein we also report the evaluation of the
antiradical activity of the synthesized pyran-pyranochromene
derivatives 4a-k.
2. Results and Discussion
Scheme 2. Synthesis of 10-(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-3-
methyl-1H,10H-pyrano[4,3-b]chromen-1-ones 4a-k and 3,3'-[(2-hydroxy-3,4-
dimethoxyphenyl)methylene]bis(4-hydroxy-6-methyl-2H-pyran-2-one) (5).
2.1. Chemistry
In our previous study, we have shown that the condensation
of equimolar amounts of 4-hydroxy-6-methyl-2H-pyran-2-one
(TAL) 1 with salicylaldehyde derivatives 2, in refluxing toluene
and using triethylamine as an organocatalysts, afforded 3-
acetoacetylcoumarins 3 (Scheme 1).15
Scheme 1. Synthesis of 3-acetoacetylcoumarins 3.15
Scheme 3. Mechanism proposal for the synthesis of 10-(4-hydroxy-6-methyl-
2-oxo-2H-pyran-3-yl)-3-methyl-1H,10H-pyrano[4,3-b]chromen-1-ones 4a-k.
To investigate the catalytic properties of the heteropolyacid
(HPA) H3PMo12O40 in the Knoevenagel condensation of TAL,
we led react equimolar amounts of salicylaldehyde 2a with TAL
1, in refluxing ethanol and in the presence of 5 mol% of HPA. To
our surprise there is the formation of a product resulting from the
reaction of two molecules of TAL 1 and one of 2a, with the loss
of two water molecules (m/z 339 [M+H]+). These MS result
The pyran-pyranochromene 4a formation is sensitive to
nature of the solvent used and to the acid strength of the catalyst.
The best yields were obtained in the presence of a protic solvent
(ethanol) followed by toluene and then acetonitrile. The yield of
4a increases with the strength of the acid (heteropolyacid ˃
oxoacid) (Table 1). The formation of acetoacetylcoumarin 3a
requires a basic medium and seems to be independent of the
nature of solvent (protic or aprotic), being obtained in yields
ranging from 43 to 82%. It is noteworthy that the formation of
this compound 3a requires large amount of base compared to the
acid catalysts used for the formation of 4a (Table 1).
1
combined with some H NMR signals [11.61 (br s, 1H, OH-4’),
6.28 (q, J 0.7 Hz, 1H, H-5’), 5.98 (br s, 1H, H-4), 5.21 (s, 1H, H-
10), 2.21 (d, J 0.7, 3H, CH3-6’), 2.10 (s, 3H, CH3-3)] suggest the
formation of the interesting novel product 10-(4-hydroxy-6-
methyl-2-oxo-2H-pyran-3-yl)-3-methyl-1H,10H-pyrano[4,3-
b]chromen-1-one (4a), that was isolated in appreciate yield
(Scheme 2, entry 1 of table 1). One can explain the formation of

3
When the reaction was performed using two equiv of TAL 1
and one equiv of salicylaldehyde 2a in the presence of 5 mol% of
H3PMo12O40 in ethanol, pyran-pyranochromene 4a was obtained
in excellent yield (92%) (Table 2). Under these conditions the
yield of derivatives 4b and 4d have doubled and tripled,
respectively, compared with the conditions were equimolar
amounts of reagents were used. Subsequently, these optimized
conditions were applied for the conversion of 2-hydroxy-
naphthaldehyde 2d and various substituted salicylaldehydes 2e-l
into the corresponding fused pyranochromenes 4e-k and 5 (Table
2). Better yields have been obtained when using 5-
nitrosalicylaldehyde 2i and the unsubstituted salicylaldehyde 2a
(90% and 92%, respectively), followed by halo- 2h and 2j,
alkoxy- 2e-2f and 2k, 2l and hydroxy-salicylaldehydes 2b-2d,
being the worst yield (22.5%) obtained when using 4-
hydroxysalicylaldehyde 2c. These results seem indicate that
electron-withdrawing substituents of salicylaldehydes facilitate
the reaction and originate the product in better yields. The
reaction failed when using 3,5-di-t-butylsalicylaldehyde probably
due to steric hindrance caused by the two t-butyl substituents,
in clearly lower yields (up to 50%), together with the
ACCEPTED MANUSCRIPT
Knoevenagel products 3a-k (up to 66%) (Table 3). This can be
explained by the fact that the presence of water within the
catalyst H3PMo12O40 influences their physicochemical properties
such as acidity and the sorption capacity. Moreover, water also
competes with other polar molecules in the interception of free
protons.26
Table 2. Synthesis of 10-(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-3-
methyl-1H,10H-pyrano[4,3-b]chromen-1-ones 4a-k and 3,3'-[(2-hydroxy-3,4-
dimethoxyphenyl)methylene]bis(4-hydroxy-6-methyl-2H-pyran-2-one) (5) in
ethanol, catalyzed by H3PMo12O40 (5 mol%).a
TAL
Obtained
Yields
Entry
Aldehyde
b
(equiv)
compound
%
1
2
salicylaldehyde 2a
3-hydroxysalicylaldehyde 2b
4-hydroxysalicylaldehyde 2c
2-hydroxynaphthaldehyde 2d
salicylaldehyde 2a
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
2
4a
4b
4c
4d
4a
4b
4c
4d
4e
4f
47
28
17
31
92
81
22.5
66
75
79
77
85
90
84
77
76
3
4
5
6
3-hydroxysalicylaldehyde 2b
4-hydroxysalicylaldehyde 2c
2-hydroxynaphthaldehyde 2d
3-ethoxysalicylaldehyde 2e
4-methoxysalicylaldehyde 2f
3-methoxysalicylaldehyde 2g
5-bromosalicylaldehyde 2h
5-nitrosalicylaldehyde 2i
and gives the open structure
5
when using 3,4-
7
dimethoxysalicylaldehyde (2l). In the latter case the presence of
four consecutive substituents in the aldehyde moiety probable
prevent in final cyclodehydration and therefore we isolated the
8
9
10
11
12
13
14
15
16
open
form
3,3'-[(2-hydroxy-3,4-
4g
4h
4i
dimethoxyphenyl)methylene]bis(4-hydroxy-6-methyl-2H-pyran-
2-one) (5).
