Zirconium oxide (NP) - Ionic liquid as an efficient media for the domino Knoevenagel hetero Diels-Alder reaction with unactivated alkynes

Article abstract of DOI:10.1016/j.crci.2011.12.002

Immobilized ZrO₂-nanopowder (NP) in ionic liquid and different organic solvents was used as a suitable Lewis-acid for the synthesis of polycyclic heterocycles which contains pyran-based skeletons. Reaction of O-propargylated salicylaldehyde wit

Full text of DOI:10.1016/j.crci.2011.12.002

C. R. Chimie 15 (2012) 283–289
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Full paper/Memoire
Zirconium oxide (NP) - ionic liquid as an efficient media for the domino
Knoevenagel hetero Diels-Alder reaction with unactivated alkynes
a
a
Saeed Balalaie a, , Ali Poursaeed , Malihe Javan Khoshkholgh ,
*
Hamid Reza Bijanzadeh b, Eckardt Wolf c
a Peptide Chemistry Research Center, K. N. Toosi University of Technology, P.O. Box 15875-4416, Tehran, Iran
b Department of Chemistry, Tarbiat Modares University, P. O. Box 14115-175, Tehran, Iran
c Tofigh Daru Res. & Eng. Co., 61st St. Km 18 Karaj Highway, Tehran, 37515-375, Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
Immobilized ZrO2-nanopowder (NP) in ionic liquid and different organic solvents was
used as a suitable Lewis-acid for the synthesis of polycyclic heterocycles which contains
pyran-based skeletons. Reaction of O-propargylated salicylaldehyde with active methy-
lene compounds in the presence of ZrO2-NP in ionic liquid proceeds via domino
Knoevenagel hetero Diels-Alder reaction of unactivated alkynes to construct the pyran
skeleton. Comparison with different ionic liquids and organic solvents showed that the
best results were obtained with 1-butyl-3-methylimidazolium nitrate [bmim][NO3]
because of short reaction times and high yields. Carrying out the reaction under these
conditions has advantages such as: high yields, short reaction times and easy work-up.
Received 2 August 2011
Accepted after revision 5 December 2011
Available online 4 January 2012
Dedicated to Prof. Mohammad Reza Saidi
on the occasion of his 65th birthday.
Keywords:
Ionic liquid in synthesis of heterocycles
ZrO2 nanopowder (ZrO2-NP)
Domino Knoevenagel hetero-Diels-Alder
reaction
´
ß 2012 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Unactivated alkynes
[bmim][NO3]
1. Introduction
In most reported domino Knoevenagel-hetero-Diels-
Alder reactions, alkenes were used as dienophile. The use
Synthesis of complex organic molecules with maxi-
mum synthetic efficiency in only very few steps is called an
ideal synthesis [1]. Domino reactions are powerful
synthetic tools to access complex molecules [2]. The
domino Knoevenegel-hetero-Diels-Alder reaction is one of
the most powerful methods for the preparation of
heterocyclic compounds and it has wide applications in
the synthesis of biologically active compounds to obtain
natural products which contain a pyran moiety [3]. These
processes are of great interest in diversity-oriented
syntheses, for example to generate compound libraries
for screening purposes [4].
of alkynes was limited due to their low reactivity
compared to alkenes [5]. The activation of alkynes toward
a variety of organic transformations is an interesting field
in organic synthesis [6]. The application of transition metal
catalysis is a common strategy for this purpose. Selection
of a suitable Lewis acid is very important. Among the metal
catalysts and, noble metals (some of them used for
coinage), e.g. copper, silver, and gold, and their derivatives
play an essential role in this activation [7,8]. Recently,
copper (I) salts have emerged as efficient Lewis acids for
various C–C and C–X bond formation and alkyne activation
reactions [9], and also for domino Knoevenagel-hetero-
Diels-Alder reactions [10].
Due to the importance of domino Knoevenagel-hetero-
Diels-Alder reactions and the extreme biological activities
of the synthesized products, optimizing the conditions
* Corresponding author.
E-mail address: balalaie@kntu.ac.ir (S. Balalaie).
