BiVO4-NPs: an efficient nano-catalyst for the synthesis of biscoumarins, bis(indolyl)methanes and 3,4-dihydropyrimidin-2(1H)-ones (thiones) derivatives

Article abstract of DOI:10.1007/s13738-016-0959-y

BiVO₄-NPs can be used as an efficient and reusable nano-catalyst for the promotion of the synthesis of biscoumarins, bis(indolyl)methanes and 3,4-dihydropyrimidin-2(1H)-ones (thiones) derivatives. The structures of the products were characteriz

Full text of DOI:10.1007/s13738-016-0959-y

J IRAN CHEM SOC
DOI 10.1007/s13738-016-0959-y
ORIGINAL PAPER
BiVO4‑NPs: an efficient nano‑catalyst for the
synthesis of biscoumarins, bis(indolyl)methanes
and 3,4‑dihydropyrimidin‑2(1H)‑ones (thiones) derivatives
Farhad Shirini1 · Monireh Pourghasemi Lati1
Received: 23 April 2016 / Accepted: 8 August 2016
© Iranian Chemical Society 2016
Abstract BiVO4-NPs can be used as an efficient and reus-
able nano-catalyst for the promotion of the synthesis of bis-
coumarins, bis(indolyl)methanes and 3,4-dihydropyrimi-
din-2(1H)-ones (thiones) derivatives. The structures of the
products were characterized by IR, 1H NMR and 13C NMR
spectroscopy and comparison with the authentic samples.
Easy work-up procedure, excellent yields, short reaction
times and reusability of the catalyst are some advantages of
this work. In addition, in this article and for the first time,
the preparation of 3,4-dihydropyrimidin-2(1H)-ones and
-thiones from the protected derivatives of aldehydes includ-
ing oximes, semicarbazones and 1,1-diacetates is reported.
activities such as anti-HIV [5], anti-viral [6], antipyretic
[7], anti-thrombotic [8], antimicrobial [8], anticancer [9],
antioxidant [5, 10, 11], urease inhibitory [12], cytotoxicity
and enzyme inhibitory [13] activities.
The most direct procedure for the preparation of bis-
coumarins includes the condensation of an aldehyde with
4-hydroxycoumarin in the presence of hazardous cata-
lysts, such as glacial acetic acid and acetic anhydride [14],
SBPPSP [15], piperidine [12], ruthenium(III) chloride
hydrate [16], manganous chloride [17], phosphotungstic
acid [18], HBF4 [19], surfactants like TBAB [19] or DDS
[20], SBPDSA [21], POCl3 in dry DMF [22] and B(HSO4)3
[23]. Therefore, introduction of efficient and economical
catalysts that solve these drawbacks is desirable.
Bis(indolyl)methanes (BIMs) feature widely in bioac-
tive metabolites of terrestrial and marine origin [24]. These
types of compounds are also known to promote estro-
gen metabolism in both women and men and is expected
to have an application in prevention of breast cancer [25].
Therefore, significant efforts have been directed toward the
synthesis of these molecules. To improve the rate of this
type of reactions, a variety of catalysts have been reported,
of which HCl [26], NBS [27], trichloro-1,3,5-triazine [28],
I2 [29, 30], KHSO4·SiO2 [31], tetrabutylammonium tri-
bromide (TBATB) [32], benzyltriphenylphosphonium tri-
bromide (BTPTB) [33], NaHSO4·SiO2 [34], HClO4·SiO2
[35], ZrOCl2.8H2O/SiO2 [36], SiO2 [37], P2O5/SiO2 [38],
AlPW12O40 [39], H3PW12O40 [40], H6P2W18O62 [41],
ZrCl4 [42], silica sulfuric acid [43], polyindole salt [44],
montmorillonite K-10 [45], dodecyl sulfates [46], TPA
ZrO4 [47], sulfamic acid [48], aminosulfonic acid [49],
RuCl3·nH2O [50], silica-bonded S-sulfonic acid (SBSSA)
[51], La(PFO)3 [52], M(HSO4)x [53], V(HSO4)3 [54],
HPA/TPI-SBA-15 [55], squaric acid (SQ) [56], [Et3NH]
[H2PO4] [57], 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP)
Keywords BiVO4-NPs · Multi-components ·
Biscoumarins · Bis(indolyl)methanes · Biginelli reaction ·
Reusable catalyst
Introduction
Multi-component reactions (MCRs) play an important
role in combinatorial chemistry because of its ability to
synthesize small drug-like molecules with several degrees
of structural diversity. MCRs have performed quantita-
tive revolutions in molecular architecting, access to multi-
functional molecules and combinatorial chemistry in recent
years [1–4].