5-iodosalicylaldehyde 2j
4j
Table 1. Synthesis of acetoacetylcoumarin (3a) and 10-(4-hydroxy-6-methyl-
2-oxo-2H-pyran-3-yl)-3-methyl-1H,10H-pyrano[4,3-b]chromen-1-one (4a)
under different reaction conditions.a
3,4-dihydroxysalicylaldehyde 2k
3,4-dimethoxysalicylaldehyde 2l
4k
5
aReaction conditions: TAL 1, salicylaldehyde derivatives 2a-m, H3PMo12O40, refluxing
ethanol. bIsolated Yield
Obtained
Amount of
catalyst
Yields
(%)b
47
Entry
Solvents
Catalysts
compound
Table 3. Reactivity of salicylaldehyde derivatives 2 with TAL1 using water
as solvent and H3PMo12O40 (5 mol%) as catalyst.a
1
2
3
4a
4a
4a
ethanol
ethanol
ethanol
H3PMo12O40
H4SiMo12O40
HCl
5 mol%
5 mol%
38
1.2 equiv
31
Salicylaldehydes
Products 3
Yield %
Products 4
Yield %
H2SO4-glycerin
carbon
4
4a
ethanol
10% weight
25
2a
2b
2c
2d
2e
2f
3a
3b
3c
3d
3e
3f
52
12
10
10
62
44
66
60
45
50
60
4a
4b
4c
4d
4e
4f
37.5
50
15
33
28
22
10
24
50
18
20
5
6
7
8
9
3a
3a
4a
4a
4a
Ethanol
Ethanol
CH3CN
CH3CN
CH3CN
TEA
KF-Al2O3
H3PMo12O40
H4SiMo12O40
HCl
1 equiv
30% weight
5 mol%
65
55
<10
<10
10
5 mol%
1.2 equiv
2g
2h
2i
3g
3h
3i
4g
4h
4i
H2SO4-glycerin
carbon
10
4a
CH3CN
10% weight
<10
11
12
13
14
15
3a
3a
4a
4a
4a
CH3CN
CH3CN
Toluene
Toluene
Toluene
TEA
1 equiv
30% weight
5 mol%
43
82
2j
3j
4j
KF-Al2O3
H3PMo12O40
H4SiMo12O40
HCl
2k
3k
4k
21
aReaction conditions: TAL 1(2 equiv), salicylaldehydes 2 (1 equiv), H3PMo12O40 (5
5 mol%
18
1.2 equiv
<10
mol%), water (10 mL), 100°C.
H2SO4-glycerin
carbon
16
4a
Toluene
10% weight
21
The structural features of these two series of compounds 3a-k
and 4a-k were finely established based on 1D and 2D NMR
studies. The main features revealed in the 1H NMR spectra of 3a-
k are the presence of the ketoenol form in the acetoacetyl moiety,
the enol at δH 7.01 ppm (H-10) and 16.10 ppm (OH-9) and the
dione at 4.10-4.20 ppm (H-10). These assignments were
confirmed by their HSQC correlations with two different carbons
at δC 100.0-101.7 and 56.3-61.5 ppm, respectively. In addition
there is only one methyl group at δH 2.19-2.27 ppm (δC 18.7-27.7
ppm), and a singlet at δH 8.25-9.32 ppm corresponding to the
coumarinic H-4 (δC 133.9-151.0 ppm). The connectivities found
in the HMBC spectra allowed us to assign the quaternary carbon
resonances and to confirm the assignments of the protonated
carbons (Figure 1).
17
18
3a
3a
Toluene
Toluene
TEA
1 equiv
68
62
KF-Al2O3
30% weight
aReaction conditions: TAL 1 (1 equiv), salicylaldehyde 2a (1 equiv), catalyst, refluxing
solvent, bIsolated yields.
In order to obtain the fused pyranochromenes 4a-k by a green
method, we performed the reaction of salicylaldehyde derivatives
2a-k (1 equiv) with TAL 1 (2 equiv) using water as solvent, in
the presence of 5 mol% of H3PMo12O40 at 100°C. The advantage
of using HPAs under homogenous conditions lies in their high
solubility in polar solvent such as water and offer strong acidity.
Unfortunately, the reaction afforded the expected products 4a-k,

4
Tetrahedron
ACCEPTED MANUSCRIPT
1H NMR spectra of compounds 4a-k present two signals, a
hydroxy-6-methyl-2H-pyran-2-one) (5) is expressed comparing it
singlet and a doublet corresponding to 3 protons each, at δH 2.05-
2.12 and 2.18-2.24 ppm which were assigned to the protons of
CH3-3 and CH3-6’, respectively. The latter appears as a doublet
due to the coupling with H-5’, which appears as a quartet at δH
6.19-6.37 ppm. In the HMBC connectivities at room temperature
H-5’ correlates with C-3’, C-4’, C-6’ and C-7’, contrary to H-4,
that appears as a broad singlet at δH 5.95-6.04 ppm which
correlates only at 60°C with C-10a, C-4a, C-3 and C-11 (Figure
1) but doesn’t correlate with any carbons at room temperature.
Further characteristic singlet appears at δH 5.09-5.30 ppm (δC
25.2-27.9 ppm) due to the resonance of H-10. Finally, the
appearance of a hydroxy proton at δH 11.52-12.12 ppm (δC 161.0-
162.8) suggests the presence of the unique -OH and explains the
absence of the second pyrone hydroxy group. The connectivities
found in the HMBC spectra allowed us to confirm the
assignments of the protonated carbons and to assign the
remaining quaternary carbons of compounds 10-(4-hydroxy-6-
methyl-2-oxo-2H-pyran-3-yl)-3-methyl-1H,10H-pyrano[4,3-
b]chromen-1-ones 4a-k.
with that of the standard BHT (Figure 2). The analysis of figure 2
lead us to establish three groups of compounds: a) series I -
products weakly inhibiting DPPH•, 4a-d, 4h-j and 5; b) series II -
products presenting pro-oxidant activity, 4e-g; and c) series III -
product presenting antiradical and pro-oxidant activities, 4k.
From figure 3 it could be seen that compounds 4a-d, 4h-j and
5 showed weak to medium antiradicalar activity ranging from
11.1 to 51.6% for the highest concentration 30 mg mL-1, whereas
the standard BHT showed 99.6% inhibition. For these
compounds the highest scavenger activity was observed for
compound 5 and for pyranyl-pyranochromenes bearing a free
hydroxyl group 4b,c and for that arising from the 2-
hydroxynaphthaldeyde 4d. The order of activity regarding
substitution on chromene group for compounds 4 6-OH >
benzochromene > 8-OH > 8-NO2 > 8-I > 8-Br > H.
Figure 2. RSA (%) at 517 nm vs concentration of 4a-k, 5 and of the standard
BHT.
The presence of a catechol moiety [6,7-(OH)2] on the
chromone skeleton has completely changed the activity,
compound 4k behaves as the best antioxidant from the tested
compounds, at low concentration with maximum inhibition of
92.5% at the concentration of 1 mg mL-1 against 80% of BHT
with the same concentration. At higher concentration, this
compound becomes a pro-oxidant agent. The same occur with
compounds bearing alkoxy substituents 4e-g, possessing very
low inhibition (14%) at the concentration 5 mg mL-1 and then
presenting pro-oxidant activity.