1631-0748/$ – see front matter ß 2012 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.crci.2011.12.002

284
S. Balalaie et al. / C. R. Chimie 15 (2012) 283–289
X
X
O
X
ZrO2-NP
O
O
O
O
+
Solvent
Base
O
O
CHO
O
O
3a-m
2a-f
1a-f
[I]
Solvent = MeCN, H2O, EtOH, MeOH and [bmim][NO3]
Base = DAHP, Et3N
Scheme 1.
such as environmentally friendly, good to high yields,
lower reaction times, and mild reaction conditions are
parts of the necessary research in organic synthesis. As one
approach to achieve this goal, zirconium oxide nanopow-
der (ZrO2-NP) was checked for the use as an efficient
catalyst. Zirconium oxide (ZrO2) has special physical
properties such as hardness, high refractive index, optical
transparency, chemical and photoelectron stability [11]. To
the best of our knowledge, there is no report for a ZrO2
(especially ZrO2-NP)-application in the synthesis of
heterocyclic compounds.
One of the main principles of ‘‘green’’ chemistry is to
develop cost-effective and environmentally benign sys-
tems (most of them catalytic) which have become one of
the main themes of current synthetic chemistry. For
example, in this way, ionic liquids have been considered as
eco-friendly alternatives to volatile organic media because
of their negligible vapor pressure and nonflammable
nature [12]. Ionic liquids have been used as ‘‘green’’
reaction media in different organic reactions [13]. Herein,
we wish to report using of ZrO2 nanopowder as an efficient
Lewis acid for carrying out domino Knoevenagel-hetero-
Diels-Alder reaction of O-propargylated salicylaldehydes
which contain unactivated alkynes with active methylene
compounds in different organic solvents and in ionic liquid
as green media (Scheme 1).
pyran skeleton [10]. Initially, O-propargylated salicylal-
dehydes (1) as the starting material were prepared in
excellent yields using reaction of propargyl bromide and
salicylaldehyde derivatives in dimethylformamide and in
the presence of K2CO3. To optimize the desired reaction
conditions, the reaction of compound (1b) with dimethyl-
barbituric acid in acetonitrile and pyrazolone (2c) in
methanol were used as the model system. To optimize the
reaction conditions, we have used various metal catalysts
such as silver nanopowder, titanium dioxide nanopowder,
and scandium triflate. Among these catalysts, only the
ZrO2 for this reaction led good results (Table 1). According
to these results, ZrO2 was found to be a suitable Lewis acid.
The reactions were done using different ratios of ZrO2 in
the presence of different bases such as triethylamine,
diammonium hydrogen phosphate (DAHP). Reactions of
different active methylene compounds with O-propargyl
salicyclaldehydes using ZrO2 (20–40%) and in the pres-
ence of base were performed in water and other organic
solvents.
In all cases, our best result was obtained with 5-nitro-O-
propargylated salicylaldehyde (1b). To investigate the
effect of ionic liquids as a green media, the reaction of this
compound with 1-(3-chlorophenyl) pyrazolone (2c) as the
model reaction was done in different ionic liquids such as
n-butyl-and n-octyl-imidazolium salts (Scheme 2). The
results are summarized in Table 2. The best yields were
obtained with zirconium oxide (20%) in [bmim][NO3] as
reaction media.
2. Results and discussions
Carrying out the model reaction (Scheme 2) using
different ratios of ZrO2 showed that the best yields were
obtained using 20% ZrO2. It is clear that the reaction could
proceed in ionic liquid at room temperature in a short
reaction time (5 min) and also high yields (entry 1, Table 2).
By optimizing the base with different ratios of
triethylamine (10, 20, 30, 40%), the desired products were
obtained after 5 min in 80, 90, 95, and 95% yields,
respectively. The best yield and short reaction time was
obtained with [bmim][NO3] as reaction media. The results
with different active methylene compounds, ratios of ZrO2
and base and the structure of compounds with pyran
skeleton are summarized in Table 3.
In our recent research work, we surveyed different
domino Knoevenagel-hetero-Diels-Alder reactions with
unactivated alkynes using cuprous iodide for construction
of different heterocyclic compounds which contained the
Table 1
Effect of different reagents on the domino Knoevenagel-hetero-Diels-
Alder reaction of (1b) with dimethyl barbituric acid.