Biscoumarins are a large group of heterocycles with
diverse and interesting biological and pharmaceutical
* Farhad Shirini
shirini@guilan.ac.ir
1
Department of Chemistry, College of Science, University
of Guilan, Rasht zip code 41335, Islamic Republic of Iran
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J IRAN CHEM SOC
[58], [BTBAC]Cl-FeCl3 [59] and [bnmim][HSO4] [60]
are examples. However, disadvantages such as long reac-
tion times [53, 56], lower product yields, tedious work-up
procedure, the use of expensive or toxic reagents [26, 29,
30, 50], use of a larger amounts of the catalyst [38, 57] and
use of an additional microwave or ultrasound irradiation
are reported in most of these procedures. Therefore, intro-
duction of new methods and catalysts for the preparation of
BIMs is still in demand.
Dihydropyrimidinones as products of the Biginelli reac-
tion are important classes of compounds and exhibit signif-
icant biological and pharmaceutical properties such as anti-
viral [61, 62], anti-bacterial [62], antihypertensive [63] and
calcium channel blockers [64, 65], as well as anti-tumor
activities [61]. This reaction is based on a one-pot conden-
sation reaction of β-dicarbonyl compounds with aldehydes
and urea or thiourea in the presence of an acid catalyst [66].
To improve the Biginelli’ results, several methodologies
were reported in the literature using different reagents, of
which zeolites [67, 68], HClO4–SiO2 [69], H4SiW12O40
[70], Cu(OTf)2 [71], Zn(OTf)2 [72], SiO2–MCl4_n (M=Sn,
Ti) [73], M(HSO4)n [74], LaCl3 [75, 76] are examples.
Most of the reported methods suffer from drawbacks such
as harsh reaction conditions, use of harmful organic sol-
vents, long reaction times, tedious work-up procedure,
expensive and moisture-sensitive reagents, strongly acidic
conditions, unsatisfactory yields, non-recoverability of the
catalyst and environmental pollution. Thus, it is important
to find more efficient catalysts and methods for the synthe-
sis of these types of compounds.
General procedure for the synthesis of BiVO4
Bi(NO3)3·5H2O (p.a., Kemika), NH4VO3 (p.a., Merck),
tetramethylammonium hydroxide, TMAH, (CH3)4NOH,
25 % (w/w) aqueous solution, electronic grade, 99.999 %
(metal basis) (Alfa Aeserw) and doubly distilled water
were used. The sample was synthesized under the experi-
mental conditions summarized in Table 1.
Sample BiV-2 was synthesized using a hydrother-
mal route. Twenty milliliters of 4 M HNO3 was added
to 0.03 mol of Bi(NO3)3·5H2O and then stirred for 2 h
at RT in a closed flask. A clear (homogeneous) solution
was obtained. Separately, 20 mL of 25 % (w/w) aqueous
solution of TMAH was added to 0.03 mol of NH4VO3
and stirred for 2 h in a closed plastic bottle. Ammonium
vanadate was also fully dissolved in an aqueous solu-
tion of TMAH. These two clear solutions were mixed and
then stirred at RT for additional 30 min. The solution thus
obtained was quantitatively transferred to a 50-mL Teflon-
lined stainless autoclave, sealed and allowed to heat at
170 °C for 130 h. The precipitate formed was isolated by
centrifugation, washed several times with doubly distilled
water and dried in a laboratory oven for 24 h at 60 °C [77].
General procedure for the synthesis
of bis‑(4‑hydroxycoumarin‑3‑yl)methanes
A mixture of aldehyde (1 mmol), 4-hydroxycoumarin
(2 mmol) and BiVO4-NPs (30 mg) in H2O (3 mL) was
stirred at 80 °C for the appropriate time. After completion
of the reaction (monitored by TLC), the mixture was cooled
to room temperature and the solvent was evaporated. Then
the solid residue was dissolved in CH2Cl2 (5 mL) and fil-
tered to separate the catalyst. After evaporation of the sol-
vent, the residue was recrystallized from EtOH and water
(95:5) to afford the pure product.
Experimental
General
Chemicals were purchased from Fluka, Merck, Aldrich
Chemical Companies. Yields refer to isolated products. The
products were characterized by their physical constants,
comparison with authentic samples and IR and NMR spec-
troscopy. The purity determination of the substrate and
reaction monitoring were accomplished by TLC on silica
gel polygram SILG/UV 254 plates.
General procedure for the synthesis of bis(indolyl)
methanes
BiVO4-NPs (30 mg) was added to a mixture of indole and/
or 2-methyl indole (2 mmol) and the aldehyde compound
(1 mmol), and the mixture was stirred at 80 °C under sol-
vent-free conditions for the appropriate time. After comple-
tion of the reaction (monitored by TLC), the mixture was
diluted with 30 mL of hot ethanol and the catalyst was
recovered by filtration and washed with EtOH (5 mL). The
solvent was evaporated under reduced pressure, and the
remaining solid was recrystallized from a mixture of etha-
nol/water (95:5) to afford the pure products. All the prod-
ucts have spectral and physical data consistent with those
reported in the literature as well as the samples prepared
from previously reported methods.