Figure 1. HMBC connectivities of compounds 3h and 4h (60°C).
1
In the H and 13C NMR spectra 5 one can observe signals at
δH 8.41 (δC146.5 ppm) and 11.29 ppm (δC166.3 ppm) suggesting
the presence of phenolic and pyrone hydroxy groups, which
reveals that there was no intramolecular heterocyclisation. The
structure is symmetric, the two pyrones are equivalent (same
chemical shifts and doubled integrations in the 1H NMR
spectrum) and its molecular formula was confirmed by their mass
spectrum [M+Na]+ at m/z 439 and elemental analysis (see
experimental part).
The results of antioxidant screening were also depicted in
figure 3 at very low concentration (1 mg mL-1) for 4k and BHT.
This graph shows clearly that 4b and 5 are the best antioxidants
among compounds 4a-d, 4h-j and 5 although it present moderate
activity. On the other hand, 4k (92%) it is stronger antioxidant
than the standard (80%) at 1 mg mL-1.
2.2. Antioxidant Activity Assessment
The antioxidant activity (free radical scavenging activity) of
the synthesized 10-(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-
3-methyl-1H,10H-pyrano[4,3-b]chromen-1-ones 4a-k and 3,3'-
[(2-hydroxy-3,4-dimethoxyphenyl)methylene]bis(4-hydroxy-6-
methyl-2H-pyran-2-one) 5 was evaluated by the first time using
the 2,2-diphenyl-1-picrylhydrazyl free radical (DPPH•)
scavenging assay.22,23 Figure 2 shows the variation of absorbance
versus concentration of the different compounds 4a-k, 5 and of
the standard BHT. Lower the absorbance of the reaction mixture
indicates higher free radical scavenging activity. The capability
to scavenge the DPPH• (or inhibition %) was calculated as
follows:
RSA (%) = [(Ac –As)/Ac] x 100; where Ac is the absorbance
of the control (absorbance of DPPH• ethanol solution without
sample), and As is the absorbance of the tested compound after
60 min incubation.
Figure 3. RSA (%) values of compounds 4a-d, 4h-j and 5 at 30 mg mL-1 and
at 1 mg mL-1 for both 4k and BHT.
The antiradical activity of the pyranyl-pyranochromenes 4a-k
and of 3,3'-[(2-hydroxy-3,4-dimethoxyphenyl)methylene]bis(4-

5
Table 4 summarize the values of minimum inhibitory
concentrations IC50 of the tested compounds, being the most
significant those of 4k, 5, 4b and 4d (9.8 x 10-4, 7.9 x 10-2, 8.7 x
10-2 and 9.0 x 10-2 mol L-1, respectively), confirming 4k as the
best antioxidant agent.
mixture was stirred and refluxed until complete disappearance
ACCEPTED MANUSCRIPT
of the salicylaldehyde derivative 2a-k (monitoring by TLC). The
obtained solid was filtered off and washed with hot methanol and
were identified as compounds 4a-k and 5.
4.2.1. 10-(4-Hydroxy-6-methyl-2-oxo-2H-pyran-3-
yl)-3-methyl-1H,10H-pyrano[4,3-b]chromen-1-one
(4a)
Table 4. IC50 values of the antioxidant compounds tested (%)
Off-white solid, yield 1.55 g (92%); mp 269-271°C; 1H NMR
(DMSO-d6, 500 MHz): δ 11.61 (br s, 1H, OH-4’), 7.05-7.24 (m,
4H, H-6,7,8,9), 6.28 (q, J 0.7 Hz, 1H, H-5’), 5.98 (br s, 1H, H-4),
5.21 (s, 1H, H-10), 2.21 (d, J 0.7 Hz, 3H, CH3-6’), 2.10 (s, 3H,
CH3-3); 13C NMR (DMSO-d6, 126 MHz): δ 165.7 (C-1), 163.6
(C-2’), 162.5 (C-4’), 161.7 (C-6’), 161.7 (C-3), 161.6 (C-4a),
149.6 (C-5a), 129.0, 128.5, 125.4, 123.4 (C-9a), 116.3, 104.8 (C-
10a), 100.4 (C-4), 99.2 (C-5’), 98.0 (C-3’), 27.4 (C-10), 19.7
(CH3), 19.7 (CH3); MS (ESI+) m/z (%): 339 (25) [M+H]+, 361
(100), [M+Na]+, 699 (95) [2M+Na]+; C19H14O6 (338.31): Calcd.
C 67.45, H 4.17. Found C 67.55, H 4.19%.
Compound
IC50 (mg mL-1)
IC50 (mol L-1)
4a
4b
4c
190.1
30.9
5.6 x 10-1
8.7 x 10-2
1.3 x 10-1
9.0 x 10-2
5.9 x 10-1
2.3 x 10-1
5.2 x 10-1
9.8 x 10-4
7.9 x 10-2
1.6 x 10-4
46.8
4d
4h
4i
36.6
249.6
89.50
244.01
0.364
31.2
4j
4k
5
BHT
0.051
4.2.2. 6-Hydroxy-10-(4-hydroxy-6-methyl-2-oxo-2H-
pyran-3-yl)-3-methylpyrano[4,3-b]chromen-1(10H)-
one (4b)
3. Conclusions
Light-green solid, yield 1.43 g (81%); mp 275-277°C; 1H
NMR (DMSO-d6, 300 MHz): δ 11.60 (br s, 1H, OH-4’), 9.74 (br
s, 1H, OH-6), 6.81 (t, J 7.6 Hz, 1H, H-8), 6.68 (dd, J 7.6, 1.5 Hz,
1H, H-7), 6.50 (d, J 7.6 Hz, 1H, H-9), 6.19 (q, J 0.7 Hz, 1H, H-
5’), 5.95 (br s, 1H, H-4), 5.15 (s, 1H, H-10), 2.18 (d, J 0.7 Hz,
3H, CH3-6’), 2.07 (s, 3H, CH3-3); 13C NMR (DMSO-d6, 75
MHz): δ 165.3 (C-1), 162.9 (C-2’), 162.6 (C-4’), 161.8 (C-6’),
161.3 (C-3), 161.0 (C-4a), 157.0 (C-6), 145.0 (C-5a), 124.7 (C-
8), 124.0 (C-9), 118.4 (C-9a), 114.8 (C-7), 104.5 (C-10a), 100.2
(C-4), 99.1 (C-5’), 97.6 (C-3’), 27.2 (C-10), 19.5 (CH3), 19.5
(CH3); MS (ESI+) m/z (%): 355 (12) [M+H]+, 377 (95) [M+Na]+,
709 (8) [2M+H]+ 731 (100) [2M+Na]+; C19H14O7 (354.31):
Calcd. C 64.41, H 3.98. Found C 64.05, H 4.28%.
