H5BW12O40 as a green and efficient homogeneous but recyclable catalyst in the synthesis of 4H-Pyrans via multicomponent reaction

Article abstract of DOI:10.1002/aoc.4479

Keggin-type heteropolyacid, H₅BW₁₂O₄₀ (BWA) with a higher negative charge and stronger Br?nsted acidity comparing to Si and P derivatives was used as an efficient, green, and reusable catalyst in a three-component reaction

Full text of DOI:10.1002/aoc.4479

Received: 2 April 2018
DOI: 10.1002/aoc.4479
Revised: 25 May 2018
Accepted: 28 May 2018
F U L L P A P E R
H5BW12O40 as a green and efficient homogeneous but
recyclable catalyst in the synthesis of 4H‐Pyrans via
multicomponent reaction
Majid M. Heravi1
| Masoud Mirzaei2
| Seyed Yahya Shirazi Beheshtiha1 |
Vahideh Zadsirjan1 | Fatemeh Mashayekh Ameli1 | Maryam Bazargan2
1 Department of Chemistry, School of
Keggin‐type heteropolyacid, H5BW12O40 (BWA) with a higher negative charge
Science, Alzahra University, PO Box
1993891176, Vanak, Tehran, Iran
2 Department of Chemistry, Faculty of
Science, Ferdowsi University of Mashhad,
917751436, Mashhad, Iran
and stronger Brønsted acidity comparing to Si and P derivatives was used as an
efficient, green, and reusable catalyst in a three‐component reaction involving
the cyclocondensation of various β‐dicarbonyl compounds, differently
substituted aromatic aldehydes and malononitrile in EtOH/H2O for the facile,
clean, and high yielding synthesis of 4H‐pyrans. All reactions were completed
in short times and the products were obtained in good to excellent yields. The
reaction medium could be recycled and reused several times without any loss
of efficiency.
Correspondence
Majid M. Heravi and Vahideh Zadsirjan,
Department of Chemistry, School of
Science, Alzahra University, PO Box
1993891176, Vanak, Tehran, Iran.
Email: mmh1331@yahoo.com;
mmheravi@alzahra.ac.ir
KEYWORDS
Masoud Mirzaei and Maryam Bazargan,
Department of Chemistry, Faculty of
Science, Ferdowsi University of Mashhad,
917751436, Mashhad, Iran
H5BW12O40, homogeneous catalysis, Keggin‐type polyoxometalates, multicomponent reaction, one‐
pot synthesis
Email: mirzaeesh@um.ac.ir;
Maryam_bazargan2000@yahoo.com
Funding information
Alzahra University; Iran National Science
Foundation (INSF); Ferdowsi University
of Mashhad, Mashhad, Iran, Grant/Award
Number: 3/42202
1 | INTRODUCTION
of their multiple active sites, including protons, oxygen
atoms, and metals; i) protons can act as Brønsted acids
Nowadays, the design of active, selective, environmen-
tally benign, and recyclable heterogeneous catalysts that
have a major impact on industrial applications is a main
purpose of the modern synthetic chemistry. Polyoxo-
metalates (POMs) are composed of cations and polyanion
clusters with unique properties that are the interesting
field for researchers. These species have been known for
almost two centuries and they have attracted much inter-
est because of their applications in broad fields such as
catalysis, sensing[1] magnetism,[2] medicine[3] and so on.
In fact, POMs can be viewed as versatile catalysts because
to promote acid‐catalyzed reactions. ii) Some oxygen
atoms on the surface of POM anions with a high negative
charge are basic enough to react with protons, even to
abstract active protons from organic substrates. Accord-
ingly, these surface oxygen atoms of POM catalysts can be
the active sites in base‐catalyzed reactions. iii) The metal
ions on the skeleton of polyamines possess unoccupied
orbitals that can accept electrons. In this way, polyamines
can also act as Lewis acids.[4] Among the many types of
POMs, Keggin‐type structures are widely investigated for
catalyzed reactions due to their suitable sizes, more stable
Appl Organometal Chem. 2018;e4479.
wileyonlinelibrary.com/journal/aoc
© 2018 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4479

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HERAVI ET AL.
