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Nano magnetic double-charged diazoniabicyclo[2.2.2]octane dichloride silica hybrid: Synthesis, characterization, and application as an efficient and reusable organic–inorganic hybrid silica with ionic liquid framework for one-pot synthesis of pyran annulated heterocyclic compounds in water

Nano magnetic double-charged diazoniabicyclo[2.2.2]octane dichloride silica hybrid: Synthesis, characterization, and application as an efficient and reusable organic–inorganic hybrid silica with ionic liquid framework for one-pot synthesis of pyran annulated heterocyclic compounds in water

Accepted Manuscript Title: Nano magnetic double-charged diazoniabicyclo[2.2.2]octane dichloride silica hybrid: Synthesis, characterization, and applic...

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Accepted Manuscript Title: Nano magnetic double-charged diazoniabicyclo[2.2.2]octane dichloride silica hybrid: Synthesis, characterization, and application as an efficient and reusable organic-inorganic hybrid silica with ionic liquid framework for one-pot synthesis of pyran annulated heterocyclic compounds in water Author: Jamal Davarpanah Ali Reza Kiasat Siamak Noorizadeh Mahboubeh Ghahremani PII: DOI: Reference:

S1381-1169(13)00158-1 http://dx.doi.org/doi:10.1016/j.molcata.2013.04.020 MOLCAA 8739

To appear in:

Journal of Molecular Catalysis A: Chemical

Received date: Revised date: Accepted date:

26-3-2013 9-4-2013 10-4-2013

Please cite this article as: J. Davarpanah, A.R. Kiasat, S. Noorizadeh, M. Ghahremani, Nano magnetic double-charged diazoniabicyclo[2.2.2]octane dichloride silica hybrid: Synthesis, characterization, and application as an efficient and reusable organicinorganic hybrid silica with ionic liquid framework for one-pot synthesis of pyran annulated heterocyclic compounds in water, Journal of Molecular Catalysis A: Chemical (2013), http://dx.doi.org/10.1016/j.molcata.2013.04.020 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Nano magnetic double-charged diazoniabicyclo[2.2.2]octane dichloride silica hybrid:

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Synthesis, characterization, and application as an efficient and reusable organic-inorganic hybrid silica with ionic liquid framework for one-pot synthesis of pyran annulated

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cr

heterocyclic compounds in water

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Jamal Davarpanah, Ali Reza Kiasat*, Siamak Noorizadeh, Mahboubeh Ghahremani

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Chemistry Department, College of Science, Shahid Chamran University, Ahvaz 61357-43169, Iran

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Tel/Fax: (+98) 611-3331746, Email: [email protected]

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Abstract Organosilane containing bridged double-charged diazoniabicyclo[2.2.2] octane dichloride groups, [(MeO)3Si(CH2)3N+(CH2CH2)3N+(CH2)3 Si(OME)3]Cl2, was easily prepared and used as

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a precursor reagent to obtain core-shell composite using Fe3O4 spheres and the positively doublecharged organic-inorganic hybrid silica as the core and shell, respectively. For this reason, the

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surface of synthesized magnetite nanoparticles by the co-precipitation of FeCl2 and FeCl3, was

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successfully engineered by deposition of organic-inorganic hybrid silica with ionic liquid framework onto nano particles surface using the ammonia-catalyzed hydrolysis of alkoxysilanes

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groups of organosilane precursor and tetraethylorthosilicate. The magnetic double-charged diazoniabicyclo[2.2.2]octane chloride silica hybrid, [email protected]/DABCO, was characterized by

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infrared spectroscopy (FT-IR), X-ray diffraction (XRD) spectroscopy, scanning electron

d

microscope (SEM), vibrating sample magnetometer (VSM), thermogravimetric analysis (TGA)

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and differential thermal analysis (DTA). The catalytic activity of the magnetic catalyst was probed through one-pot synthesis of pyran annulated heterocyclic compounds via three-

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component couplings of aromatic aldehydes, malononitrile and -diketone (4-hydroxycoumarin, dimedone

and

4-hydroxy-6-methyl-2-pyrone)

in

water.

Due

to

water-resistant

and

superparamagnetic nano-nature of [email protected]/DABCO, it could be easily separated by-passing time consuming filtration operation by using an external magnet device and then reused it conveniently. In addition to the facility of this methodology, it also enhances product purity and promises economic as well as environmental benefits. Furthermore, the NMR spectrum of the 2amino-3-cyano-4-phenyl-8-methylpyrano[3,2-c]pyran-5(4H)-one compound is simulated at HF/6-311++G** level of theory. It is shown that the calculated 1H and 13C chemical shifts are in well agreement with the obtained experimental ones.