We have established a simple and efficient methodology to
control the selectivity of the reaction of salicylaldehyde
derivatives with 4-hydroxy-6-methyl-2H-pyran-2-one in different
solvents and using different catalysts. The optimal conditions
[ethanol as solvent and H3PMo12O40 (5 mol%) as catalyst]
allowed us to prepare novel 10-(4-hydroxy-6-methyl-2-oxo-2H-
pyran-3-yl)-3-methylpyrano[4,3-b]chromen-1(10H)-ones.
The
features of this procedure are mild reaction condition, good to
excellent yields, and operational simplicity.
From the antioxidant activity evaluation of the prepared
pyranyl-pyranochromene derivatives 4a-k and 5, one can
highlight that derivative 4k bearing a catechol group present the
higher activity at low concentration. At higher concentration it
became a pro-oxidant agent.
4.2.3. 7-Hydroxy-10-(4-hydroxy-6-methyl-2-oxo-2H-
pyran-3-yl)-3-methylpyrano[4,3-b]chromen-1(10H)-
one (4c)
4. Experimental section
1
Off-white solid, yield 399 mg (22.5%); mp 282-283°C; H
4.1. General
NMR (DMSO-d6, 300 MHz): δ 11.52 (br s, 1H, OH-4’), 9.66 (br
s, 1H, OH-7), 6.86 (d, J 8.4 Hz, 1H, H-9), 6.50 (dd, J 8.4, 2.4 Hz,
1H, H-8), 6.43 (d, J 2.4 Hz, 1H, H-6), 6.24(q, J 0.6 Hz, 1H, H-5’)
5.96 (br s, 1H, H-4), 5.09 (s, 1H, H-10), 2.19 (d, J 0.6 Hz, 3H,
CH3-6’), 2.08 (s, 3H, CH3-3); 13C NMR (DMSO-d6, 75 MHz): δ
165.0 (C-1), 163.4 (C-2’), 162.2 (C-4’), 161.2 (C-6’), 161.1 (C-
3), 161.0 (C-4a), 157.0 (COH-7), 149.7 (C-5a), 129.2 (C-9),
113.2 (C-9a), 112.7 (C-8), 104.6 (C-10a), 102.3 (C-6), 100.0 (C-
4), 98.8 (C-5’), 98.0 (C-3’), 26.4 (C-10), 19.3 (CH3), 19.3 (CH3);
MS (ESI+) m/z (%): 355 (15) [M+H]+, 377 (100) [M+Na]+, 731
(55) [2M+Na]+; C19H14O7 (354.31): Calcd. C 64.41, H 3.98.
Found C 64.52, H 4.00%.
Melting points were determined on a Stuart scientific SPM3
1
apparatus fitted with a microscope and are uncorrected. H and
13C NMR spectra were recorded in DMSO-d6 solutions on Bruker
1
Avance 300 (300.13 MHz for H and 75.47 MHz for 13C) and
500 (500.13 MHz for 1H and 125.77 MHz for 13C) spectrometers.
Chemical shifts are reported in parts per million (δ, ppm) using
TMS as internal reference, and coupling constants (J) are given
in Hertz (Hz). 13C assignments were made using HSQC, and
HMBC (delays for one bond and long-range JC/H couplings were
optimized for 145 and 7 Hz, respectively) experiments. Positive-
ion ESI mass spectra were acquired using a Q-TOF 2 instrument
[diluting 1 ꢀL of the sample chloroform solution ( 10-5 M) in
200 ꢀL of 0.1% trifluoroacetic acid/methanol solution. Nitrogen
was used as nebulizer gas and argon as collision gas. The needle
voltage was set at 3000 V, with the ion source at 80 °C and
desolvation temperature at 150 °C. Cone voltage was 35 V.
4.2.4. 12-(4-Hydroxy-6-methyl-2-oxo-2H-pyran-3-
yl)benzo[5,6-f] -3-methylpyrano[4,3-b] chromen-
1(10H)-one (4d)
1
Green solid, yield 1.28 g (66%); mp 308-310°C; H NMR
(DMSO-d6, 300 MHz): δ 12.12 (br s, 1H, OH-4’), 8.17 (d, J 8.0
Hz, 1H, H-11), 7.91 (dd, J 8.4, 1.1 Hz, 1H, H-8), 7.86 (d, J 8.4
Hz, 1H, H-7), 7.52 (t, J 8.4, 1.4 Hz, 1H, H-9), 7.45 (t, J 8.0, 1.1
Hz, 1H, H-10), 7.31 (d, J 8.4 Hz, 1H, H-6), 6.36 (q, J 0.7 Hz, 1H,
H-5’), 5.96 (s, 1H, H-4), 5.67 (s, 1H, H-12), 2.23 (d, J 0.7 Hz,
3H, CH3-6’), 2.02 (s, 3H, CH3-3); 13C NMR (DMSO-d6, 75
MHz): δ 164.0 (C-1), 162.1 (C-2’), 161.5 (COH-4’), 161.4 (C-
6’), 160.8 (C-3), 160.8 (C-4a), 147.9 (C-5a), 131.2 (C-11a),
130.8 (C-7a), 128.8 (C-8), 128.6 (C-7), 127.1 (C-10), 124.8 (C-
9), 123.0 (C-11), 116.8 (C-6), 114.8 (C-11b), 102.6 (C-12a),
4.2. General procedure for the synthesis of 10-(4-hydroxy-6-
methyl-2-oxo-2H-pyran-3-yl)-3-methylpyrano[4,3-b]chromen-
1(10H)-ones 4a-k and 3,3'-[(2-hydroxy-3,4-dimethoxyphenyl)
methylene]bis(4-hydroxy-6-methyl-2H-pyran-2-one) (5)
A dry flask was charged with 4-hydroxy-6-methyl-2H-pyran-
2-one1 [(1 equiv, 5 mmol) or (2 equiv, 0.1 mmol)], the
appropriate salicylaldehyde derivative 2a-k (1 equiv, 5 mmol)
and the catalyst (5 mol%, see table 1), in solvent (10 mL). The

6
Tetrahedron
100.0 (C-4), 98.5 (C-5’), 97.6 (C-3’), 25.2 (C-12), 19.3 (CH3),
(C-10), 19.1 (CH3), 19.0 (CH3); MS (ESI+) m/z (%): 439.0 (100)
ACCEPTED MANUSCRIPT
19.2 (CH3); MS (ESI+) m/z (%): 379 (13) [M+H]+, 411 (100)
[M+Na]+, 799 (40) [2M+Na]+; C23H16O6 (388.37): Calcd. C
71.13, H 4.15. Found C 71.32, H 4.17%.