Reagent (40%)
Time (h)
Yield (%)
Ag (Nanopowder)
Sc (OTf)3
TiO2
48
48
48
6
–
–
–
Using the optimized conditions, we next explored the
scope and generality of the zirconium oxide nanopowder
ZrO2
48

S. Balalaie et al. / C. R. Chimie 15 (2012) 283–289
285
O2N
O
O2N
CHO
O
Ionic Liquid
r.t.
N
N
N
O
N
O
ZrO2 (20%)
Et3N (20%)
Cl
Cl
1b
3h
2c
Scheme 2.
in ionic liquids influence. The reactions were checked with
different active methylene compounds; such as barbituric
acid, dimethyl barbituric acid, indandione, pyrazolone, and
Meldrum’s acid. When babituric acid and Meldrum’s acid
were used as active methylene compound, 40% ZrO2 was
used. The experimental results are summarized in Table 3.
In entry 6, when the substrate 1d was treated with
pyrazolone 2c in MeOH in the presence of ZrO2 (NP) at
reflux condition for 6 h, the desired product 3f was
obtained in 80% overall yield. We also repeated the same
reaction in [bmim][NO3] at room temperature for 5 min
and the yield of desired product was obtained in 95% yield.
The same reaction with CuI needed more than 8 h in
refluxing MeOH.
methyl group with 2c (Scheme 3). Reaction of compound
(4) with aryl pyrazolone (2c) in the presence of zirconium
oxide (NP) at the same condition as previously mentioned
(Scheme 3) afforded product 5 in 60% yield.
We have also examined the reusability of the catalyst
system. Since [bmim][NO3] was soluble in water, it can
be separated from reaction medium by washing with
water, then extraction with EtOAc, dried at 80 8C under
reduced pressure and reused for the further reactions.
Although we did not carry out reactions with several
batches of the recovered catalyst, the repetition with one
batch indicated that its efficiency is similar to that of the
first time. For every reaction per 1 mmol, 1 ml of ionic
liquid was used.
Carrying out the reaction in ionic liquid only did not
lead to the desired product. The combination of ionic liquid
and zirconium oxide (NP) seems to be an efficient reaction
media for this synthesis.
In all cases, the structures of the products were
confirmed by their spectroscopic data. In 1H-NMR spectra
of the products, the –OCH2 group resonates in region
In conclusion, we have developed a novel and efficient
protocol for the synthesis of polycyclic compounds
containing the pyran skeleton. Combination of zirconium
oxide and ionic liquid has an important role in domino
Knoevenagel-hetero-Diels-Alder reaction. High yields, low
reaction times, carrying out the reaction at room
temperature, and easy set-up and work-up are advantages
of this method compared to reported methods.
The combined use of ionic liquids and zirconium oxide
nanoparticles for the synthesis of heterocyclic compounds
contained pyran skeleton offers great potential for rapid
and easily accessible developments in this area, due to the
efficient, economical and easily performed operations.
Intensive studies in this area are in progress in our
laboratory.
d
= 4.50–5.00 ppm as two distinguished doublets with
J = 11.5–11.8 Hz. The –CH proton appears as a singlet at
4.70–4.95 ppm. The alkene peak resonates at = 7.10–
d
d
7.30 ppm as a singlet. The corresponding signal of the –
OCH2 and the shielded alkene carbons in 13C-NMR appear
at
d
64–68 ppm and 83–90 ppm.
In our research study, our attention was focused on
intramolecular oxa-Diels-Alder reaction of different het-
erodienes with unactivated terminal acetylenes in the
presence of zirconium oxide as Lewis acid. We assume that
ZrO2 activates the triple bond. To check this assumption,
we reacted 4 in which the acetylenic protonis replaced by a
3. Experimental
In all experiments, ZrO2 (5–25 nm, Plasma Chem
GmbH) was used.
3.1. Method A (solvent): general procedure for the synthesis
Table 2
of compounds 3a–m
Influence of different ionic liquid in the synthesis of pyrano[2,3-
d]pyrimidine-1,3(2H)-dione.
A solution of propargylated salicyclaldehyde (1 mmol),
active methylene compound (1.2 mmol), ZrO2 (0.2 or 0.4
equiv.) and specified base Et3N or DAHP (0.2 equiv.) in
specified solvent was refluxed for 6-54 h (Table 3). The
progress of reaction was monitored by TLC (Eluent
Petroleum: EtOAc 3:2). The precipitated solid was filtered,
washed with cold ethanol and recrystallizated in dichlor-
omethane or acetonitrile.