structures and low prices.[5] Keggin compounds as a com-
mon and important class of POMs have the general formula
HnXM12O40 where X is heteroatom (P, Si, As, Ge, B) and M
is the addenda such as Mo or W.[6] Typically, they are
water‐soluble and form Keggin anions [XM12O40]n– and
hydrated protons which are mobile in nature like H+,
The use of safe and inexpensive solvents along with
heterogeneous and recyclable catalysts is the most serious
concerns in green chemistry.[9] Thus, aqua mediated
reactions are one of desirable and attractive selection in
organic synthesis because of keeping the environment
clean and safe. For these reasons water as the most abun-
dant and non‐toxic molecule in nature and being virtually
free of cost is an ideal solvent in chemical reactions.[11]
Pyrans are significant moieties in several naturally
occurring compounds[12] as well as photochromic mate-
rials.[13] Compounds containing a pyran unit exhibit sev-
eral biological properties and play vital roles in biological
processes.[13] In addition, 4H‐pyrans are beneficial interme-
diates for the synthesis of wide verity of heterocyclic sys-
tems, such as pyranopyridine derivatives,[14] pyrano[2]
pyrimidines[15] and pyridine‐2‐ones.[16] Thus, preparation
of this heterocyclic core has extended high reputation in
heterocyclic chemistry. Several strategies have been
reported for the synthesis of pyrans, mostly via a three‐
component reaction involving the cyclocondesation of var-
ious β‐dicarbonyl compounds, differently substituted aro-
matic aldehydes and alkylmalonates.[17] This MCR have
been catalyzed with a wide range of catalytic systems such
as MgO,[18] (S)‐proline,[19] SiO2 nanoparticles,[20]
hexadecyltrimethyl ammonium bromide (HMTAB),[21]
rare earth perfluorooctanoate (RE (PFO)3),[22] silica
bonded n‐propyl‐4‐aza‐1‐azonia bicycle [2,2,2] octane
chloride (SB‐DABCO),[23] amino functionalized ionic
liquids,[17,24] magnetic iron oxide supported phenylsulfonic
acid (Fe3O4@Ph‐SO3H),[25] nano‐SiO2,[26] HPA‐dendrimer-
functionalized magnetic nanoparticles (Fe3O4@D‐NH2‐
HPA),[27] a mixed‐ligand Cu (II) Schiff base complex,[28]
amine‐functionalized hyper‐crosslinked polyphenanthrene
as a metal‐free catalyst,[29] bis (4‐pyridylamino) triazine sta-
bilized on silica‐coated nano‐Fe3O4 particles,[30] polypyr-
role/Fe3O4/CNT,[31] polystyrene‐supported DABCO ionic
liquid ([P‐DABCO]Cl),[32] 12‐molybdophosphoric acid
encapsulated in the nanocavities of modified dealuminated
zeolite Y (MDAZY),[33] and magnetically nanomaterial
consisting of dihydrogen phosphate ions supported on sil-
ica‐coated magnetite nanoparticle (magnetite‐dihydrogen
phosphate)[34] which each of them has its merits and short-
comings. Therefore, development of an efficient, MCR with
chemoselective as well as being performed under heteroge-
neous catalysis and green conditions for the synthesis of 4H‐
pyrans is still in much demand.
H3O+, H5O2 and etc. (‘Called as Heteropoly Acids
+
(HPAs)’). It is well known that the anionic part of HPAs
can stabilize the cationic organic intermediates[7] thereby
promoting the catalytic reactions.
The H5BW12O40 (BWA) Keggin‐type structures carry
higher negative charge comparing to H4SiW12O40 (SiW)
and H3PW12O40 (PW) affording stronger Brønsted acid,
however, this HPA is rarely explored as a catalyst in organic
transformation in spite of its easy preparation methods. In
order to see the role of the above three types of HPAs in
the formation of new compounds we ran a Cambridge
Structural Database (CSD) analysis (CSD, Version 5.38
updates May 2017). A survey revealed that number of the
synthesized compounds of BWA is significantly less than
SiWA and PWA ones (Figure 1).[8] Therefore, these advan-
tages encouraged us to explore the critical role of BWA as a
Brønsted acid catalyst which can be further expanded to the
synthesis of the variety of organic compounds.
MCRs are considered as a striking and powerful pro-
tocol for the synthesis of a wide range of organic com-
pounds in comparison with multi‐step reactions due to
the simultaneous generation of several new bonds in a
one‐pot fashion. The other apparent advantages are low
number of reaction and purification steps, selectivity,
being convergent, showing high atom economy, simplic-
ity, and synthetic efficiency.[9] As a matter of fact, devel-
opment of MCRs have resulted in novel and effective
synthetic pathways to provide a plethora of small organic
molecules in the field of modern organic, bio‐organic,
and medicinal chemistry.[10]
We are interested in heterocyclic chemistry[35] and espe-
cially in the synthesis of heterocyclic systems via MCR[36]
being performed under heterogeneous catalysis in water.[37]
We have recently reported the synthesis of pyran derivatives
by using heteropolyacids as support in water[38] and
electrosynthesis.[39] From the last decade till date our
research group has manipulated different heteropolyacids
FIGURE 1 Distribution of the synthesized compounds for the
three types of HPAs; H5BW12O40 (BW), H3PW12O40 (PW) and
H4SiW12O40 (SiW).

HERAVI ET AL.
3 of 10
as efficient catalysts in the art of organic synthesis which
have been cited in two comprehensive reviews.[40]
refluxed in a mixture of EtOH/H2O (1:1) (5 ml) for the
indicated reaction time. The progress of the reaction was
monitored by TLC (7:3 n‐hexance/ethylacetate). Upon
completion of the reaction (indicated by TLC), the mixture
was filtered off under vacuum. The filtrate was cooled to
room temperature and the precipitated solid as the reaction
product was isolated by filtration. The crude products were
purified by recrystallization from a mixture of EtOH/H2O
to give the corresponding desired products. These products
were identified by comparison of their melting points along
A literature survey showed that the one‐pot three‐
component synthesis of 4H‐pyrans can be catalyzed in
the presence of acidic as well as basic catalysts. Thus,
based on the above facts and as a part of our research
program to develop selective, efficient and green methods
in organic synthesis, herein we wish to reveal for the first
time the application of a newly reported heteropolyacid
(BWA) acting as an efficient, green, and homogeneous
but reusable catalyst for the diversity‐oriented synthesis
1
with their FTIR spectra and in two cases (4b and 4d) H‐
of 4H‐pyrans via
a
one‐pot three‐component
NMR.
cyclocondensation reaction between aldehydes 1,
malononitrile 2 and carbonyl compounds 3 possessing a
reactive α‐methylene group in the presence of BWA in
refluxing EtOH/H2O (Scheme 1).