[(M+Na)+, 79Br], 441.0 (95) [(M+Na)+, 81Br]; C19H13BrO6
(417.21): Calcd. C 54.70, H 3.14. Found C 54.45, H 3.14%.
4.2.9. 8-Nitro-10-(4-hydroxy-6-methyl-2-oxo-2H-
pyran-3-yl)-3-methylpyrano[4,3-b]chromen-1(10H)-
one (4i)
4.2.5. 6-Ethoxy-10-(4-hydroxy-6-methyl-2-oxo-2H-
pyran-3-yl)-3-methylpyrano[4,3-b]chromen-1(10H)-
one (4e)
Off-White solid, yield 1.72 g (90%); mp 335-337°C; 1H NMR
(DMSO-d6, 300 MHz): δ 11.97 (br s, 1H, OH-4’), 8.10 (dd, J 9.0,
2.7 Hz, 1H, H-7), 7.87 (d, J 2.7 Hz, 1H, H-9), 7.35 (d, J 9.0 Hz,
1H, H-6), 6.37 (q, J 0.6 Hz, 1H, H-5’), 6.04 (br s, 1H, H-4), 5.30
(s, 1H, H-10), 2.24 (d, J 0.6 Hz, 3H, CH3-6’), 2.12 (s, 3H, CH3-
3); 13C NMR (DMSO-d6, 126 MHz): δ 165.8 (C-1), 163.1 (C-2’),
162.1 (C-4’), 162.0 (C-6’), 161.7 (C-3), 159.2 (C-4a), 153.7 (C-
5a), 144.0 (C-8), 124.6 (C-9a), 124.2 (C-9), 123.9 (C-7), 117.4
(C-6), 103.8 (C-10a), 100.0 (C-4), 98.4 (C-5’), 98.1 (C-3’), 27.0
(C-10), 19.4 (CH3), 19.3 (CH3); MS (ESI+) m/z (%): 406.1 (100)
(M+Na)+, 407.1 (15); C19H13NO8 (383.31): Calcd. C 59.54, H
3.42. Found C 59.18, H 3.32%.
1
Purple solid, yield 1.43 g (75%); mp 253-256°C; H NMR
(DMSO-d6, 300 MHz): δ 11.60 (br s, 1H, OH-4’), 6.63 (d, J 7.8
Hz, 1H, H-7), 6.88 (dd, J 7.8, 1.3 Hz, 1H, H-9), 6.96 (t, J 7.8, Hz,
1H, H-8), 6.33 (q, J 0.5 Hz, 1H, H-5’), 5.97 (br s, 1H, H-4), 5.18
(s, 1H, H-10), 4.04 (q, J 7.0 Hz, 2H, OCH2-6), 2.21 (d, J 0.5 Hz,
3H, CH3-6’), 2.10 (s, 3H, CH3-3), 1.35 (t, J 7.0 Hz, 3H,
OCH2CH3-6); 13C NMR (DMSO-d6, 126 MHz): δ 164.9 (C-1),
163.0 (C-2’), 161.9 (C-4’), 160.9 (C-6’), 160.8 (C-3), 160.8 (C-
4a), 146.1 (C-5a), 139.2 (C-6), 124.4 (C-9a), 123.7 (C-8), 119.7
(C-9), 112.4 (C-7), 104.2 (C-10a), 99.8 (C-4), 98.6 (C-5’), 97.4
(C-3’), 64.4 (OCH2-6), 27.0 (C-10), 19.0 (CH3), 18.9 (CH3), 14.4
(CH3-6); MS (ESI+) m/z (%): 405.2 (100) [M+Na]+, 787.2 (25)
[2M+Na]+; C21H18O7 (382.36): Calcd. C 65.96, H 4.74. Found C
66.13, H 4.64%.
4.2.10. 8-Iodo-10-(4-hydroxy-6-methyl-2-oxo-2H-
pyran-3-yl)-3-methylpyrano[4,3-b]chromen-1(10H)-
one (4j)
1
4.2.6. 7-Methoxy-10-(4-hydroxy-6-methyl-2-oxo-2H-
pyran-3-yl)-3-methylpyrano[4,3-b]chromen-1(10H)-
one (4f)
Off-white solid, yield 1.95 g (84%); mp 300-304°C; H NMR
(DMSO-d6, 300 MHz): δ 11.77 (br s, 1H, OH-4’), 7.53 (dd, J 8.6,
1.9 Hz, 1H, H-7), 7.32 (d, J 1.9 Hz, 1H, H-9), 6.91 (d, J 8.6 Hz,
1H, H-6), 6.27 (q, J 0.6 Hz, 1H, H-5’), 6.00 (br s, 1H, H-4), 5.17
(s, 1H, H-10), 2.20 (d, J 0.6 Hz, 3H, CH3-6’), 2.11 (s, 3H, CH3-
3); 13C NMR (DMSO-d6, 75 MHz): δ 165.9 (C-1), 162.3 (C-2’),
162.0 (C-4’), 162.0(C-6’), 161.9 (C-3), 161.3 (C-4a), 149.6 (C-
5a), 137.1 (C-9), 137.0 (C-7), 126.2 (C-9a), 118.9 (C-6), 104.5
(C-10a), 100.4 (C-4), 99.0 (C-5’), 97.9 (C-3’), 88.8 (C-8), 27.1
(C-10), 19.8 (CH3), 19.7 (CH3); MS (ESI+) m/z (%) 487.0 (100)
(M+Na)+, 488.0 (15) (M+Na)+; C19H13IO6 (463.98): Calcd. C
49.16, H 2.82. Found C 49.16, H 2.82%.
1
Black solid, yield 1.45 g (79%); mp 223-225°C; H NMR
(DMSO-d6, 300 MHz): δ 11.58 (br s, 1H, OH-4’), 6.99 (d, J 8.5
Hz, 1H, H-9), 6.68 (dd, J 8.5, 2.6 Hz, 1H, H-8), 6.64 (d, J 2.6 Hz,
1H, H-6), 6.25 (q, J 0.7 Hz, 1H, H-5’), 5.97 (br s, 1H, H-4), 5.13
(s, 1H, H-10), 3.74 (s, 3H, OCH3-7), 2.21 (d, J 0.7 Hz, 3H, CH3-
6’), 2.10 (s, 3H, CH3-3); 13C NMR (DMSO-d6, 75 MHz): δ 166.1
(C-1), 163.2 (C-2’), 162.1 (C-4’), 162.0 (C-6’), 161.9 (C-3),
161.8 (C-4a), 159.5 (C-7), 150.3 (C-5a), 129.8 (C-9), 115.2 (C-
9a), 112.2 (C-8), 104.9 (C-10a), 101.5 (C-6), 100.6 (C-4), 99.4
(C-5’), 98.5 (C-3’), 56.0 (OCH3-7), 27.0 (C-10), 19.9 (CH3), 19.8
(CH3); MS (ESI+) m/z (%): 391.1 (100) [M+Na]+; C20H16O7
(368.34): Calcd. C 65.22, H 4.38. Found C 65.20, H 4.37%.
