Efficient and ecofriendly route for the solvent-free synthesis of 4-alkoxy-5 H-chromen[2,3-d[pyrimidines using phosphonic acid functionalized KIT-6 confined ionic liquid as recoverable catalyst

Article abstract of DOI:10.1080/00397911.2014.916722

Phosphonic acid functionalized KIT-6 confined ionic liquid (IL, 1-butyl-3-methylimidazolium tetrafluoroborate [BMIm][BF4]) catalyzed the one-pot condensation reaction of iminochromenes and salicylaldehydes with different primary alcohols to achieve the co

Full text of DOI:10.1080/00397911.2014.916722

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Efficient and Ecofriendly Route for the
Solvent-Free Synthesis of 4-Alkoxy-5H-
chromen[2,3-d]pyrimidines Using
Phosphonic Acid Functionalized KIT-6
Confined Ionic Liquid as Recoverable
Catalyst
Nastaran Karimi a , Hoda Yahyavi b , Leila Ma'mani a , Mohammad
Mahdavi a , Alireza Foroumadi a c & Abbas Shafiee d
a Pharmaceutical Sciences Research Center , Tehran University of
Medical Sciences , Tehran , Iran
b Department of Chemistry, School of Sciences , Alzahra University ,
Vanak , Tehran , Iran
c Drug Design and Development Research Center, Faculty of
Pharmacy , Tehran University of Medical Sciences , Tehran , Iran
d Department of Medicinal Chemistry, Faculty of Pharmacy and
Pharmaceutical Sciences Research Center , Tehran University of
Medical Sciences , Tehran , Iran
Accepted author version posted online: 05 Jun 2014.Published
online: 28 Jul 2014.
To cite this article: Nastaran Karimi , Hoda Yahyavi , Leila Ma'mani , Mohammad Mahdavi ,
Alireza Foroumadi & Abbas Shafiee (2014) Efficient and Ecofriendly Route for the Solvent-Free
Synthesis of 4-Alkoxy-5H-chromen[2,3-d]pyrimidines Using Phosphonic Acid Functionalized KIT-6
Confined Ionic Liquid as Recoverable Catalyst, Synthetic Communications: An International
Journal for Rapid Communication of Synthetic Organic Chemistry, 44:19, 2826-2837, DOI:
10.1080/00397911.2014.916722
To link to this article: http://dx.doi.org/10.1080/00397911.2014.916722
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Synthetic Communications1, 44: 2826–2837, 2014
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2014.916722
EFFICIENT AND ECOFRIENDLY ROUTE FOR THE
SOLVENT-FREE SYNTHESIS OF 4-ALKOXY-5H-
CHROMEN[2,3-d]PYRIMIDINES USING PHOSPHONIC
ACID FUNCTIONALIZED KIT-6 CONFINED IONIC
LIQUID AS RECOVERABLE CATALYST
Nastaran Karimi,1 Hoda Yahyavi,2 Leila Ma’mani,1
Mohammad Mahdavi,1 Alireza Foroumadi,1,3 and
Abbas Shafiee4
1Pharmaceutical Sciences Research Center, Tehran University of
Medical Sciences, Tehran, Iran
2Department of Chemistry, School of Sciences, Alzahra University,
Vanak, Tehran, Iran
3Drug Design and Development Research Center, Faculty of Pharmacy,
Tehran University of Medical Sciences, Tehran, Iran
4Department of Medicinal Chemistry, Faculty of Pharmacy and
Pharmaceutical Sciences Research Center, Tehran University of
Medical Sciences, Tehran, Iran
GRAPHICAL ABSTRACT
Abstract Phosphonic acid functionalized KIT-6 confined ionic liquid (IL, 1-butyl-3-methy-
limidazolium tetrafluoroborate [BMIm][BF4]) catalyzed the one-pot condensation reac-
tion of iminochromenes and salicylaldehydes with different primary alcohols to achieve
Received December 20, 2013.
Address correspondence to Abbas Shafiee, Department of Medicinal Chemistry, Faculty of
Pharmacy and Pharmaceutical Sciences Research Center, Tehran University of Medical Sciences,
Tehran 14176, Iran. E-mail: shafiee@ams.ac.ir
Color versions of one or more of the figures in the article can be found online at www.tandfonline.
com/lsyc.
2826