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Keywords: Organic-inorganic hybrid silica; Magnetite core-shell composite; Double-charged hybrid silica; Pyran annulated heterocyclic compounds; Theoretical NMR simulation.

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1. Introduction

Hybrid xerogel materials, where the organic component is bonded to a polymeric silica skeleton

cr

framework, have attracted significant attention over the last decade. In this context, single and

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double charged silica-based hybrid xerogels containing the 1-azonia-4-azabicyclo[2.2.2]octane, DABCO, chloride group have recently drawn particular interest [1,2]. The potential applications

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of these charged silica-based hybrid materials as metal adsorbents from aqueous solutions, stationary phase for chromatography [3,4] and for immobilization of electroactive species that

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allow preparing chemically modified electrodes have been proposed [5]. Thin film of silica-

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based hybrid xerogel containing the double charged group diazoniabicyclo[2.2.2]octane chloride

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was also fabricated and its optical properties were previously investigated [6]. Although, the application of charged DABCO grafted onto silica-gel surfaces as a

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catalyst in organic transformation was previously discussed [7], the application of xerogels containing double charged groups bonded to the silica framework has not been reported yet. Of interest has been to prepare core-shell nanocomposite using Fe3O4 spheres as the core and the positively double-charged organic-inorganic hybrid silica as the shell. The nanomagnetic catalyst could be readily separated from solution via application of an external magnet, allowing straightforward recovery and reuse. In other hand, science and technology are shifting emphasis on economically and environmentally benign and sustainable processes. In that regards, development of one-pot multicomponent coupling reaction (MCR) strategies in aqueous medium has been of

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considerable interest and is a powerful synthetic tool for the synthesis of biologically active compounds. The usefulness of MCRs is strengthened as they generally afford good yields and provide rapid access to various heterocyclic scaffolds for diverse applications [8].

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Pyran annulated coumarins have wide range of biological properties and are widely distributed in nature [9]. Aminochromene derivatives exhibit a wide spectrum of biological

cr

activities including anticancer, antimicrobial agents, photoactive materials, and also utilized in

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synthesis of blood anticoagulant warfarin and tacrine analogs [7,8,10-15]. Consequently, several methods have been reported for the promoting preparation of pyran annulated heterocyclic

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compounds. However, most of these methods suffer from some drawbacks such as low yields, extended reaction times, harsh reaction conditions, tedious work-up procedures, toxic solvents

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and application of expensive or unavailability catalysts. Moreover, in most of the reported

d

methods, catalysts are not recyclable. Therefore, to overcome these drawbacks a great deal of

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efforts is directed to develop an efficient catalytic system for synthesis of these compounds. In the present study, we present our results on the preparation and characterization of magnetic

double-charged

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novel

diazoniabicyclo[2.2.2]octane

chloride

silica

hybrid,

[email protected]/DABCO, and its catalytic application for one-pot multicomponent synthesis of pyran annulated heterocyclic compounds in water. Also some theoretical spectroscopic investigations are also performed on one of these compounds. 2. Experimental 2. 1. General Iron (II) chloride tetrahydrate (99%), iron (III) chloride hexahydrate (98%), aromatic aldehydes and other chemical materials were purchased from Fluka and Merck companies and used without further purification. Products were characterized by comparison of their physical data, such as IR

4 Page 4 of 31

and 1H NMR and 13C NMR spectra, with known samples. NMR spectra were recorded in CDCl3 on a Bruker Advance DPX 400 MHz instrument spectrometer using TMS as internal standard. IR spectra were recorded on a BOMEM MB-Series 1998 FT-IR spectrometer.

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The purity determination of the products and reaction monitoring were accomplished by TLC on silica gel PolyGram SILG/UV 254 plates. The TGA curve of the [email protected]/DABCO

cr

was recorded on a BAHR, SPA 503 at heating rates of 10 °C min-1. The thermal behavior was

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studied by heating 1-3 mg of samples in aluminum-crimped pans under N2 atmosphere, over the temperature range of 25-1000 °C. The particle size and external morphology of the particles were

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characterized by scanning electron microscopy, SEM (Philips XL30 scanning electron microscope). X-ray diffraction (XRD) patterns of samples were taken on a Philips X-ray

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diffractometer Model PW 1840.