4.2.11. 6,7-Dihydroxy-10-(4-hydroxy-6-methyl-2-
oxo-2H-pyran-3-yl)-3-methylpyrano[4,3-b] chromen-
1(10H)-one (4k)
1
4.2.7. 6-Methoxy-10-(4-hydroxy-6-methyl-2-oxo-2H-
pyran-3-yl)-3-methylpyrano[4,3-b]chromen-1(10H)-
one (4g)
Black solid, yield 1.42 g (77%); mp 318-320°C; H NMR
(DMSO-d6, 500 MHz): δ 11.45 (br s, 1H, OH-4’), 9.20 (br s, 1H,
OH), 8.80 (br s, 1H, OH), 6.50 (d, J 8.4 Hz, 1H, H-8), 6.36 (d, J
8.4 Hz, 1H, H-9), 6.23 (q, J 0.6 Hz, 1H, H-5’), 5.96 (s, 1H, H-4),
5.10 (s, 1H, H-10), 2.21 (d, J 0.6 Hz, 3H, CH3-6’), 2.10 (s, 3H,
CH3-3); 13C NMR (DMSO-d6, 126 MHz): δ 164.8 (C-1), 162.2
(C-2’), 161.0 (C-4’), 160.9 (C-6’), 160.8 (C-3), 159.2 (C-4a),
145.0 (C-5a), 138.8 (C-7), 132.8 (C-6), 117.2 (C-9), 114.2 (C-
9a), 111.9 (C-8), 101.2 (C-10a), 100.0 (C-4), 98.9 (C-5’), 98.3
(C-3’), 26.8 (C-10), 19.3 (CH3), 19.3 (CH3); MS (ESI+) m/z (%):
353.3 (100) [M-H2O+H]+, 393.2 (76) [M+Na]+; C19H14O8
(370.31): Calcd. C 61.62, H 3.81. Found C 61.64, H 3.81%.
Light-purple solid, yield 1.41 g (77%); mp 273-274°C;1H
NMR (DMSO-d6, 500 MHz): δ 11.63 (br s, 1H, OH-4’), 7.01 (t, J
7.5 Hz, 1H, H-8), 6.90 (dd, J 7.5, 1.2 Hz, 1H, H-7), 6.63 (d, J 7.5
Hz, 1H, H-9), 6.32 (q, J 0.8 Hz, 1H, H-5’), 5.97 (s, 1H, H-4),
5.18 (s, 1H, H-10), 3.82 (s, 3H, OCH3-12), 2.20 (d, J 0.8 Hz, 3H,
CH3-6’), 2.08 (s, 3H, CH3-3); 13C NMR (DMSO-d6, 126 MHz): δ
165.2 (C-1), 162.1 (C-2’), 161.2 (C-4’), 161.1 (C-6’), 161.0 (C-
3), 160.8 (C-4a), 147.0 (C-5a), 138.7 (C-6), 124.7 (C-8), 123.6
(C-9a), 119.7 (C-9), 110.7 (C-7), 103.7 (C-10a), 99.8 (C-4), 98.8
(C-5’), 97.0 (C-3’), 55.7 (OCH3-6), 27.0 (C-10), 19.3 (CH3),
19.3(CH3); MS (ESI+) m/z (%): 391.1 (100) [M+Na]+, 759.3 (37)
[2M+Na]+; C20H16O7 (368.34): Calcd. C 65.22, H 4.38. Found C
65.24, H 4.37%.
4.2.12. 4-Hydroxy-3-((2-hydroxy-3,4-
dimethoxyphenyl)(4-hydroxy-6-methyl-2-oxo-2H-
pyran-3-yl)methyl)-6-methyl-2H-pyran-2-one (5)
Grey solid, yield 1.51 g (76%); mp 256-257°C; 1H NMR
(DMSO-d6, 300 MHz): δ 11.29 (br s, 2H, OH-4,4’), 8.41 (br s,
1H, OH-2”), 6.56 (d, J 8.7 Hz, 1H, H-6”), 6.40 (dd, J 8.6, 0.7 Hz,
1H, H-5”), 6.03 (q, J 0.8 Hz, 2H, H-5,5’), 5.89 (s, 1H, H-7), 3.73
(s, 3H, OCH3), 3.53 (s, 3H, OCH3), 2.17 (s, 6H, CH3-6,6’); 13C
NMR (DMSO-d6, 75 MHz): δ 167.5 (C-2,2’), 166.3 (C-4,4’),
161.0 (C-6,6’), 147.9 (C-4”), 146.5 (C-2”), 139.5 (C-3”), 126.4
(C-6”), 117.9 (C-1”), 106.7 (C-5”), 102.8 (C-5,5’), 101.6 (C-
3,3’), 59.6 (OCH3), 56.3 (OCH3), 30.7 (C-7), 19.5 (CH3-6,6’);
MS (ESI+) m/z (%): 439.3 (100) [M+Na]+, 353.4 (85) [M-
2CH3OH+H]+; C21H20O9 (416.38): Calcd. C 60.58, H 4.84. Found
C 60.64, H 4.83%.
4.2.8. 8-Bromo-10-(4-hydroxy-6-methyl-2-oxo-2H-
pyran-3-yl)-3-methylpyrano[4,3-b]chromen-1(10H)-
one (4h)
Off-White solid, yield 1.77 g (85%); mp 302-303°C; 1H NMR
(DMSO-d6, 500 MHz): δ 11.77 (br s, 1H, OH-4’), 7.37 (dd, J 8.7,
2.3 Hz, 1H, H-7), 7.19 (d, J 2.3 Hz, 1H, H-9), 7.06 (d, J 8.7 Hz,
1H, H-6), 6.25 (q, J 0.6 Hz, 1H, H-5’), 5.99 (s, 1H, H-4), 5.22 (s,
1H, H-10), 2.21 (d, J 0.6 Hz, 3H, CH3-6’), 2.12 (s, 3H,CH3-3);
13C NMR (DMSO-d6, 126 MHz): δ 165.2(C-1), 162.9 (C-2’),
161.6 (C-4’), 161.3 (C-6’), 161.2 (C-3), 160.6 (C-4a), 148.4 (C-
5a), 130.6 (C-7), 130.4 (C-9), 125.5 (C-9a), 118.0 (C-6), 115.9
(C-8), 103.7 (C-10a), 99.8 (C-4), 98.3 (C-5’), 97.2(C-3’), 26.9

7
m/z (%): 331.0 (100) [(M+Na)+, 79Br], 333.0 (95) [(M+Na)+,
4.3. General procedure for the synthesis of 3-acetoacetyl-
coumarins 3a-k (table 3)
ACCEPTED MANUSCRIPT
81Br]; C13H9BrO4 (309.12): Calcd. C 50.51, H 2.93. Found C
50.12, H 2.95%.