Instrumentation
The FT-IR spectra were run on a VERTEX 70 Brucker
company (Germany). The 1HNMR (400 MHz) and
13CNMR (100 MHz) were run on a Bruker Avance DPX-
400 FT-NMR spectrometer in CDCl3 and DMSO-d6 using
TMS as an internal reference (δ in ppm). Melting points
were recorded on a Büchi B-545 apparatus in open capil-
lary tubes.
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J IRAN CHEM SOC
Table 1 Experimental conditions for the preparation of crystalline BiVO4 powder sample
Sample Amount of Bi(NO3)3·5H2O
Amount of NH4VO3
Experimental conditions
Autoclaving Calcination
at 170 °C
BiV-2 0.03 mol in 20 mL of 4 M HNO3
(homogeneous solution)
0.03 mol in 20 mL of 25 % (w/w) Each precursor stirred separately 130 h
–
aqueous solution of TMAH
(homogeneous solution)
for 2 h at RT, then mixed and
stirred for 30 min at RT
General procedure for the synthesis of DHPMs in the
absence of solvent
Figure 2 shows the SEM micrograph of sample BiV-2.
Sample BiV-2 consists of smaller irregular particles organ-
ized in larger aggregates and of bigger particles with well-
defined edges and planes.
A mixture of the aldehyde, oxime and/or acylal (1 mmol),
1,3-dicarbonyl compound (1 mmol), urea (or thiourea)
(1.2 mmol) and BiVO4-NPs (30 mg, 9.3 mol%) was heated
in an oil bath (120 °C) under solvent-free conditions. After
completion of the reaction (monitored by TLC), the reac-
tion mixture was cooled to room temperature and EtOH
(5 mL) was added and filtered to separate the catalyst. Then
the crude product was recrystallized from EtOH to give the
pure product.
Figure 3 shows the transmission electron micrographs of
samples BiV-2.
The IR band at ~1635 cm−1 corresponds to bend-
ing vibrations of adsorbed H2O molecules. These FI-IR
can berelated to the corresponding spectra of some other
(MVO4) formulated compounds (Fig. 4).
In addition, in this article for the first time, the accelera-
tion of the preparation of 3,4-dihydropyrimidin-2(1H)-ones
and -thiones from the protected derivatives of aldehydes
including oximes, semicarbazones and 1,1-diacetates in the
presence of BiVO4-NPs is reported.
General procedure for the synthesis of DHPMs
in EtOH
At the first step and in order to optimize the reaction
conditions, the prepared catalyst was used for the promo-
tion of the condensation of 4-chlorobenzaldehyde with
4-hydroxycoumarin and compared the effect of different
solvents and solvent-free conditions and also the effect of
the catalyst load on the reaction yield and time at thermal
conditions. The results are shown in Table 2.
On the basis of these results, it can be concluded that the
best results can be obtained under the conditions showed in
Scheme 1. It is important to note that using lower amounts of
the catalyst resulted in the products in longer reaction times.
To assess the efficiency of BiVO4-NPs in the prepara-
tion of biscoumarin derivatives, a wide range of aromatic,
aliphatic and heterocyclic aldehydes were reacted with
4-hydroxycoumarin under the optimal reaction conditions
and the obtained results are shown in Table 3.
It was observed that under the selected conditions, aro-
matic aldehydes containing electron-withdrawing groups
as well as electron-donating groups were easily reacted in
short reaction times with good to excellent isolated yields
(Table 3, entries 1–13). The reaction conditions were mild
enough to induce any damage to the acid-sensitive moieties
(Table 3, entries 8–10). α,β-Unsaturated aldehydes were
also reacting in high yields using this procedure without the
formation of any by-products (Table 3, entries 14, 15). In
addition, aliphatic aldehydes reacted very slowly under the
selected conditions (Table 3, entry 18).
A mixture of the semicarbazone (1 mmol), 1,3-dicarbonyl
compound (1 mmol), urea (or thiourea) (1.2 mmol) and
BiVO4-NPs (30 mg, 9.3 mol%) in EtOH (2 mL) was stirred
under reflux conditions. After completion of the reaction
(monitored by TLC), the mixture was cooled to room tem-
perature and filtered to separate the catalyst. Then the crude
product was recrystallized from EtOH to give the pure
product.
Results and discussion
In recent years, preparation and use of nano-catalysts in
organic transformations became an important part of our
ongoing research program [78–81]. In continuation of these
studies, among the four types of BiVO4 introduced by Gol-
mojdeh and Zanjanchi [77], we used BiV-2 as an efficient
and reusable nano-catalyst for the synthesis of biscou-
marins, bis(indolyl)methanes and dihydropyrimidinones
(thiones). All the reactions are performed under mild reac-
tion conditions in good to high yields.