Entry
Solvent
Yield%
Time (min)
1
2
3
4
5
6
7
[bmim][NO3]
[bmim][BF4]
[hmim][PF6]
[hmim][BF4]
[omim][SCN]
[omim][NO3]
[omim][Cl]
95
95
90
90
95
95
95
5
60
165
90
10
10
15

286
S. Balalaie et al. / C. R. Chimie 15 (2012) 283–289
Br
O
O
Br
CHO
ZrO2 -NP
N
N
Et3N
[bmim][NO3]
O
N
O
Cl
N
r.t
Cl
5
2c
4
Scheme 3. Reaction of pyrazolone 2c and O-propargyloxybenzaldehyde 4 for the synthesis of 5.
Table 3
Synthesis of polycyclic compounds contained pyran skeleton.
Entry Substrates
Products
ZrO2 (%)a,bZrO2 (%)a,b,c
CuI (%)a,b
Solvent
Basea
[bmim][NO3]
Yieldd% Solvent Time (min) Yieldd% Time (min) Yield% Time (h)
O
N
CHO
N
1
90a
80a
81b
CH3CN 600
90
95
80
30
20
50
80a
80a
81b
10
DAHP10b
O
O
O
OMe
1a
2a
3a
O
N
O
N
2
CHO
O
N
2
CH3CN 360
6
DAHP10b
O
O
1b
2a
3b
O
O2N
CHO
O
H
O
N
3
H2O
240
6
DAHP10a
N
H
O
1b
2b
3c
3d
O
Br
CHO
O
H
N
4
77b
H2O
1440
80
85
76b
30
DAHP10a
O
N
H
O
1c
2b

S. Balalaie et al. / C. R. Chimie 15 (2012) 283–289
287
Table 3 (Continued )
Entry Substrates
Products
ZrO2 (%)a,bZrO2 (%)a,b,c
CuI (%)a,b
Solvent
Basea
[bmim][NO3]
Yieldd% Solvent Time (min) Yieldd% Time (min) Yield% Time (h)
O
CHO
H
O
N
5
6
7
75b
80a
80a
H2O
1320
81
95
95
75
73b
80a
81a
28
DAHP10a
Et3N10d
Et3N10d
O
N
H
O
1d
2b
3e
N
O
CHO
O
N
MeOH
360
5
8
Cl
1d
2c
3f
3g
3h
3i
N
O
Me
CHO
N
MeOH
360
50
8
O
Cl
1e
2c
N
O2N
CHO
O
O
N
8
90a
90a
85a
80a
MeOH
MeOH
EtOH
360
360
600
1500
95
95
90
85
5
89a
80a
81a
80a
8
Et3N10d
Et3N10d
DAHP10c
DAHP10c
Cl
1b
2c
Cl
CHO
O
N
O
N
9
50
8
Ph
Cl
1f
2d
O
O
O2N
O
10
2–3
15
CHO
1b
2e
3j
O
O
11
EtOH
2–3
48
O
CHO
1d
2e
3k

288
S. Balalaie et al. / C. R. Chimie 15 (2012) 283–289
Table 3 (Continued )
Entry Substrates
Products
ZrO2 (%)a,bZrO2 (%)a,b,c
CuI (%)a,b
Solvent
Basea
[bmim][NO3]
Yieldd% Solvent Time (min) Yieldd% Time (min) Yield% Time (h)
O
O
Br
80a
EtOH
1440
85
2–3
70a
54
DAHP10c
O
12
CHO
1c
2e
3l
O
O
O
O
O2N
CHO
O
O
O
HOOC
13
MeCN
2400
90
50
81b
48
DAHP10e
O
81b
1b
2f
O2N
3m
a
All reactions were carried out using 20% mol of ZrO2.
All reactions were carried out using 40% mol of ZrO2.
b
c
Reactions with [bmim][NO3] were carried out at room temperature.