A mixture of 4-hydroxy-6-methyl-2H-pyran-2-one 1 (2 equiv,
0.1 mmol), the appropriate salicylaldehyde derivative 2a-k (1
equiv, 5 mmol) and 5 mol% of H3PMo12O40 in water (10 mL)
was stirred and refluxed for the appropriate time (see table 3).
The reaction completion was controlled by thin layer
chromatography (TLC); then the obtained solid was filtrated and
washed with hot methanol for give compounds 4a-k and the
filtrate afforded us the products 3a-k after extraction with
dichloromethane.
4.3.5. 3-Acetoacetyl-6-nitrocoumarin (3i)
1
Yellow solid, yield 620 mg (45%); mp 210-211°C; H NMR
(DMSO-d6, 300 MHz): δ 15.93 (br s, 1H, OH-9), 8.99 (s, 1H, H-
4), 8.98 (d, J 2.9 Hz, 1H, H-5), 8.50 (dd, J 9.2, 2.9 Hz, 1H, H-7),
7.68 (d, J 9.2 Hz, 1H, H-8), 6.88 (s, 1H, H-10 enol), 4.19 (s, 2H,
H-10), 2.24 (s, 3H, H-12); 13C NMR (DMSO-d6, 75 MHz): δ
203.2 (C-11 dione), 200.1 (C-11 enol), 191.9 (C-9 dione), 172.4
(C-9 enol), 157.8 (C-2), 157.0 (C-8a), 147.2 (C-6), 145.4 (C-3),
144.2 (C-4), 128.9 (C-4a), 126.6 (C-8), 119.2 (C-5), 118.1 (C-7),
101.9 (C-10 enol), 56.8 (C-10 dione), 27.7 (C-12); MS (ESI+)
m/z (%): 298.1 (75) (M+Na)+, 299.1 (10), 283.1 (100) (M+Na-
CH3)+, 284.1 (15); C13H9NO6 (275.22): Calcd. C 56.73, H 3.30.
Found C 56.72, H 3.31%.
Compounds 3a-d showed identical spectroscopic and
analytical data to those described in the literature.15
4.3.1. 3-Acetoacetyl-8-ethoxycoumarin (3e)
1
Black solid, yield 850 mg (62%); mp 260-261°C; H NMR
(DMSO-d6, 300 MHz): δ 15.99 (br s, 1H, OH-9), 8.78 (s, 1H, H-
9), 7.47 (d, J 8.0 Hz, 1H, H-5), 7.39 (d, J 8.0 Hz, 1H, H-7), 7.32
(t, J 8.0 Hz, 1H, H-6), 6.91 (s, 1H, H-10 enol), 4.17 (q, J 6.9 Hz,
2H, H-13), 4.15 (s, 2H, H-10), 2.25 (s, 3H, H-12), 1.38 (t, J 6.9
Hz, 3H, H-14); 13C NMR (DMSO-d6, 126 MHz): δ 203.4 (C-11
dione), 199.3 (C-11 enol), 191.9 (C-9 dione), 172.9 (C-9 enol),
157.2 (C-2), 148.2 (C-3), 146.4 (C-8), 145.5 (C-4), 143.4 (C-8a),
125.0 (C-6), 121.3 (C-5), 119.0 (C-4a), 117.2 (C-7), 101.1 (C-10
enol), 56.5 (C-10 dione), 64.5 (C-13), 27.1 (C-12), 14.6 (C-14);
MS (ESI+) m/z (%): 297.1 (100) [M+Na]+; C15H14O5 (274.08):
Calcd. C 65.59, H 5.15. Found C 65.20, H 5.02%.
4.3.6. 3-Acetoacetyl-6-iodocoumarin (3j)
1
Yellow solid, yield 890 mg (50%); mp 219-220°C; H NMR
(DMSO-d6, 300 MHz): δ 15.85 (br s, 1H, OH-9), 8.77 (s, 1H, H-
4), 8.38 (d, J 2.1 Hz, 1H, H-5), 8.02 (dd, J 8.7, 2.1 Hz, 1H, H-7),
7.29 (d, J 8.7 Hz, 1H, H-8), 6.89 (s, 1H, H-10 enol), 4.16 (s, 2H,
H-10), 2.21 (s, 3H, H-12); 13C NMR (DMSO-d6, 75 MHz): δ
202.9 (C-11 dione), 199.9 (C-11 enol), 191.6 (C-9 dione), 172.9
(C-9 enol), 157.4 (C-2), 154.0 (C-8a), 147.0 (C-3), 145.1 (C-4),
142.7 (C-7), 138.6 (C-5), 121.0 (C-8), 118.8 (C-4a), 101.7 (C-10
enol), 89.1 (C-6), 56.9 (C-10 dione), 27.6 (C-12); MS (ESI+) m/z
(%): 379.0 (100) (M+Na)+, 381.4 (28); C13H9IO4 (356.12): Calcd.
C 43.85, H 2.55. Found C 43.72, H 2.55%.
4.3.2. 3-Acetoacetyl-7-methoxycoumarin (3f)
1
Black solid, yield 570 mg (44%); mp 194-195°C; H NMR
4.3.7. 3-Acetoacetyl-7,8-dihydroxycoumarin (3k)
(DMSO-d6, 300 MHz): δ 16.10 (br s, 1H, OH-9),8.80 (s, 1H, H-
4), 7.92 (d, J 8.7 Hz, 1H, H-5), 7.08 (d, J 2.4 Hz, 1H, H-8), 7.06
(dd, J 8.7, 2.4 Hz, 1H, H-6), 6.89 (s, 1H, H-10 enol), 4.13 (s, 2H,
H-10), 3.91 (s, 3H, H-13), 2.23 (s, 3H, H-12); 13C NMR (DMSO-
d6, 126 MHz): δ 203.5 (C-11 dione), 198.1 (C-11 enol), 191.5 (C-
9 dione), 174.4 (C-9 enol), 164.9 (C-7), 157.8 (C-2), 156.5 (C-
8a), 148.4 (C-3), 146.5 (C-4), 131.9 (C-5), 115.7 (C-4a), 113.6
(C-8), 112.1 (C-6), 100.3 (C-10 enol), 56.4 (C-10 dione), 56.4
(C-13), 26.8 (C-12); MS (ESI+) m/z (%): 283.1 (100) [M+Na]+;
C15H14O5 (260.07): Calcd. C 64.61, H 4.65. Found C 64.67, H
4.68%.