Figure 1 shows the characteristic part of the X-ray of
sample BiV-2. These patterns show an excellent match with
the published JCPDS data (JCPDS file No. 14-0688) for
monoclinic BiVO4. These XRD maximums of very small
intensity are in the positions 2θ = 11.5, 23.3, 31.8 and
32.38 (Cu Ka radiation) and do not belong to the BiVO4
phase.
A plausible mechanism of the preparation of biscou-
marins is shown in Scheme 2 [16].
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J IRAN CHEM SOC
Fig. 1 XRD patterns of BiV-2
Fig. 4 FT-IR spectra of sample BiV-2, recorded at RT
Table 2 Effect of different solvents and different amounts of BiVO4-
NPs on the reaction of 4-chlorobenzaldehyde and 4-hydroxycou-
marina
Entry Conditions
BiVO4-NPs
(mg)
Time (min) Conversion (%)
1
2
3
4
H2O, 100 °C
H2O, 80 °C
H2O, 80 °C
20
30
20
30
180
47
100
100
100
0
105
50
Solvent-free,
80 °C
Fig. 2 SEM photograph of sample BiV-2
5
Solvent-free,
120 °C
30
60
20
6
7
CH2Cl2, 80 °C 30
CH3CN, 80 °C 30
50
60
0
20
a
Reaction conditions: 4-chlorobenzaldehyde (1 mmol), 4-hydroxy-
coumarin (2 mmol), H2O, 80 °C, BiVO4 (30 mg)
After successful synthesis of biscoumarins, we decided
to explicit the synthesis of bis(indolyl)methanes using
BiVO4-NPs as the catalyst.
In order to optimize the reaction conditions, we have stud-
ied the effect of BiVO4-NPs in the condensation of 4-chlo-
robenzaldehyde with indole as a model reaction. The reaction
was performed in different solvents and also under solvent-
free conditions, using different amounts of the catalyst at dif-
ferent temperatures. The results are shown in Table 5.
On the basis of this table, it can be concluded that the
best results can be obtained under the conditions shown in
Scheme 3.
After optimization of the reaction conditions and in
order to show the general applicability of the method, dif-
ferent types of aromatic aldehydes were subjected to the
same reaction under the determined conditions. The results
are summarized in Table 6.
Fig. 3 TEM micrographs of sample BiV-2
The reusability of this catalyst is exemplified by the
reaction of 4-chlorobenzaldehyde with 4-hydroxycoumarin
in the presence of the recycled reagent which gave the
requested product in 98 % yields after three runs (Fig. 5).
In order to show the efficiency of the present method,
we have compared our results obtained from the synthesis
of biscoumarins catalyzed by BiVO4-NPs with other results
reported in the literature. As shown in Table 4, some of the
previously reported methods are performed in the presence
of toxic reagents (Table 4, entry 3) or solvents (Table 4,
entries 6–8). In water and in the absence of the catalyst,
the reaction is proceeded in much longer reaction times
(Table 4, entry 1).
As shown in Table 6, various aromatic aldehydes
underwent smooth transformation to the corresponding
bis(indolyl)methanes in high, excellent yields. In addition,
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J IRAN CHEM SOC
Scheme 1 Synthesis of biscou-
marins using BiVO4-NPs as the
catalyst
Table 3 Preparation of
biscoumarins using BiVO4-NPs
as the catalyst
Entry
Aldehydes
Time (min)
Yield (%)a, b Mp (°C)
Found
Reported (References)
1
C6H5CHO
25
47
98
98
97
95
98
98
95
98
95
95
98
50
95
95
95
95
95
226–229
248–250
200–202
263–266
232–233
231–233
196–198
248–250
232–234
252–254
222–225
249–252
215–218
226–228
190–193
263–265
270–272
229–231 [82]
250 [83]
2
4-ClC6H4CHO
3
2-ClC6H4CHO
65
201–203 [82]
264–266 [23]
230 [83]
4
4-BrC6H4CHO
65
5
4-NO2C6H4CHO
3-NO2C6H4CHO
2-NO2C6H4CHO
4-MeOC6H4CHO
3-MeOC6H4CHO
2-MeOC6H4CHO
4-OHC6H4CHO
2-OHC6H4CHO
4-NMe2C6H4CHO
Cinnamaldehyde
2-Nitro cinnamaldehyde
Pyridin-4-carbaldehyde
Pyridin-3-carbaldehyde
35
6
60
229–231 [23]
198–200 [82]
250–252 [82]
238–240 [23]
258–260 [84]
228–230 [15]
254–256 [82]
222–224 [20]
230–232 [18]
190–192 [16]
261–263 [85]
274–276 [85]
7
90
8
90
9
75
10
11
12
13
14
15
16
17
80
115
80
85
110
180
35
50
a
Isolated yield
b
Reaction conditions: 4-chlorobenzaldehyde (1 mmol), 4-hydroxycoumarin (2 mmol), H2O, 80 °C,
BiVO4 (30 mg)
the present methodology is found to be applicable for the
preparation of bis(indolyl)methanes from 2-methylindole
and/or 5-bromo indole and aldehydes with excellent yield
(Table 6, entries 14–24).