Selected spectral data
1. 2‐Amino‐4‐(4‐chlorophnyl)‐7,7‐dimethyl‐5‐oxo‐5,6,7,
8‐tetrahydro‐4H‐chromene‐3‐carbonitrile (4a):[21]
FT‐IR (KBr): υmax = 3367, 3191, 2969, 2194, 1687,
2 | EXPERIMENTAL
2.1 | Materials
1658, 1606, 1510, 1490 cm−1
;
1H‐NMR (CDCl3,
400 MHz): δ = 1.1 (3H, s, CH3), 1.1 (3H, s, CH3), 2.2
(2H, s, CH2), 2.5 (2H, s, CH2), 4.5 (1H, s, CH), 6.3 (2H,
s, NH2), 7.4 (2H, d, J = 8.0, ArH), 8.0 (2H, d, J = 8.0,
ArH) ppm; 13C‐NMR (DMSO‐d6): δ = 27.5 (Me), 29.0
(Me), 32.5 (C‐7), 35.8 (C‐4), 40.4 (C‐8), 50.6 (C‐6), 58.5
(C‐3), 113.0 (C‐4a), 120.2 (CN), 129.0, 130.0, 131.8,
144.4, (C‐Ar), 159.2 (C‐2), 163.2 (C‐8a), 196.3 (C‐5) ppm.
All chemicals employed for the investigating of the cata-
lytic activity of the BWA as catalyst were purchased from
Merck Company and used as received. Heteropolyacid,
H5BW12O40 (BWA) was prepared in accordance with pro-
cedure reported in 2015.[41] Melting points were mea-
sured by an electrothermal 9200 apparatus. IR spectra
were recorded on the FT‐IR Tensor 27 Spectrophotome-
ter. Nuclear magnetic resonance (NMR) spectra were
recorded on a Bruker Avance 400 MHz Spectrometer in
CDCl3 as a solvent. All products were known and identi-
fied by comparison of their physical (melting points) and
spectral (FTIR spectra) with those of authentic samples
which were found being identical. For more certainty
1H‐NMR of spectra of two products (4b and 4d) were
also recorded which are given in supplementary section
along with their FTIR spectra. Synthesis of 4H‐pyrans:
General Procedure.
2. 2‐Amino‐4‐(3‐nitrophenyl)‐7,7‐dimethyl‐5‐oxo‐5,6,7,
8‐tetrahydro‐4H‐chromene‐3‐carbonitrile (4b):[21]
FT‐IR (KBr): υmax
= 3400, 3300, 3195, 2200,
695,1600 cm‐1, 1H‐NMR (CDCl3, 400 MHz): δH = 1.01 (s,
3H, Me), 1.1 (s, 3H, Me), 2.3 (s, 2H, 8‐H), 2.5 (m, 2H, 6‐H),
4.2 (s, 1H, 4‐H), 5.0 (s, 2H, NH2), 7.4–8.0 (m, 4H, ArH) ppm.
3. 2‐Amino‐4‐(4‐metoxyphenyl)‐7,7‐dimethyl‐5‐oxo‐
5,6,7,8‐tetrahydro‐4H‐chromene‐3‐carbonitrile
(4c):[21]
A mixture of an appropriate aldehyde (1 mmol),
malononitrile (1 mmol) and dimedone, 4‐hydroxycoumarin
or 3‐methyl‐4H‐pyrazole‐5(4H)‐one (1 mmol) in the pres-
ence of catalytic amount of (H5BW12O40) (10 mol %) was
FT‐IR (KBr) υmax = 3377, 3186, 2963, 2194, 1680,
1658, 1606, 1510, 1463 cm−1
;
1H‐NMR (CDCl3,
400 MHz); δ = 1.0 (3H, s, CH3), 1.2 (3H, s, CH3), 2.2
SCHEME 1 Synthesis of 4H‐pyran
derivatives 4 via one‐pot and
multicomponent reaction

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HERAVI ET AL.
(2H, s, CH2), 2.4 (2H, s, CH2), 3.8 (3H, s, OCH3), 4.4 (1H,
s, CH), 4.5 (2H, br s, NH2), 6.8 (2H, d, J = 6.8, ArH), 7.1
(2H, d, J = 6.8, ArH) ppm; 13C‐NMR (DMSO‐d6): δ = 27.5
(Me), 29.1 (Me), 32.5 (C‐7), 35.4 (C‐4), 40.4 (C‐8), 50.7 (C‐
6), 55.7 (OMe), 59.3 (C‐3), 113.7 (C‐4a), 120.4 (CN), 114.4,
129.0, 137.5, 158.6 (C‐Ar), 159.1 (C‐2), 162.8 (C‐8a), 196.3
(C‐5) ppm.