Isolated yields.
d
3.2. Method B (ionic liquid): general procedure for the
4.97 (s, 2H, OCH and –CH), 5.01 (s, 1H, OCH), 7.00 (d,
J = 9.0 Hz, 1H, HAr), 7.24 (s, 1H, = CH), 7.37 (dd, J = 6.5, 1 Hz,
1H, HAr), 7.51 (t, J = 8.0 Hz, 1H, HAr), 7.67 (dd, J = 8.1 Hz, 1H,
synthesis of compounds 3a–m
A solution of propargylated salicyclaldehyde (1 mmol),
active methylene compound (1.2 mmol), ZrO2 (0.2 or 0.4
equiv.) and specified base Et3N or DAHP (0.2 equiv.) in 1 ml
of Ionic liquid [bmim][NO3]was stirred for 5–40 min at
room temperature (Table 3). The progress of reaction was
monitored by TLC (Eluent Petroleum: EtOAc 3:2). After
completion of reaction, Water (10 mL) was added to the
mixture and the mixture was extracted with EtOAc. The
organic phase was separated and was dried with anhy-
drous natrium sulphate. The solvent was evaporated under
vacuum. The desired products were obtained in 80-95%
yields. For some cases, further purification was done using
n-hexane/dichloromethane.
H
Ar), 7.74 (t, J = 2.0 Hz, 1H, HAr), 7.87 (d, J = 1.8, 1H, HAr),
8.05 (dd, J = 9.0, 2.8 Hz, 1H, HAr); 13C-NMR (125 MHz,
DMSO-d6): = 13.9, 30.6, 66.3, 67.6, 95.5, 108.3, 117.8,
d
118.7, 119.9, 121.9, 124.1, 126.2, 127.7, 131.0, 133.6, 136.9,
138.5, 140.3, 145.9, 146.6, 159.2; HR-MS (EI):
C
C
20H14N3O435Cl [M]+ꢁ found 395.0663, cal. 395.0673,
20H14N3O437Cl [M+2]+ found 397.0622, cal. 397.0643.
3.3.3. Compound 3k
m.p. 183–184 8C; IR (KBr, cmꢀ1):
v
¼ 1703; 1588, 1490,
˜
1458; 1H-NMR (300 MHz, DMSO-d6): 4.61 (d, 1H,
J = 11.6 Hz, –OCH), 4.66 (d, 1H, J = 11.6 Hz, –OCH), 4.7 (s,
1H, CH), 6.78 (d, 1H, J = 8.1 Hz, H-Ar), 6.86 (brs, 1H, = CH),
6.89 (t, 1H, J = 7.5 Hz, HAr), 7.13 (t, 1H, J = 7.7 Hz, HAr), 7.19
(d, 1H, J = 6.6 Hz, HAr), 7.34–7.39 (m, 2H, HAr), 7.53 (d, 1H,
J = 7.2 Hz, HAr), 7.7 (d, 1H, J = 7.8 Hz, HAr); 13C-NMR
(75 MHz, DMSO-d6): 29.1, 65.4, 107.6, 112.9, 116.7,
118.7, 120.6, 121.5, 125.5, 128.0, 128.2, 130.8, 131.0,
133.1, 135.6, 136.9, 153.4, 169.5; HRMS (EI): Cal. for
3.3. Selected spectroscopic data
3.3.1. Compound 3b
˜
m.p. 254–255 8C; IR (KBr, cmꢀ1):
v
¼ 1704; 1638, 1521,
1340. 1H NMR (300 MHz, DMSO-d6):
d = 3.27 (s, 3H, NMe),
3.30 (s, 3H, NMe), 4.77 (s, 1H, CH), 4.86 (d, J = 11.6 Hz, 1H,
OCH), 4.98 (d, J = 11.6 Hz, 1H, OCH), 6.95 (d, J = 9.0 Hz, 1H,
C19H12O3: 288.0786, found: 288.0789.
H
Ar), 7.18 (s, 1H, = CH), 7.97 (s, 1H, HAr), 8.02 (d, J = 8.0 Hz,
3.3.4. Compound 3d
1H, HAr); 13C-NMR (75 MHz, DMSO-d6):
d
= 28.6, 29.5, 30.0,
m.p. 295–297 8C; IR (KBr, cmꢀ1):
¼ 3115; 3004, 1699,
˜
v
67.6, 85.2, 111.0, 118.0, 124.0, 124.5, 128.0, 136.4, 140.8,
150.5, 154.4, 159.8, 163.6; HR-MS (EI): C16H13N3O6 [M]+
found 343.0805, cal. 343.0804. Elemental analysis
(C16H13N3O6): cal. C 55.98, H 3.82, N 12.24, found C
55.75, H 3.69, N 12.08%.