The reaction of indole or 5-bromo indole with p-phthal-
dialdehyde and/or m-phthaldialdehyde (in a 4:1 ratio) in the
presence of BiVO4-NPs (60 mg) was also successful, and
the desired product was obtained after short reaction times
in high yields (Table 6, entries 12, 23, 24).
The preparation of tris(indolyl)methanes from the reac-
tion of 2-methyl indole with indole 3-carbaldehyde in the
presence of this catalyst was also examined. This reaction
was performed during acceptable reaction times in high
yields (Table 6, entry 18). Also, using this method, the
reaction of isatin with indole and/or 2-methylindole was
successful and the desired products were obtained in good
to high yields (Table 6, entries 13, 19).
drying at 70°C. The reusability of this catalyst is exempli-
fied by the reaction of 4-nitrobenzaldehyde with 2-methyl-
indole in the presence of the recycled reagent which gave
the requested product in 98, 98, 98, 94 and 90 % yields
after five runs (Fig. 6).
The possible mechanism of the synthesis of bis(indolyl)
methanes in the presence of BiVO4-NPs is shown in
Scheme 4 [46].
To illustrate the efficiency of the present method, Table 7
shows the comparison between our result obtained from the
reaction of indole with 4-chlorobenzaldehyde and the same
results reported by the other reagents in the literature.
It is important to note that, although some of these meth-
ods fulfilled under milder reaction conditions (room tem-
perature), they needed larger amounts of the catalyst for
completion (Table 7, entries 2, 4).
After the above-mentioned studies, we were interested to
study the accelerating effect of BiVO4-NPs in the Biginelli
reaction. In order to optimize the reaction conditions for
We have found that BiVO4-NPs is a very stable catalyst
and can be recycled by filtration, washing with acetone and
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J IRAN CHEM SOC
Scheme 2 A plausible mechanism for the synthesis of biscoumarins in the presence of BiVO4-NPs
Table 5 Effect of different solvents and different amounts of BiVO4-
NPs on the reaction of 4-chlorobenzaldehyde and indole
120
100
80
60
40
20
0
98
98
98
Yield
Entry Solvent
BiVO4-NPs (mg) Time (min) Conversion (%)
Time(min)
1
2
3
4
5
6
7
8
H2O
30
30
240
100
53
70
70
100
100
100
0
57
EtOH
47
47
Solvent-free 20
Solvent-free 30
Solvent-free 40
17
17
n-Hexane
CH2Cl2
30
30
30
60
60
0
1
2
3
CH3CN
60
0
Fig. 5 Reusability of BiVO4-NPs in the reaction of 4-chlorobenzal-
dehyde with 4-hydroxycoumarin
Reaction conditions: 4-chlorobenzaldehyde (1 mmol), indole
(2 mmol), solvent-free, 80 °C, BiVO4 (30 mg)
Table 4 Comparison of our
Entry
Catalyst (mol%) (References)
Reaction conditions
Time (h)
Yield (%)
results with some of the other
catalysts in the preparation of
biscoumarins
1
On-water [86]
H2O, 90 °C
4–5
93–98
55–70
91–99
75–95
82–95
90–96
85–91
87–93
80–96
90–98
75–95
95–98
2
HBF4 (10) [19]
H2O, 25 °C
10–12
0.33–0.53
0.42–0.58
0.42–0.67
0.5–0.8
0.5
3
I2 (10) [86]
H2O, 100 °C
H2O, 80 °C
4
RuCl3. nH2O (5) [16]
5
Tetrabutylammonium bromide (10) [19]
[P4VPy-BuSO3H]Cl-X(AlCl3) (7) [87]
NaHSO4.SiO2 (150 mg) [88]
Indion 190 resin (150 mg) [88]
SDS (20) [20]
H2O, 100 °C
Toluene, 90 °C
Toluene, 100 °C
Toluene, 100 °C
H2O, 60 °C
6
7
8
0.5
9
2.5–3
10
11
12
Phosphotungstic acid (15) [18]
BiVO4 (15) (this work)
BiVO4-NPs (9.3) (this work)
H2O, 80 °C
0.23–0.42
3–5
H2O, 80 °C
H2O, 80 °C
0.42–3
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J IRAN CHEM SOC
Scheme 3 Synthesis of
bis(indolyl)methanes using
BiVO4-NPs as the catalyst
Table 6 Synthesis of
bis(indolyl)methanes in the