8. 2‐Amino‐5‐oxo‐4‐phenyl‐4,5‐dihydropyrano[3,2‐c]‐
chromene‐3‐carbonitrile (4h):[42]
FT‐IR (KBr) υmax = 3350, 3320, 2921, 2852, 2195,
1700, 1669, 1603, 1373, 1044, 759 cm−1
;
1H‐NMR
(300 MHz, DMSO‐d6) δ = 7.9 (1H, d, J = 7.8 Hz), 7.7
(1H, t, J = 6.9 Hz), 7.4–7.5 (3H, m), 7.2–7.3 (5H, m),
4.5 (1H, s) ppm; 13C‐NMR (75 MHz, DMSO‐d6)
δ = 159.5, 157.9, 153.4, 152.1, 143.3, 132.9, 128.5,
127.6, 127.1, 124.6, 122.4, 119.2, 116.5, 112.9, 104.0,
57.9, 36.9 ppm.
4. 2‐Amino‐4‐(phenyl)‐7,7‐dimethyl‐5‐oxo‐5,6,7,8‐
tetrahydro‐4H‐chromene‐3‐carbonitrile (4d):[21]
FT‐IR (KBr): υmax = 3390, 3290, 2935, 2200, 1685,
1
1600 cm−1; H‐NMR (CDCl3, 400 MHz): δ = 1.0 (s, 3H,
9. 2‐Amino‐4‐(3‐nitrophenyl)‐5‐oxo‐4,5‐dihydropyrano‐
[3,2‐c]chromene‐3‐carbonitrile (4i):[42]
Me), 1.0 (s, 3H, Me), 2.1 (d, 1H, J = 16.0 Hz, 8‐H), 2.2
(d, 1H, J = 16.0 Hz, 8‐H), 2.4–2.5 (m, 2H, 6‐H), 4.3 (s,
1H, 4‐H), 6.1 (s, 2H, NH2), 7.1–7.3 (m, 5H, ArH) ppm.
FT‐IR (KBr) υmax = 3398, 3323, 3190, 3087, 2194,
1
1712, 1674, 1603, 1532, 1379, 1212, 1063 cm−1; H‐NMR
5. 2‐Amino‐4‐(4‐methylphenyl)‐7,7‐dimethyl‐5‐oxo‐
5,6,7,8‐tetrahydro‐4H‐chromene‐3‐carbonitrile (4e):[21]
(400 MHz, DMSO‐d6) δ = 4.7 (1H, s, CH), 7.2–7.9 (10H,
m, Ar–H and NH2) ppm; 13C‐NMR (100 MHz, CDCl3):
δ = 38.0 (C–H), 59.8 (=C–CN), 102.7, 112.8 (C=C),
116.4 (C–H Ar), 119.8 (C ≡ N), 122.1, 124.3, 123.5,
125.5, 130.0, 133.0, 134.6 (C–H Ar), 145.4 (C=C), 148.7
(=C–NO2), 152.2 (=C–NH2), 153.7, 159.1 (=C–O), 159.5
(O=C–O) ppm;
FT‐IR (KBr) υmax = 3425, 3330, 3266, 3221, 2191,
1675, 1638, 1602, 1367 cm−1
;
1H‐NMR (DMSO‐d6,
500 MHz): δ =1.8–1.9 (1H, m), 1.9–2.0 (1H, m), 2.2–2.3
(5H, m), 2.6 (2H, m), 4.1 (1H, s), 6.9 (2H, s), 7.0 (2H, d,
J = 8.0 Hz), 7.0 (2H, d, J = 8.0 Hz,) ppm; 13C‐NMR
(DMSOd6, 125 MHz): δ = 20.6, 21.4, 27.3, 35.9, 37.2,
59.2, 114.8, 120.6, 127.9, 129.7, 136.4, 142.7, 159.3, 165.1,
196.6 ppm.
10. 6‐Amino‐3‐methyl‐4‐phenyl‐1,4‐dihydropyrano[2,3‐
c]pyrazole‐5‐carbonitrile (4k):[43]
1H NMR (400 MHz; CDCl3; Me4Si): δ = H 1.8 (3H, s,
CH3), 4.6 (1H, s), 6.9 (2H, br, s, NH2), 7.1 (2H, d,
J = 7.3 Hz), 7.2 (1H, m), 7.3–7.3 (2H, m), 12.1 (1H, s,
NH) ppm; 13C‐NMR (100 MHz; CDCl3): δ = 9.7, 36.2,
57.2, 97.6, 120.8, 126.7, 127.5, 128.4, 135.6, 144.4, 154.8,
160.9 ppm.