1
Yellow solid, yield 780 mg (60%); mp 260-262°C; H NMR
(DMSO-d6, 300 MHz): δ 16.24 (br s, 1H, OH-9), 10.04 (br s, 2H,
OH-7,8), 8.66 (s, 1H, H-4), 7.28 (d, J 8.2 Hz, 1H, H-5), 6.88 (d, J
8.2 Hz, 1H, H-6), 6.85 (s, 1H, H-10 enol), 4.10 (s, 2H, H-10
dione), 2.19 (s, 3H, H-12); 13C NMR (DMSO-d6, 75 MHz): δ
184.3 (C-11 dione), 177.4 (C-11 enol), 177.05 (C-9 dione), 174.4
(C-9 enol), 167.9 (COH-7), 167.5 (COH-8), 160.0 (C-2), 154.5
(C-8a), 154.2 (C-3), 151.0 (C-4), 126.7 (C-5), 113.5 (C-4a),
111.8 (C-6), 82.7 (C-10 enol), 61.5 (C-10 dione), 23.5 (C-12);
MS (ESI+) m/z (%): 285.1 (100) [M+Na]+; C13H10O6 (262.05):
Calcd. C 59.55, H 3.84. Found C 59.63, H 3.86%.
4.3.3. 3-Acetoacetyl-8-methoxycoumarin (3g)
4.4. Evaluation of the Antiradicalar Evaluation of Pyranyl-
pyranochromene derivatives 4a-k
1
Dark red solid, yield 850 mg (66%); mp 170-171°C; H NMR
(DMSO-d6, 500 MHz): δ 16.00 (br s, 1H, OH-9), 8.78 (s, 1H, H-
4), 7.48 (d, J 8.0, 1.2 Hz, 1H, H-5), 7.42 (d, J 8.0, 1.2 Hz, 1H, H-
7), 7.34 (t, J 8.0 Hz, 1H, H-6), 6.90 (s, 1H, H-10 enol), 4.16 (s,
2H, H-10), 3.92 (s, 3H, H-13), 2.22 (s, 3H, H-12); 13C NMR
(DMSO-d6, 75 MHz): δ 203.5 (C-11 dione), 199.3 (C-11 enol),
191.9 (C-9 dione), 172.9 (C-9 enol), 157.2 (C-2), 148.2 (C-3),
146.4 (C-8), 146.2 (C-4), 143.3 (C-8a), 125.0 (C-6), 121.3 (C-5),
118.9 (C-4a), 116.4 (C-7), 101.1 (C-10 dione), 56.3 (C-10 enol),
56.2 (C-13), 27.1 (C-12); MS (ESI+) m/z (%): 283.1 (100)
[M+Na]+; C13H10O4 (283.24): Calcd. C 64.61, H 4.65. Found C
64.52, H 4.51%.
The DPPH radical scavenging capacity of the obtained
pyranyl-pyranochromene derivatives 4a-k and 5 was measured
from the bleaching of purple coloured ethanol solution of DPPH•.
The method described by Brand-Williams et al.23 DPPH• solution
was prepared by dissolving DPPH• in ethanol to give a
concentration of 4 mg 100 mL-1. Compounds 4a-k and 5 were
dissolved in DMSO to obtain a solution of 30 mg mL-1. The
concentration of test compounds was diluted with DMSO to get
final concentrations of 20, 10 and 5 mg mL-1 for all the
compounds, but both compound 4k and the standard were further
diluted to give concentration solutions of 1.5 x 10-1, 1 x 10-1, 5 x
10-2, 2.5 x 10-3, 1 x 10-3 mg mL-1. 40 µL of each tested
concentration of each compound was added to each well
separately in triplicate, and then 2 mL of DPPH solution was
added. Negative control wells were loaded with 40 µL of DMSO
and 2 mL of DPPH• solution each. After vortexing, the mixtures
were incubated at room temperature for 1 h in darkness at 25°C,
and then the absorbance of these compounds at different
concentrations was recorded at 517 nm. Butylated
hydroxytoluene (BHT) was used as standard for the antioxidant
activity screening. A blank containing only ethanol with DMSO
4.3.4. 3-Acetoacetyl-6-bromocoumarin (3h)
1
Yellow solid, yield 920 mg (60%); mp 211-212°C; H NMR
(DMSO-d6, 500 MHz): δ 16.00 (br s, 1H, OH-9), 8.79 (s, 1H, H-
4), 8.25 (d, J 2.0 Hz, 1H, H-5), 7.88 (dd, J 8.4, 2.0 Hz, 1H, H-7),
7.46 (d, J 8.4 Hz, 1H, H-8), 6.90 (s, 1H, H-10 enol), 4.17 (s, 2H,
H-10), 2.26 (s, 3H, H-12); 13C NMR (DMSO-d6, 126 MHz): δ
203.2 (C-11 dione), 199.5 (C-11 enol), 191.7 (C-9 dione), 172.4
(C-9 enol), 157.0 (C-2), 153.0 (C-8a), 146.5 (C-3), 144.8 (C-4),
136.6 (C-7), 132.2 (C-5), 120.3 (C-6), 118.4 (C-8), 116.5 (C-4a),
101.3 (C-10 enol), 56.4 (C-10 dione), 27.2 (C-12); MS (ESI+)

8
Tetrahedron
ACCEPTED MANUSCRIPT
11. (a) Cai, Q.; Jia, F.-C.; Li, D.-K.; Xu, C.; Ding, K.-R.; Wu, A.-X.
was used as the control. Each measurement was performed in
Tetrahedron 2015, 71, 6104-6111. (b) Jagadishbabu, N.; Shivashankar,
K. J. Heterocycl. Chem. 2017, 54, 1543-1549.
triplicate.
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Acknowledgments
Thanks are due to University of Aveiro and FCT/MEC for the
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5416-5470; (b) Laschat, S.; Becheanu, A.; Bell, T.; Baro, A. Synlett
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financial
support
of
the
QOPNA
research
unit
(FCTUID/QUI/00062/2013) through national founds and, where
applicable, co-financed by the FEDER, within the PT2020
Partnership Agreement, and to the Portuguese NMR Network.
We would like to thank the Ministry of Higher Education and
Scientific Research of Algeria for awarding an exchange
scholarship.
15. Makhloufi-Chebli, M.; Hamdi, M.; Silva, A. M. S.; Balegroune. F. J.
Soc. Alger. Chim. 2008, 18, 91-101.
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Supplementary Material
Supplementary data related to this article can be found at
https://doi.org/......
10. Castillo, J.-C.; Quiroga, J.; Abonia, R.; Rodriguez, J.; Coquerel, Y. J.
Org. Chem. 2015, 80, 9767–9773.
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