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2. 2. Preparation of Fe3O4 superparamagnetic nanoparticles

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Superparamagnetic nanoparticles (MNPs) were prepared via improved chemical coprecipitation method [16]. According to this method, FeCl2.4H2O (6.346 g, 31.905 mmol) and FeCl3.6H2O

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(15.136 g, 55.987 mmol) were dissolved in 640 mL of deionized water. The mixed solution was stirred under N2 at 90 °C for 1 h. 80 mL of NH3.H2O (25%) was injected into the reaction mixture rapidly, stirred under N2 for another 1h and then cooled to room temperature. The precipitated particles were washed five times with hot water and separated by magnetic decantation. Finally, magnetic NPs were dried under vacuum at 70 °C. 2. 3. Synthesis of bis(n-propyltrimethoxysilane)-1,4-diazoniabicycle [2.2.2]octane chloride, BPTDABCOCl: BPTDABCOCl was prepared according to the procedure described by Arenas et al [3]. Initially, the previously sublimed DABCO (0.897 g, 8.0 mmol) was dissolved in DMF (5 ml). To this

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solution 16 mmol of 3-chloropropyltrimethoxysilane, CPTMS, was added. The mixture was stirred for 72 h, under argon atmosphere at 90 °C. The white solid, BPTDABCOCl, was filtered and washed with methanol and then dried for 2 h in an oven at 90 °C.

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2. 4. Preparation of Magnetic double-charged diazoniabicyclo[2.2.2]octane dichloride silica hybrid, [email protected]/DABCO:

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[email protected]/DABCO was prepared by sol-gel process. 2.0 g of the synthesized magnetite

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nanoparticles was first diluted with water (40 ml), absolute ethanol (120 ml) and 3.0 mL ammonia aqueous (25 %). This suspension was well-dispersed by ultrasonic vibration for 15

an

min. To this dispersed suspension, BPTDABCOCl (5 g), previously dissolved in DMF (7 mL), was added. Then under continuous mechanical stirring, 1.5 ml of TEOS diluted in ethanol (40

M

ml) was slowly added to this dispersion, and after stirring for 48 h, the obtained magnetic

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with ethanol.

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nanocomposite, [email protected]/DABCO silica was collected by magnetic separation and washed

2. 5. Typical procedure for the one-pot preparation of pyran annulated heterocyclic compounds:

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A mixture of -diketone (dimedone, 4-hydroxycoumarin or 4-hydroxy-6-methyl-2-pyrone) (1 mmol), malononitrile (1 mmol), aldehyde (1 mmol) and [email protected]/DABCO (0.05 g) was heated at 80 °C min in water for the time shown in Table 1. After complete consumption of aromatic aldehyde as judged by TLC (using n-hexane-ethylacetate as eluent), the reaction was allowed to cool to room temperature and the magnetic catalyst was concentrated on the sidewall of the reaction vessel using an external magnet. The solid residue was isolated and purified by recrystallization in hot EtOH. The desired pure product(s) was characterized by comparison of their physical data with those of known 4H-benzo[b]pyrans. 3. Results and Discussions

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3.

1.

Investigation

around

the

approach

of

magnetic

double-charged

diazoniabicyclo[2.2.2]octane chloride silica hybrid, [email protected]/DABCO preparation and its structural and morphological analysis

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Magnetic nano catalysts have the advantages of both magnetic separation techniques and nanosized materials, which can be easily recovered or manipulated with an external magnetic field.

cr

As the catalysts are usually immobilized on the surface of the magnetic nanoparticles, easy

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access of reactants to the active sites of the nano-complex, can also be achieved. In present study organosilane containing bridged double-charged diazoniabicyclo[2.2.2] octane dichloride groups,

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[(MeO)3Si(CH2)3N+(CH2CH2)3N+(CH2)3 Si(OME)3]Cl2, was easily prepared and used as a precursor reagent to obtain core-shell composite using Fe3O4 spheres as the core and the

M

positively double-charged organic-inorganic hybrid silica as the shell. For this reason, the surface

d

of the synthesized magnetite nanoparticles was successfully engineered by deposition of organic-

te

inorganic hybrid silica with ionic liquid framework and the ammonia-catalyzed hydrolysis of alkoxysilanes groups of organosilane precursor and tetraethylorthosilicate. The systematic steps

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of [email protected]/DABCO preparation was shown in Scheme 1.

7 Page 7 of 31

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Scheme 1. Synthesis of [email protected]/DABCO

The coating of Fe3O4 by double-charged organic-inorganic hybrid silica was verified by FT-IR studies. Fig. 1 shows the FT-IR spectra of Fe3O4, [email protected]/DABCO and BPTDABCOCl

in

the

400-4000

cm-1.

The

FT-IR

analysis

of

the

Fe3O4

and

[email protected]/DABCO exhibit basic characteristic peak at approximately 580 cm-1, which was attributed

to

the

presence

of

Fe-O

stretching

vibration.