6. 2‐Amino‐4‐(4‐chlorophenyl)‐5‐oxo‐4,5‐
dihydropyrano‐[3,2‐c]chromene‐3‐carbonitrile (4f):[42]
FT‐IR (KBr) υmax = 3404, 2924, 2255, 2184, 2128,
1704, 1668, 1378, 1026, 1001, 763 cm−1;1H NMR
(300 MHz, DMSO‐d6); δ = 7.9 (1H, d, J = 7.5 Hz), 7.7
(1H, t, J = 7.5 Hz), 7.4–7.5 (3H, m), 7.3–7.4 (4H, d,
J = 8.4 Hz, 19.5 Hz), 4.5 (1H, s) ppm; 13C‐NMR
(75 MHz, DMSO‐d6) δ = 160.0, 158.4, 154.0, 152.6,
142.8, 133.5, 132.2, 130.1, 128.9, 125.1, 123.0, 119.5,
117.0, 113.4, 103.9, 58.0, 36.8 ppm.
11. 6‐Amino‐4‐(4‐chlorophenyl)‐3‐methyl‐
2,4dihydropyrano[2.3‐c]pyrazol‐5‐carbonitrile (4l):[43]
FT‐IR (KBr) υmax = 3483, 3357, 3221, 2210, 1634,
1
1600 cm−1; H‐NMR (400 MHz, DMSO‐d6) δ = 1.9 (3H,
s, CH3), 4.6 (1H, s, CH), 7.0 (2H, s, NH2), 7.3 (2H, d,
J = 8.4 Hz, ArH), 8.1 (2H, d, J = 8.4 Hz, ArH), 11.9
(1H, s, NH) ppm.
7. 2‐Amino‐4‐(4‐methoxyphenyl)‐5‐oxo‐4,5‐
dihydropyrano‐[3,2‐c]chromene‐3‐carbonitrile (4g):[42]
FT‐IR (KBr) υmax = 3364, 3313, 3177, 2920, 2850,
12. 6‐Amino‐4‐(4‐methylpheny)‐3‐methyl‐
2,4dihydropyrano[2.3‐c]pyrazol‐5‐carbonitrile
(4n):[43]
2189, 1710, 1668, 1371, 1051, 766 cm−1 1H NMR
;
(300 MHz, DMSO‐d6) δ = 7.9 (1H, d, J = 7.8 Hz), 7.7
(1H, t, J = 7.5 Hz), 7.4–7.5 (3H, m), 7.2–7.3 (1H, t,
J = 8.4 Hz), 6.8 (1H, s), 6.8 (2H, s), 4.4 (1H, s), 3.7 (3H,
s) ppm; 13C‐NMR (75 MHz, DMSO‐d6) δ = 159.5, 159.2,
157.9, 153.4, 152.1, 144.8, 132.9, 129.6, 124.6, 122.4,
119.7,119.1, 116.5, 113.8, 112.9, 111.9, 103.8, 57.8, 54.9,
36.8 ppm.
FT‐IR (KBr) υmax = 3406, 3315, 3188, 2191, 1646,
1
1600 cm−1; H‐NMR (400 MHz, DMSO‐d6) δ = 1.8 (3H,
s, CH3), 3.9 (3H, s, CH3), 4.6 (1H, s, CH), 6.9 (2H, s,
NH2), 7.4 (2H, d, J = 8.4 Hz, ArH), 8.1 (2H, d,
J = 8.4 Hz, ArH), 11.9 (1H, s, NH) ppm.

HERAVI ET AL.
5 of 10
13. 6‐Amino‐4‐(4‐metoxyphenyl)‐3‐methyl‐
friendly conditions and our special interest using HPAs
as efficient and green catalysts,[49] we synthesized a
newly reported HPA, H5BW12O40 (BWA). This HPA was
also developed as an electrolyte for solid super capaci-
tors[8] but its catalytic activity in organic transformations
has not been investigated, thus for the first time we exam-
ined it as an efficient catalyst in a typical organic transfor-
mation. Its structure was well characterized by using
FTIR and XRD, which were compared to those of the
known silicotungstic acid H4SiW12O40, (SiWA) HPA.
Boron trifluoride is most typically used as Lewis acid
catalyst in several organic reactions.[50] Examples
include: as initiator in polymerisation reactions of unsat-
urated compounds, such as polyethers[51] and some other
polymerization, isomerization, acylation,[52] alkylation,
esterification, dehydration, condensation, Mukaiyama
2,4dihydropyrano[2.3‐c]pyrazol‐5‐carbonitrile (4o):[43]
FT‐IR (KBr) υmax = 3483, 3249, 3122, 2190, 1643,
1
1600 cm−1; H‐NMR (400 MHz, DMSO‐d6) δ = 1.9 (3H,
s, CH3), 3.8 (3H, s, CH3), 4.6 (1H, s, CH), 6.9 (2H, s,
NH2), 7.4 (2H, d, J = 8.4 Hz, ArH), 8.1 (2H, d,
J = 8.4 Hz, ArH), 11.9 (1H, s, NH) ppm.
2.2 | Results and discussion
In general, the difference between homogeneous and
heterogeneous catalysis needs further refinement.