IL@[PHOSPHONICACID@KIT-6]: GREEN CATALYST
2827
the corresponding 4-alkoxy-5H-chromen[2,3-d]pyrimidines under solvent-free conditions
and in good yields. This efficient nanocatalyst can be recovered for at least five reaction runs
without significant loss of either activity or confined IL.
Keywords 4-Alkoxy-5H-chromen[2,3-d]pyrimidines; KIT-6 confined ionic liquid;
one-pot synthesis; phosphonic acid functionalized KIT-6
INTRODUCTION
Multicomponent reactions (MCRs) have emerged as invaluable tools in the
drug discovery process in a one-pot synthetic operation. MCRs include two or more
steps without any isolation of intermediates, which reduce time and save both energy
and raw materials.[1] These techniques permit fast, automated, economical, and high-
throughput synthesis of the libraries of pharmaceutical and organic compounds.
Because of the diverse applications of the fluorescent compounds in biochemical
and medical research,[2] new multicomponent synthetic approaches to obtain these
compounds have received much attention. There are various synthetic strategies
for the synthesis of pyrimidine derivatives,[3] some of which report the reaction of
iminocoumarines in alcoholic solvents. In most of these reports, amines applied as
nucleophiles and ultimately amino-5H-chromeno[2,3-d]pyrimidine-2-yl-phenols were
obtained as major products. First, Costa and coworkers reported the synthesis of
dimeric chromene derivatives via the condensation of salicylaldehyde and malononi-
trile in the CH3OH and H2O media.[4] They realized that during the dimerization
process, CH3OH as well as malononitrile attacked the intermediate as a nucleophile.
According to our interest for the synthesis of pyrimidine derivatives, we tried to use
alcohols as reactant for the synthesis of new pyrimidine derivatives. Therefore, due
to the low nucleophylic property of alcohols, it was observed a suitable opportunity
for solid acid catalysts. Recently ZnCl2 was reported as a Lewis acid catalyst for
the synthesis of 4-methoxy-5H-chromeno[2,3-d]pyrimidine derivatives.[5]
Recently, the utilization of ionic liquids (ILs) as green solvents for the labora-
tory as well as industrial applications has been reported. The favorable and unique
properties such as low volatility, nonflammability, tunable polarity, miscibility with
organic and inorganic compounds, and the ease of recycling process are the most
important reasons for the widespread applications of ILs.[6] The most popular ILs
are the incorporation of different alkylated imidazolium- or phosphonium-based
cations with different anions such as tetrafluoroborate, hexafluorophosphate,
etc.[7] In the past decade, the physiochemical properties of confined ILs within hybrid
materials and their applications have been reported.[8] For example, a series of
functionalized mesoporous silica confined ILs were prepared and applied as catalyst.
The confinement effects studied and the results showed that filling meso-channels of
mesoporous with ILs improved the catalyst performance and selectivity in different
organic transformations. Over the past few years, the functionalized mesoporous
silicas confined ILs have been reported as more efficient catalysts in different organic
transformations.[9]
By virtue of the pivotal character of mesoporous silica nanoparticles (MSNs),
they have increasingly proven to be an extremely effective support for the immobi-
lization of a comprehensive range of homogeneous catalysts[10] and enzymes.[11] The

2828
N. KARIMI ET AL.
three-dimensional cubic Ia3d MSNs, having two interpenetrating continuous
networks of chiral channels, provide highly opened nanoporous hosts with simple
access for the guests and facilitating mass transfer through the channels.[12] KIT-6,
composed of two interwoven nanochannels similar to that found in MCM-48,[13]
was introduced as a promising candidate for the potential applications in hybrid
catalyst generation and enzyme immobilization.[14,15] On the other hand, the rela-
tively mild acidic behavior of phosphonic acid compared to stronger Brønsted acids
such as H2SO4 may make it less prone to promotion of side reactions. Moreover,
during recent years, phosphonic acid functionalized materials have been applied
in the various fields such as bioelectrochemistry, electroanalysis, and biomimetic
membranes.[16]
Following our previous research on multicomponent reactions and nano-
catalysts,[17] it was of interest to investigate novel approaches for the synthesis of
fluorescent chromenopyrimidine derivatives. Therefore, we report phosphonic
acid functionalized KIT-6 confined ionic liquid [BMIm][BF4], IL@[phosphonic
acid@KIT-6], as a recoverable nanocatalyst and promoter for the green synthesis
of 4-methoxy-5H-chromen[2,3-d] pyrimidine derivatives.
RESULTS AND DISCUSSION
In the present study, we designed and prepared KIT-6-functionalized phos-
phonic acid confined IL, IL@[phosphonicacid@KIT-6], as a promising candidate
to catalyze different organic conversions. To this purpose, the silica framework
KIT-6 has been synthesized via co-condensation of TEOS in the presence of the
structure-directing agents under acidic conditions, and its surface was furnished by
the covalent linkage of aminopropyl using 3-aminopropyl trimethoxysilane
(APTMS).[18] Then phosphonic acid was incorporated into amine ends using
Scheme 1. Synthesis of [phosphonicacid@KIT-6] and IL@[phosphonicacid@KIT-6].