1627. 1H-NMR (500 MHz, DMSO-d6):
d = 4.56 (s, 1H, –CH),
4.67 (d, J = 11.5 Hz, 1H, OCH), 4.78; (d, J = 11.5 Hz, 1H,
OCH), 6.71 (d, J = 8.7 Hz, 1H, HAr), 7.04 (s, 1H, = CH), 7.23 (s,
1H, HAr), 7.25 (d, J = 8.7 Hz, 1H, HAr), 11.28 (s, 1H, NH),
11.90 (s, 1H, NH); HR-MS (EI): C14H9N2O479Br [M]+
found 347.9710, cal. 347.9746; C14H9N2O481Br [M+2]+
found 349.9692, cal. 347.9725; Elemental analysis
(C14H9N2O4Br): cal. C 48.16, H 2.60, N 8.02, found C
48.07, H 2.53, N 7.96%.
3.3.2. Compound 3i
˜
1510; 1H-NMR (500 MHz, DMSO-d6):
m.p. 215–216 8C; IR (KBr, cmꢀ1):
v
¼ 1686; 1599, 1580,
= 2.48 (s, 3H, Me),
d

S. Balalaie et al. / C. R. Chimie 15 (2012) 283–289
289
[7] (a) Y. Liu, F. Song, Z. Song, M. Liu, B. Yan, Org. Lett. 7 (2005) 5409;
3.3.5. Compound 3m
(b) C. Bruneau, Angew. Chem. Int. Ed. 44 (2005) 2328;
(c) N. Asao, K. Sato, Y. Yamamoto, J. Org. Chem. 70 (2005) 3682;
(d) N. Asao, K. Takashi, S. Lee, T. Kasahara, Y. Yamamoto, J. Am. Chem.
Soc. 124 (2002) 12650;
(e) T. Shibata, Y. Ueno, K. Kanda, Synlett (2006) 411;
(f) N. Asao, S. Yudha, T. Nogami, Y. Yamamoto, Angew. Chem. Int. Ed. 44
(2005) 5526.
m.p. 242–243 8C; IR (KBr, cmꢀ1):
v
¼ 3407; 1782, 1680;
d = 2.49–2.62 (m, 1H, H-
˜
1H-NMR (300 MHz, DMSO-d6):
10b), 3.32–3.43 (m, 1H, H-1), 4.16 (dd, J = 13.3, 4.4 Hz, 1H,
H-1), 4.56 (d, J = 12.3 Hz, 1H, H-5), 4.84 (d, J = 12.3 Hz, 1H,
H-5), 7.07 (d, J = 8.5 Hz, 2H, H-7, H-4), 8.03 (dd, J = 8.5,
2.3 Hz, 1H, H-8), 8.33 (d, J = 2.3 Hz, 1H, H-10); 13C-NMR
[8] (a) C.S. Yi, S.Y. Yun, J. Am. Chem. Soc. 127 (2005) 1700;
(b) D.S. Ermolat’ev, V.P. Mehta, E.V. Eycken, Synlett (2007) 3117;
(c) T. Godet, C. Vaxelaie, C. Michel, A. Milet, P. Belmont, Chem. Eur. J. 13
(2007) 5632;
(d) Y. Xiao, J. Zhang, Angew. Chem. Int. Ed. 47 (2008) 1903;
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[9] (a) N. Asao, T. Kasahara, Y. Yamamoto, Angew. Chem. Int. Ed. 42 (2003)
3504;
(75 MHz, DMSO-d6):
d = 28.4, 34.4, 64.2, 111.9, 118.0,
123.6, 124.7, 124.8, 138.1, 141.2, 159.2, 167.0; HR-MS
(70 eV, EI) C12H9O5N m/z (%): 247 (M+, 72), 230 (100), 219
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Acknowledgment
We thank gratefully Iran National Science Foundation
(INSF) for their financial support. We are also grateful to
Prof. R. Gleiter for his invaluable comments. We express our
gratitude to Mr. M. Jalilevand, managing director of Kimia
Exir Company for chemical donation and financial support.
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