Homogeneous catalysis is a reaction or process, where
the catalyst is the same phase as the reactants. Thus in
homogeneous catalysis two or three‐phases can be pres-
ent (for example two‐phase catalysis or liquid–gas reac-
tions) but the reaction should take place in the phase
where the catalyst is present (the reactants need to
dissolve into the catalysts phase). In case of heteroge-
neous catalysts, which typically a solid, the reactants are
in another phase, usually liquids, liquids‐gases or gases.
Thus, one can conclude that homogeneous catalysis
should be more efficient whereas the separation of
heterogeneous catalyst is generally much easier (simple
filtration, or just passing the reactants through a solid
bed) and more importantly the heterogeneous can be
reused after separation.[44]
We have already found out that HPAs have both
advantages in addition of being green and acting
efficiently in water as the greenest solvent and since
organic compounds are rarely soluble in water due to
their inherent lipophilicity.[40a, 45] In the last decade, we
established HPAs as efficient heterogeneous[46] and
homogeneous catalysts,[47] which were both were easily
separated from the reaction mixture. In both cases, they
could be effectively reused for several times without loss
of their catalytic activities.
We have also observed and reported that Keggin‐type
heteropolyacids show high catalytic activities for many
organic transformations. It has been shown that the cata-
lytic activities of the heteropolyacids were much higher
than those of traditional acid catalysts such as sulfuric
acid and p‐toluensulfonic acid.[48] On the basis of
comparative measurements of electrical conductivity,
acidity, and softness of anion for the solutions of acid cat-
alysts, the effectiveness acid catalysis by heteropolyacid
was proposed to be due to the specific properties of the
heteropoly anion, which can be characterized by very
weak basicity and great softness, along with the large size
of the polyhedral structure.
aldol addition and etc.[53] H5BW12O40 (BWA),
a
heteropolyacid having B3+ as the central heteroatom
attracted our attention and we thought it is worthwhile
to examine its catalytic activity as a stronger Lewis acid
than boron tetrafluoride etherate in the synthesis of a het-
erocyclic system via MCR.
Initially, the necessity of the presence of the catalyst
was studied. For this purpose, the reaction of benzalde-
hyde, malononitrile and dimedone was selected as the
model reaction and performed it in water as solvent but
in the absence of the any catalyst. In the absence of
catalyst the reaction proceeded sluggishly and only trace
amount of the desired product was obtained. Then, we
prepared H5BW12O40 (BWA) according to the procedure
already reported.[41] The aforementioned reaction was
conducted in the presence of catalytic amount of
H5BW12O40 (BWA). The progress of reaction was moni-
tored by TLC (7:3 n‐hexance/ethylacetate). This monitor-
ing showed the smooth and clean conversion of starting
materials along with the generation of the expected prod-
uct. To find the optimal reaction conditions, the influence
of solvent, quantities of catalyst loading and temperature
were examined in a model reaction involving benzalde-
hyde, dimedone and malononitrile. The results are shown
in Table 1. The effects of various solvents, polar and non‐
polar were examined in this reaction. Initially, to find the
best solvent, the model reaction was conducted in sol-
vent‐free conditions. Then, water as the greenest solvent
was used which gave the desired compound 4a in 75%
yield (Table 1, entry 1). In addition, we examined other
solvents such as EtOH, DMF, CH3CN and CH2Cl2. As
illustrated in Table 1, when the above‐mentioned reac-
tion was performed in DMF, gave the expected product
4a in only 50% yield (Table 1, entry 3). In CH2Cl2 product
4a was obtained in 60% yield (Table 1, entry 2). EtOH and
CH3CN provided the corresponding products in, 78 and
85% yield respectively (Table 1, entries 4 and 5).
In continuation of our interest in the catalytic synthe-
sis of heterocyclic compounds via MCR under eco‐

6 of 10
HERAVI ET AL.
TABLE 1 Optimization of reaction conditions for the synthesis of
4H‐pyrans
4a was generated in 98% yield after 60 minutes (Table 1,
entry 9).
With these results in hand, we then investigated the
substrate scopes and limitations of the synthesis of 4H‐
pyrans in the presence of 10 mol% BWA as catalyst under
reflux condition in EtOH/H2O and the results are listed
in Table 2. The generality of the current method was
investigated in the reaction of differently substituted
aldehydes, containing either electron donating or
electron‐withdrawing functional groups in the ortho,
meta, and para positions with malononitrile and either
dimedone or 4‐hydroxycoumarin or 3‐methyl‐4H‐
pyrazole‐5(4H)‐one under already secured optimal reac-
tion condition (Scheme 1). The corresponding 4H‐pyran
derivatives were obtained in good to excellent yields in
relatively short times without formation of any by‐prod-
ucts. The results are summarized in Table 2. As can be
realized, in all cases the desired products successfully
produced with in satisfactory yields.
Catalyst
Time amount Yield
Temperature (min) (mol%) (%)
Entry Solvent
1
H2O
Reflux
Reflux
Reflux
Reflux
Reflux
120
180
180
90
10
10
10
10
10
10
‐
75
60
2
CH2Cl2
DMF
3
50
4
EtOH
CH3CN
85
5
90
78
6
EtOH/H2O Room
EtOH/H2O Reflux
EtOH/H2O Reflux
EtOH/H2O Reflux
EtOH/H2O Reflux
420
420
60
50
7
trace
85
8
5
9
60
10
15
98
10
60
98
Extraordinarily, the best results (98% yields) was reached
when the model reaction was conducted in EtOH/H2O
(1:1) at reflux condition (Table 1, entry 9). Since, polar
protic solvents such as EtOH/H2O, raised the yields sub-
stantially. This might be due to the more solubility of
starting materials in polar solvents. Thus, EtOH/H2O
(1:1) was selected as the solvent of choice.