IL@[PHOSPHONICACID@KIT-6]: GREEN CATALYST
2829
a straightforward Mannich-type reaction[19] between phosphorous acid and imine
(from reaction between primary amine in aminopropyl functionalized KIT-6 and
formaldehyde) in the presence of excess amount of concentrated HCl. Then
the IL@[phosphonicacid@KIT-6] was prepared by filling the 3D mesochannels of
phosphonic acid functionalized KIT-6 with [BMIm][BF4] (Scheme 1).
The catalyst was comprehensively characterized by x-ray powder diffraction
(XRD), N2 adsorption–desorption analysis, Fourier transform–infrared (FT-IR),
thermal gravimetric analysis (TGA), transmission electron microscopy (TEM),
and scanning electron microscopy (SEM) (see the supplementary data). SEM
and TEM recognize the ordered cubically honeycomb-like network with uniform
mesochannels and morphology of the mesoporous solid KIT-6 (Fig. 1). The average
pore diameter, which estimated from the TEM images, was about 7.5 nm, which
agreed well with that from the N2 sorption and XRD analysis.[19,20]
Figure 1. TEM image KIT-6 and N2 sorption isotherm experiment of nanocatalyst in the subsequent
modification process.

2830
N. KARIMI ET AL.
Scheme 2. Synthesis of iminochromenes (3) via tandem Knoevenagel and Pinner condensations.
Then the potential efficiency of [BMIm][BF4]@[phosphonicacid@KIT-6] as an
organic–inorganic nanohybrid catalyst was assessed in the synthesis of 4-alkoxy-5H-
chromen[2,3-d]pyrimidines under different conditions. The catalytic performance
and selectivity of [BMIm][BF4]@[phosphonicacid@KIT-6] was evaluated in the
synthesis of 4-methoxy-5H-chromen[2,3-d]pyrimidines via the three-component
condensation between 2-imino-2H-chromene-3-carbonitrile, salicylaldehyde, and
malononitrile as a model reaction. To this purpose, the required iminochromenes
(3a–c) were prepared based on Knoevenagel condensation of salicylaldehydes (1a–
c) and malononitrile (2) using the known procedure (Scheme 2).[21] To explore the
generality of the present protocol, we applied various iminochromenes and alcohols,
which led to a series of biologically interesting 4-alkoxy-5H-chromene[2,3-d]pyrimi-
dines under optimum mild condition. Results are listed in Table 1.
To illustrate the efficiency of this catalytic system, its ability was compared
with different Lewis and Brønsted acids (Table 2). This clearly indicated that
[BMIm][BF4]@[phosphonicacid@KIT-6] could be introduced as the best catalyst
for the aforementioned purpose. In
a separate experiment, the use of
[phosphonicacid@KIT-6] as a catalyst has worse results. This demonstrates the ben-
eficial role of the ionic liquid in obtaining acceptable conversions.
Based on the best of our knowledge, this investigation presents the first report
of an ecosafe and efficient synthesis of 4-alkoxy-5H-chromene[2,3-d]pyrimidines. On
the other hand, our method not only provides better yields in mild condition and
reduced reaction times but also introduces recyclable Brønsted acid functionalized
three-dimensional cubic Ia3d MSNs. Although the exact mechanism for the later
reaction has not been established, it is reasonable to propose that product 5 results
by nucleophilic attack of alcohol 4 to the obtained product 3 from the tandem
Knoevenagel and Pinner reactions (Scheme 2) to produce intermediate 6. Finally,
the intermediate 6 reacted with salicylic aldehyde, followed by proton transfer
to obtain the product 5 (Scheme 3).
Finally, to determine the applicability of catalyst recovery, the reaction mixture
was filtered off and the remaining catalyst was washed to remove the probable
residual product, dried under vacuum, and reused in subsequent runs. In five
consecutive runs, the conversion stayed with no detectable loss (1st run: 90%, 1st
reuse 89%, 2nd reuse: 90%, 3rd reuse: 88%, 4th reuse: 86%, Fig. 2), and the recovery
yield of IL@[phosphonicacid@KIT-6] was more than 92%.
To explore the high potent and efficiency of this catalyst, we evaluated
[BMIm][BF4]@[phosphonicacid@KIT-6] as catalyst in the one-pot condensation