presence of BiVO4-NPs
Entry Carbonyl compound
R1 R3 Time (min) Yield
(%)a, b
Mp (°C)
Found
Reported (References)
1
C6H5CHO
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
18
19
17
11
22
35
25
30
55
30
32
45
42
98
80
98
98
98
98
70
70
98
80
95
80
80
123–125 125–127 [56]
111–113 110–112 [89]
2
4-BrC6H4CHO
4-ClC6H4CHO
3-ClC6H4CHO
2-ClC6H4CHO
4-NO2C6H4CHO
3-NO2C6H4CHO
2-NO2C6H4CHO
4-OHC6H4CHO
4-MeOC6H4CHO
3-MeOC6H4CHO
1,4-C6H4(CHO)2
O
3
78–80
80–83
70–72
76–78 [56]
83–84 [90]
72–76 [89]
4
5
6
235–239 241–243 [91]
261–263 267–269 [91]
135–137 139–141 [92]
120–122 122–124 [89]
180–182 184–186 [91]
180–182 186–188 [91]
205–207 194 [58]
7
8
9
10
11
12
13
309–312 >300 [93]
O
N
H
14
15
16
17
18
19
C6H5CHO
Me
Me
Me
Me
H
H
H
H
H
H
5
5
98
98
98
98
90
90
178–180 180–183 [56]
180–182 180–184 [56]
240–242 240–242 [35]
236–239 237–239 [39]
270–272 270–272 [58]
300–302 300–301 [94]
4-ClC6H4CHO
4-NO2C6H4CHO
4-OHC6H4CHO
10
18
100
18
Indole-3-carbaldehyde Me
Me
O
O
N
H
20
21
22
23
24
C6H5CHO
H
H
H
H
H
Br
Br
80
25
85
228–230 230–232 [90]
140–143 145–147 [95]
218–219 219–221 [96]
175 dec. 180 dec. [95]
210 dec. 210 dec. [95]
4-ClC6H4CHO
70
4-NO2C6H4CHO
1,3-C6H4(CHO)2
1,4-C6H4(CHO)2
Br 100
Br 135
90
80c
90c
Br
65
a
Isolated yield
b
Reaction conditions: 4-chlorobenzaldehyde (1 mmol), indole (2 mmol), solvent-free, 80 °C BiVO4
(30 mg)
c
60 mg of the catalyst was used
this reaction, the condensation of 4-chlorobenzaldehyde,
ethyl acetoacetate and urea was studied in different condi-
tions in the presence of different amounts of BiVO4-NPs.
The obtained results showed that the reaction using
30 mg of the catalyst at 120 °C proceeded with highest
yield in shorter reaction times (Scheme 5).
1 3

J IRAN CHEM SOC
120
100
80
60
40
20
0
On the basis of these studies and after the successful
application of BiVO4-NPs in the preparation of DHPMs
from aldehydes, we attempted the Biginelli reaction using
acylals, oximes and semicarbazones as different protected
derivatives of aldehydes. To the best of our knowledge this
is the first example of use of oximes and semicarbazones
in this reaction. We have found that this method allows
the direct synthesis of 3,4-dihydropyrimidin-2(1H)-ones
from protected aldehydes without the need of deprotection
(Scheme 6).
Yield
98
98
98
94
90 90
Time(min)
45
20
12
10
1
2
3
4
5
It was observed that under the selected conditions,
oximes, semicarbazones and 1,1-diacetates containing
Fig. 6 Reusability of BiVO4-NPs in the reaction of 4-nitrobenzalde-
hyde with 2-methylindole
Table 7 Compared performance of various catalysts in the reaction
of indole and 4-chlorobenzaldehyde
To assess the efficiency of BiVO4-NPs in the prepara-
tion of 3,4-dihydropyrimidin-2(1H)-ones, various aromatic
aldehydes were employed to the same reaction under the
optimal conditions. The obtained results showed that these
conversions can occur with excellent yields in very short
times (Table 8, entries 1–13). Acetyl acetone and thiourea
can also be used with similar success to provide the corre-
sponding products (Table 8, entries 14–25).
In 2008, the first example of the Biginelli reaction
using acylals catalyzed by 12-tungstophosphoric acid was
reported by Khabazzadeh et al. [104]. Using this method,
the products were obtained in acceptable yields in the
absence of solvent under heating conditions. Although the
method is useful, the catalyst is not recoverable.
Entry Catalyst (mol%)
(References)
Conditions
Time
(h)
Yield
(%)
1
2
3
4
5
6
V(HSO4)3 (10) [57]
M(HSO4)x (100) [56]
TBATB (5) [34]
Solvent-free, 80 °C 0.66
85
EtOH, r.t.
2.5–7.5 89–91
MeOH, r.t.