In the following, in order to find the influence of tem-
perature, the model reaction was conducted in the pres-
ence of H5BW12O40 (BWA) in EtOH/H2O at ambient
temperature that gave only 50% yield (Table 1, entry 6).
This model reaction under reflux condition in EtOH/
H2O led to the desired products in highest yield (98%
yield) (Table 1, entry 9).
As illustrated, aldehydes bearing electron‐donating
groups (such as 4‐MeO‐benzaldehyde and 4‐Me‐benzal-
dehyde) as well as electron‐withdrawing groups (such as
3‐NO2‐benzaldehyde and 4‐Cl‐benzaldehyde) were used
as substrate. The reaction of benzaldehyde, malononitrile
and dimedone 3a provided the desired product 4d after
50 min in 98% yield (Table 2, entry 4). Aldehydes contain-
ing electron‐donating groups containing 4‐OMe, 4‐Me
provided the desired products 4c and 4e in 90 and 88%
yield respectively (Table 2, entries 3 and 5). Also, alde-
hydes containing electron‐withdrawing groups including
4‐Cl and 3‐NO2 gave the corresponding products 4a and
4b in 92 and 85% yields respectively (Table 2, entries 1
and 2).
Finally, to find the effect of the catalyst amount, the
model reaction was conducted without any catalyst
which failed (Table 1, entry 7), while in the presence of
5 mol%, BWA the desired product was isolated in 85%
which indicated the important role of our catalyst in the
reaction progress (Table 1, entry 8). As expected, the yield
was increased from 85% to 98% with raising BWA amount
from 5 mol% to 10 mol% (Table 1, entry 9). The improve-
ment of the yield by increasing the BWA quantity can be
attributed to the increase in the number of active sites as
well as the amended and enhanced the contact and
collision opportunity between the BWA surface with the
molecules of the starting materials. Worthy to mention
that further increase in the BWA amount from 10 mol%
to 15 mol% resulted in no change in yield % (Table 1,
entry 10). Thus, 10 mol% of catalyst was chosen as the
optimized catalyst loading (Table 1, entry 9). The best
result was obtained when the reaction was conducted in
the presence of 10 mol% catalyst in EtOH/H2O
under reflux condition, which corresponding 4H‐pyran
In the following, as we mentioned above, for library val-
idation, we examined 4‐hydroxycoumarin and 3‐methyl‐
4H‐pyrazole‐5(4H)‐one instead of dimedone, which gave
the corresponding products in good to excellent yields.
2.3 | Reaction Mechanism
In
a
proposed mechanism (Scheme 2), firstly,
malononitrile reacts with carbonyl group of aldehyde,
which already is activated by the BWA and affords
intermediate 1 after removing one molecule of H2O.
Dimedone converts to enole form after tautomerisation
and attacks to cyanoolefin compound 1 as Michael accep-
tor to produce 2. Finally, cyclocondensation of 2 gives 3
which is converted to the desired product.
To display the merits of this catalyst, its catalytic
activity for the development of the model compound
(benzaldehyde, malononitrile and dimedone) was com-
pared with those surveyed previously (Table 3). As shown
in Table 3, the catalytic activity of BWA was compared

HERAVI ET AL.
7 of 10
TABLE 2 Synthesis of 4H‐pyrans in the presence of H5BW12O40 in EtOH/H2O under reflux condition
Time
(min)
mp (°C)
Found
mp (°C)
Lit
Entry
Product 4
Carbonyl compound 3
R1
Yield (%)
1
4a
4b
4c
4d
4e
4f
3a
3a
3a
3a
3a
3b
3b
3b
3b
3b
3c
3c
3c
3c
3c
4‐Cl
92
85
90
98
88
98
85
98
90
85
94
90
92
77
90
75
300
255
60
206
212
203–205[58]
209–211[58]
201–202[43]
224–225[59]
215–216[21]
233–234[60]
220–222[61]
258–260[59]
256–257[61]
266–268[42]
244–246[62]
234–236[62]
223–224[62]
215–217[63]
212–213[64]
2
3‐NO2
4‐ OCH3
H
3
198
4
221–223
212–213
230–232
222
5
4‐CH3
4‐Cl
90
6
270
270
210
195
225
120
90
7
4g
4g
4i
4‐OCH3
H
8
257–258
253–255
264–268
244–246
232
9
3‐NO3
4‐OH
H
10
11
12
13
14
15
4j
4k
4l
4‐Cl
4m
4n
4o
4‐OH
4‐CH3
4‐ OCH3
190
90
224
213
120
212
SCHEME 2 Suggested mechanism for
the synthesis of 4H‐pyran derivatives

8 of 10
HERAVI ET AL.