IL@[PHOSPHONICACID@KIT-6]: GREEN CATALYST
2831
Table 1. Synthesis of 4-alkoxy-5H-chromen[2,3-d]pyrimidine derivatives
Entry
1
3
4
5
Yield (%)a
3a
4a CH3OH
90
2
3
4
3b
3c
3a
4a
4a
93
85
86
4b CH3CH2OH
5
6
7
3b
3c
3a
4b
4b
90
85
80
4c CH3(CH2)2OH
8
9
3a
3b
3c
4d CH3(CH2)3OH
80
88
4d
4d
10
82
(Continued )

2832
N. KARIMI ET AL.
Table 1. Continued
Entry
11
3
4
5
Yield (%)a
3a
4e (CH3)2CHCH2OH
85
13
14
3a
3c
4a
89
83
4a
aYields refer to isolated pure products based on the reaction of 3(a–c) (1 mmol), salicylaldehydes 1(a–c)
(1 mmol), alcohol 4(a–e) (1.5 mmol), cat. (2 mol %), at rt and solvent-free conditions. The reaction mixture
was stirred for 40 min. All known products have been reported in the literature, and they were character-
ized by comparing their melting points and NMR spectra with authentic samples.[5]
reaction of iminochromenes and salicylaldehyde with different amines to achieve the
corresponding amino-5H-chromeno[2,3-d]pyrimidine-2-yl phenols. The reaction was
accomplished in the presence of 1 mol% of [BMIm][BF4]@[phosphonicacid@KIT-6]
as catalyst under mild reaction condition and in good yields (Scheme 4).
In conclusion, we have successfully demonstrated phosphonic acid functiona-
lized 3D cubic Ia3d KIT-6 confined [BMIm][BF4] as a green, robust, and convenient
reusable nanocatalyst for the synthesis of 4-alkoxy-5H-chromen[2,3-d]pyrimidine
derivates under solvent-free conditions. Herein, 4-alkoxy-5H-chromen[2,3-d]pyrimi-
dines was prepared via one-pot, three-component condensation of iminochromenes
and salicylaldehyde with different primary alcohols under mild conditions and in
excellent yields. Based on our observations, it could be concluded that good yields,
Table 2. Comparison of the efficiency of different catalyst in the model reaction
Entry
Catalyst
Conditionb
Yield (%)
1
2
ZnCl2
ZnCl2
Fe3O4
AlCl3
MeOH, rt
MeOH, reflux
MeOH, reflux
MeOH, reflux
MeOH, reflux
MeOH, reflux
MeOH, reflux
Neat, rt
NR
30
35
32
40
45
40
30
40
90
3
4
5
SiO2
AlCl3=SiO2
6
7
ZnCl2=SiO2
[Phosphonicacid@KIT-6]
Free catalyst
IL@[Phosphonicacid@KIT-6]a
8
9
10
[BMIm][BF4], rt
Neat, rt
aIL ¼ [BMIm][BF4].
bThe reactions run for 1 h.