1.5
0.5
2–4
85
92
82
P2O5/SiO2 (40) [40]
Solvent-free, r.t.
Squaric acid (8.6) [58] H2O, r.t.
[Et3NH][H2PO4] (200) Solvent-free,
5 min 84
30 min 90
60 min 85
[59]
100 °C
7
8
Silica sulfuric acid
(13) [84]
Solvent-free, r.t.
Bi(NO3)3.5H2O (20)
[97]
CH3CN, r.t.
9
BiVO4 (15) (this work) Solvent-free, 80 °C 1.5
85
In 2013, acylals were also used for the preparation
of DHPMs by Mohan et al. However, the products were
obtained in very long times (>15 h) [105].
10
BiVO4-NPs (9.3) (this Solvent-free, 80 °C 17 min 98
work)
Scheme 4 Proposed mechanism for the synthesis of bis(indolyl)methanes catalyzed by BiVO4-NPs
1 3

J IRAN CHEM SOC
Scheme 5 BiVO4-NPs catalyzed synthesis of 3,4-dihydropyrimidin-2(1H)-ones and -thiones
Table 8 Preparation of
Entry
R1
R2
X
Time(min)
Yield (%)a, b Mp (°C)
Found
3,4-dihydropyrimidin-2(1H)-
ones and -thiones using BiVO4-
NPs as the catalyst under
solvent-free conditions
Reported (References)
1
Ph
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OMe
OMe
OMe
Me
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
S
20
10
15
15
15
10
10
15
40
10
35
20
25
10
20
30
40
90
60
100
80
60
45
50
65
98
98
98
96
98
95
95
98
96
97
95
98
95
98
98
96
94
85
90
95
96
96
95
95
95
196–198
206–210
185–188
217–218
198–202
223–225
275–279
190–192
240–244
220–223
230–231
200–203
185–187
210–212
238–241
225–226
260–263
175–177
150–152
149–152
219–221
234–237
198–201
156–157
190–193
199–201 [67]
208–210 [67]
190–191 [67]
217–220 [67]
203–205 [67]
225–227 [67]
277–279 [67]
195–196 [67]
248–250 [98]
226–228 [99]
233–235 [99]
194–196 [100]
186–188 [100]
213–215 [67]
240–242 [67]
226–228 [67]
263–265 [67]
179–180 [67]
150–153 [67]
151–153 [101]
220–222 [102]
235–237 [67]
200–202 [103]
158–160 [103]
192–193 [103]
2
4-Cl-Ph
3
3-Cl-Ph
4
2-Cl-Ph
5
4-NO2-Ph
3-NO2-Ph
2-NO2-Ph
4-MeO-Ph
4-(Me)2N-Ph
4-OH-Ph
4-NO2-Ph
4-Cl-Ph
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
4-MeO-Ph
4-Cl-Ph
4-Br-Ph
Me
4-NO2-Ph
3-NO2-Ph
4-Cl-Ph
Me
Me
OEt
OEt
OEt
Me
4-MeO-Ph
4-(Me)2N-Ph
Ph
S
S
S
2-HO-Ph
4-HO-Ph
4-MeO-Ph
4-Cl-Ph
Me
S
Me
S
Me
S
Me
S
The desired products were characterized by their physical data, comparison with authentic samples, and IR
and NMR spectroscopy
a
Isolated yield
b
Reaction conditions: 4-chlorobenzaldehyde (1.0 mmol), urea (1.2 mmol), ethyl acetoacetate (1.2 mmol),
solvent-free, 120 °C, BiVO4 (9.3 mol%)
Scheme 6 Synthesis of 3,4-dihydropyrimidin-2(1H)-ones from the protected aldehydes
1 3

J IRAN CHEM SOC
Table 9 Preparation of 3,4-dihydropyrimidin-2(1H)-ones and -thiones from the reaction of protected aldehydes using BiVO4-NPs as the catalyst
Entry
Protected aldehyde
R2
X
Time (min)
Yield (%)a
Mp (°C)
Found
Reported (References)
1
4-Cl-PhCH=NOH
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OMe
Me
O
O
O
O
O
S
45
60
60
50
35
40
65
35
40
90
50
55
75
35
45
55
40
35
30
35
35
40
60
60
50
70
45
55
35
98
95
94
95
96
97
98
90
80
95
98
95
94
96
95
92
94
98
95
93
95
98
95
94
98
96
98
90
95
205–208
214–217
250–253
275–277
240–244
149–152
175–179
200–203
211–213
190–191
206–208
186–189
250–253
193–195
204–206
253–256
200–203
210–213
224–226
260–263
157–160
190–192
230–231
200–203
185–188
177–179
206–208
215–217
193–195
208–210 [67]
217–220 [67]
254–255 [101]
277–279 [67]
248–250 [98]