TABLE 3 The comparison of the catalytic activity of H5BW12O40 with formerly reported catalysts
Catalyst
Yield
Entry
Catalyst
Time
Amount
Temperature
Solvent
(%)
Ref.
[54]
1
POPINO
15 min
5 mmol%
reflux
H2O
95
(Potassium phthalimide‐N‐oxyl)
[55]
[19]
[23]
2
3
4
nano ZnO
180 min
120 min
35 min
10 mmol%
5 mmol%
6 mmol%
r.t.
EtOH/H2O
EtOH/H2O
EtOH/H2O
86
82
96
(S)‐proline
reflux
reflux
Silica bonded n‐propyl‐4‐aza‐1‐
azoniabicyclo[2.2.2] octane
chloride (SB‐DABCO)
[65]
5
nano‐TiO2/
20 min
25 mg
ultrasound
EtOH
93–95
H14[NaP5W30O110
]
[66]
[56]
6
7
LiBr
15 min
20 min
10 mmol%
15 mg
reflux
reflux
H2O
H2O
95
94
Fe3O4@SiO2‐Imid‐PMAn
PMAn: nano H3PMo12O40
[57]
[21]
8
9
Na2SeO4
60 min
10 mg
reflux
reflux
EtOH/H2O
H2O
97
91
Hexadecyltrimethyl ammonium
bromide (HTMAB)
180 min
10 mmol%
[22]
[25]
10
11
RE (PFO)3
300 min
25 min
5 mmol%
0.2 mol%
90 °C
50 °C
EtOH
H2O
90
95
Magnetic Fe3O4
/phenylsulfonic acid
[26]
[27]
12
13
Nano‐SiO2
8 min
5 min
20 mol%
0.02 g
70 °C
reflux
H2O
94
92
HPA‐den drimer functionalized
ma gnetic nanop article
(Fe3O4@ D‐NH2‐HPA)
EtOH
[28]
[29]
14
15
Mixed‐ligand Cu (II) Schiff base
complex (Cu (L)(Py))
15 min
1 min
20 mg
10 mg
50 °C
EtOH
Neat
95
92
Amine‐functionalized
Room
hyper‐crosslinked polyphenanthrene
temperature
[31]
[32]
16
17
Polypyrrole/Fe3O4/CNT
15 min
60 min
0.032 g
90 °C
Solvent‐free
95
92
Polystyrene‐supported
10 mol%
Room
H2O
DABCO ionic liquid
temperature
[33]
[34]
18
19
12‐molybdophos phoric acid
encapsulated in the nanocavities
of modified dealuminated zeolite Y
15 min
15 min
140 mg
0.03 g
80 °C
EtOH
89
88
Magnetite‐dihydrogen phosphate
60 °C
Solvent‐free
with diverse catalysts such as POPINO (Potassium
phthalimide‐N‐oxyl),[54] nano ZnO,[55] (S)‐proline,[19]
Fe3O4@SiO2‐Imid‐PMAn,[56] (PMAn: nano H3PMo12O40)
Na2SeO4,[57] which have been previously employed as
catalysts in the aforementioned reaction. The findings
demonstrated that comparing to other catalysts; our
planned catalyst can mediate the reaction in an appropri-
ate amount. Furthermore, it supplies the corresponding
products in short reaction time. From the green chemis-
try point of view, the reusability of the catalyst and using
EtOH/H2O as the reaction media render this catalyst
green and eco‐friendly. Notably, the purpose of this work,
which is presenting a catalyst with potential usage for
improving organic reactions and synthesis of 4H‐pyrans
is just particular as a model organic transformation.
2.4 | Catalyst reusability
Finally, as shown in Figure 2, we investigated the reus-
ability of the catalyst. The catalyst was soluble in EtOH/
H2O and could be removed easily by evaporation of the
solvent. After evaporating of solvent, the catalyst was
washed with diethyl ether, dried at 130 °C for 1 h, and
re‐used in another reaction. The recycled catalyst was
used for three consecutive reactions without observation
of appreciable loss in its catalytic activities.

HERAVI ET AL.
9 of 10
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In this work, we introduce the first example of catalytic
activity of the heteropoly acid, H5BW12O40 as an efficient,
green, reusable and homogeneous catalyst for a one‐pot
three‐component synthesis of 4H‐pyran derivatives in
EtOH/H2O under reflux condition which are biologically
and pharmacologically active compounds. This method
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The authors appreciate partial financial supports from
Alzahra University. MMH is also thankful to Iran National
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MM gratefully acknowledges the financial support by the
Ferdowsi University of Mashhad, Mashhad, Iran (Grant
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ORCID
[25] D. Elhamifar, Z. Ramazani, M. Norouzi, R. Mirbagheri,
Majid M. Heravi http://orcid.org/0000-0003-2978-1157
Masoud Mirzaei http://orcid.org/0000-0002-7256-4601
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SUPPORTING INFORMATION
Additional supporting information may be found online
in the Supporting Information section at the end of the
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Beheshtiha SYS, Zadsirjan V, Mashayekh Ameli F,
Bazargan M. H5BW12O40 as a green and efficient
homogeneous but recyclable catalyst in the
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