IL@[PHOSPHONICACID@KIT-6]: GREEN CATALYST
2833
Scheme 3. Proposed mechanism for the synthesis of 4-alkoxy-5H-chromen[2,3-d]pyrimidines 5.
operational simplicity, practicability, and economical and environmental benefits are
the worthy advantages of this protocol.
EXPERIMENTAL
Preparation of the Catalyst, IL@[Phosphonicacid@KIT-6]
The amine functionalized mesoporous silica KIT-6 ([n-PrNH2-KIT-6]) was
prepared according to the procedure reported in our previous article.[18] Then,
as-synthesized [n-PrNH2-KIT-6] (0.2 mol amine group), crystalline phosphorous
acid (0.4 mol), and concentrated HCl (0.6 mol) were dissolved in 200 mL water,
and the mixture was refluxed in a three-necked flask fitted with thermometer, con-
denser, and dropping funnel. During 1 h, 60 mL of a 40% (w=v) aqueous formalde-
hyde solution was added dropwise, and the reaction was refluxed for 1 h. The solvent
was evaporated, and the concentrated residue was neutralized with concentrated
ammonia solution. Finally, the obtained solid was filtered off, washed with hot
dry MeOH for 12 h in a continuous extraction apparatus (Soxhelet), and then dried
at 100 ꢀC overnight to furnish the corresponding surface-bound phosphonic acid
[phosphonicacid@KIT-6]. In the next step to achieve IL@[KIT-6-phosphonicacid],
Figure 2. Recovery test of nanocatalyst for synthesis of 5a.

2834
N. KARIMI ET AL.
Scheme 4. Synthesis of amino-5H-chromeno[2,3-d]pyrimidine-2-yl phenols.
1 g of [phosphonicacid@KIT-6] was added to a solution of 1-butyl-3-methylimidazo-
lium tetrafluoroborate (3 mL) in dry acetone (50 mL). The reaction mixture was stir-
red at room temperature overnight. After stirring, acetone was removed under
reduced pressure. The resulting solid was then dried at 70 ꢀC under vacuum for
24 h, to obtain the designed catalyst IL@[KIT-6-phosphonicacid].
General Procedure for the Synthesis of 4-Methoxy-5H-
chromen[2,3-d]pyrimidine
IL@[Phosphonicacid@KIT-6] catalyst (2 mol%) was added gently to
a magnetically stirred mixture of iminocoumarine 3(a–c) (1 mmol), salicylaldehyde
1a (1 mmol), and alcohol 4(a–e) (1.5 mmol). The reaction mixture was stirred for
40 min at room temperature. The progress of the reaction was monitored by
thin-layer chromatography (TLC). When the spot for the product (Rf ꢁ 0.8 in silica
gel, EtOAc=n-hexane (1:5) was visible, the catalyst was separated by filtration or
centrifuging, and the final product was purified by column chromatography using
EtOAc=n-hexane 1:6 as an eluent and recrystallized from EtOH.
2-(4-Methoxy-5H-chromeno[2,3-d]pyrimidin-2-yl)phenol (5a)[4]
Colorless crystals; mp 198–200 ꢀC (lit. mp 200 ꢀC); 1H NMR (CDCl3,
500 MHz): dH ¼ 3.97 (s, 2H, CH2), 4.18 (s, 3H, OCH3), 6.97 (dt, J ¼ 7.5, 1.0 Hz,
1H), 7.04 (dd, J ¼ 8.0 Hz, 1H), 7.15 (dt, J ¼ 7.5 Hz, 1.0 Hz, 1H), 7.19 (d, J ¼ 7.5 Hz,
1H), 7.23–7.29 (m, 2H), 7.41 (dt, J ¼ 8.0, 1.6 Hz, 1H), 8.46 (dd, J ¼ 8.0, 1.6 Hz, 1H),
12.78 (br s, 1H, OH); 13C NMR (CDCl3, 125 MHz): dC ¼ 21.30, 54.22, 94.41, 116.84,
117.31, 117.86, 118.43, 124.16, 127.76, 128.70, 128.75, 132.62, 136.81, 149.88, 159.78,
161.70, 167.14. Anal. calcd. for C18H14N2O3: C, 70.58; H, 4.61; N, 9.15. Found: C,
70.72; H, 4.90; N, 9.38.
FUNDING
This research was supported by grants from the research council of Tehran
University of Medical Sciences, INEF (Iran National Elites Foundation), and INSF
(Iran National Science Foundation).

IL@[PHOSPHONICACID@KIT-6]: GREEN CATALYST
2835
SUPPORTING INFORMATION
Full experimental details, 1H and 13C NMR spectra, and catalyst synthesis can
be accessed on the publisher’s website.
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