151–153 [101]
179–180 [67]
194–196 [100]
213–215 [67]
192–193 [103]
208–210 [67]
190–191 [67]
254–255 [101]
195–196 [67]
206–208 [101]
255–257 [106]
203–205 [67]
213–215 [67]
226–228 [67]
263–265 [67]
158–160 [103]
192–193 [103]
233–235 [99]
194–196 [100]
186–188 [100]
179–180 [67]
208–210 [67]
217–220 [67]
195–196 [67]
2
2-Cl-PhCH=NOH
3
2,4-Cl2-PhCH=NOH
4
2-NO2-PhCH=NOH
5
4-(Me)2N-PhCH=NOH
4-(Me)2N-PhCH=NOH
4-Cl-PhCH=NOH
6
7
S
8
4-Cl-PhCH=NOH
O
O
S
9
4-Cl-PhCH=NOH
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
4-Cl-PhCH=NOH
Me
4-Cl-PhCH=NNHCONH2
3-Cl-PhCH=NNHCONH2
2,4-Cl2-PhCH=NNHCONH2
4-MeO-PhCH=NNHCONH2
3-MeO-PhCH=NNHCONH2
2-MeO-PhCH=NNHCONH2
4-NO2-PhCH=NNHCONH2
4-Cl-PhCH=NNHCONH2
4-NO2-PhCH=NNHCONH2
3-NO2-PhCH=NNHCONH2
4-MeO-PhCH=NNHCONH2
4-Cl-PhCH=NNHCONH2
4-NO2-PhCH=NNHCONH2
4-Cl-PhCH=NNHCONH2
4-MeO-PhCH=NNHCONH2
4-Cl-PhCH=NNHCONH2
4-Cl-PhCH(OAc)2
OEt
OEt
OEt
OEt
OEt
OEt
OEt
Me
O
O
O
O
O
O
O
O
O
O
S
Me
Me
Me
Me
S
OMe
OMe
OMe
OEt
OEt
OEt
OEt
O
O
O
S
O
O
O
2-Cl-PhCH(OAc)2
4-MeO-PhCH(OAc)2
The desired products were characterized by their physical data, comparison with authentic samples, and IR and NMR spectroscopy
a
Isolated yield
b
Reaction conditions: oximes, semicarbazones and 1,1-diacetates (1.0 mmol), urea (1.2 mmol), ethyl acetoacetate (1.2 mmol), BiVO4
(9.3 mol%)
120
100
80
60
40
20
0
120
100
80
60
40
20
0
Yield
98
98
98
96
95
Yield
90
90
Time(min)
Time(min)
60
55
50
30
20
15
15
1
2
3
1
2
3
4
Fig. 8 Recyclability of the catalyst (Table 9, entry 25)
Fig. 7 Recyclability of the catalyst (Table 8, entry 5)
1 3

J IRAN CHEM SOC
Table 10 Comparison of the
results of the reaction of ethyl
acetoacetate, urea and PhCHO
using BiVO4-NPs with some of
those obtained in the presence
of the other reported nano-
catalysts
Entry
Catalyst (mol%)
Conditions
Time (h)
Yield (%)
1
Nano-ZnO (5) [67]
Solvent-free, 60 °C
Solvent-free, 80 °C
Solvent-free, 100 °C
Solvent-free, r.t.
EtOH, 363 K
10
0.266
2
95
2
Fe3O4 (20) [107]
90
3
Fe3O4@SiO2@Me&Et-PhSO3H (0.5) [108]
Fe3O4/PAA-SO3H (22.3) [109]
Fe3O4@SBA-15 (0.084) [110]
Nano-silica phosphoric acid (10.32) [111]
[Gmim]Cl-Cu(II) (0.0001) [112]
l-proline (10) [113]
90
4
2
90
5
6
85
6
Solvent-free, 80 °C
Solvent-free, 25
Water, reflux
2
91
7
12
8
94
8
Trace
Trace
92
9
SnCl2·2H2O (10) [113]
Water, reflux
48
1.5
4
10
11
12
Bi(NO3)3 (5) [114]
CH3CN, reflux
BiVO4 (15) [this work]
Solvent-free, 120 °C
Solvent-free, 120 °C
75
BiVO4-NPs (9.3) [this work]
0.33
98
electron-withdrawing groups as well as electron-donating
groups were easily reacted in short reaction times with
good to excellent isolated yields (Table 9, entries 1–29).
It is important to note that since the reaction of semicarba-
zones was not completed under the optimal conditions, these
compounds were reacted in EtOH under reflux conditions.
Also, obtained results indicated that the protected alde-
hydes reacted in longer times compared with the aldehydes
and all the Biginelli type reactions proceeded in very short
times with high yields.
catalyst in other organic transformations is in progress in
our laboratory.
Acknowledgments We are thankful to the University of Guilan
Research Council for the partial support of this work.
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