In

BPTDABCOCl

and

[email protected]/DABCO spectra, the presence of peaks at 440, 780 and 990-1200 cm-1 were most 8 Page 8 of 31

probably due to the symmetric and asymmetric stretching vibrations of framework and terminal Si-O groups. The C-H stretching peaks at 1200-1500 and 2870-3040 cm-1 in the [email protected]/DABCO spectra indicate that the magnetic particles are successfully coated by

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double-charged diazoniabicyclo[2.2.2]octane chloride silica hybrid. BPTDABCOCl and [email protected]/DABCO showed a band at 1465 cm-1 which is characteristic for the tertiary amine

cr

group. In BPTDABCOCl, the band around 1635 cm-1 is also due to the bending vibration of

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d

M

an

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water molecules which were adsorbed on the surface.

Fig. 1. The FT-IR spectra of Fe3O4, [email protected]/DABCO and BPTDABCOCl

The presence as well as the degree of crystallinity of magnetic iron oxide (Fe3O4) in the synthesized [email protected]/DABCO was obtained from XRD measurements (Fig. 2). According to the database of Joint Committee on Powder Diffraction Standards (JCPDS)(JCPDs:19-629), the XRD pattern of a standard Fe3O4 crystal with spinel structure has six characteristic peaks at 2Ө = 30.5°, 35.8°, 43.4°, 53.8°, 57.5°, and 63.1° [18]. The pattern of [email protected]/DABCO displays a most intense at 2Ө= 35.83. This line, which is corresponded to the pure Fe3O4 [21], confirms the 9 Page 9 of 31

presence of Fe3O4. It is also apparent that the analysis results of the Fe3O4 and [email protected]/DABCO fitted to the pattern exhibited by standard magnetite. Therefore, it can be concluded that the obtained [email protected]/DABCO show spinel structure and these modifications

M

an

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cr

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don’t cause a phase change in Fe3O4 [17].

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Fig. 2. XRD pattern of (a) Fe3O4 and (b) [email protected]/DABCO

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Scanning electron microscopy (SEM) has been a primary tool for determining the size distribution, particle shape, surface morphology and fundamental physical properties. Fig. 3

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depicts the SEM images of Fe3O4 and [email protected]/DABCO microspheres. The size of the Fe3O4 and [email protected]/DABCO microspheres are around 48 and 74 nm, respectively, which indicate that the organic-inorganic hybrid silica is successfully anchoring to the magnetic particles.

10 Page 10 of 31

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Fig. 3. The SEM images of (a) Fe3O4 and (b) [email protected]/DABCO microspheres

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It should be mentioned that the core-shell material possess sufficient magnetic and

M

superparamagnetic properties for practical applications. The magnetic properties of the uncoated magnetic iron oxide (Fe3O4) and positively double-charged organic-inorganic hybrid silica

d

coated Fe3O4 nanoparticles, [email protected]/DABCO, were measured by vibrating sample

of

superparamagnetic

behavior MNPs.

can

The

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[email protected]/DABCO

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magnetometer, VSM, at room temperature. In Fig. 4, the hysteresis loops that are characteristic be

clearly

magnetic

observed

saturation

for

values

of

both

Fe3O4

and

the

Fe3O4

and

[email protected]/DABCO nanoparticles are 68 and 49 emu g-1 at r.t., respectively. Lower magnetic saturation of later nanoparticles could be due to the existence of nonmagnetic materials (positively double-charged organic-inorganic hybrid silica) on the surface of nanoparticles. Both particles shown high permeability in magnetization and their magnetization is sufficient for magnetic separation with a conventional magnet. The reversibility in hysteresis loop confirms that no aggregation imposes to the nanoparticles in the magnetic fields.

11 Page 11 of 31

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Fig. 4. VSM magnetization curves of the (a) Fe3O4, (b) [email protected]/DABCO nanoparticles

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The thermal stability of nanocomposite was also investigated by TGA and DTA. The TGA thermogram of [email protected]/DABCO in N2 atmosphere is shown in Fig 5-a. The 3%

d

weight loss below 200 °C might be due to the loss of the adsorbed water as well as dehydration

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of the surface –OH groups. The differential thermal analysis (DTA) is shown in Fig. 5-b and no

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transition was observed up to 600 °C. A sharp endotherm transition in around 600 °C was due to the breakdown and decomposition of organic moieties. Thus, the TGA and DTA curves also convey the obvious information that the magnetic particles are successfully coated by doublecharged diazoniabicyclo[2.2.2]octane chloride silica hybrid.

12 Page 12 of 31

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Fig. 5. (a) TGA and (b) DTA Curves of [email protected]/DABCO

3. 2. Application of [email protected]/DABCO as nanomagnetic catalyst for one-pot synthesis of 4Hbenzo[b]pyran derivatives

In the presence of acid or base 4-hydroxycoumarin (pKa 0.735 at 70 oC in water), dimedone and 4-hydroxy-6-methyl-2-pyrone are in the enol tautomers of the corresponding 1,3-dicarbonyl compounds. Therefore they can act as nucleophiles to form 4H-benzo[b]pyran derivatives [19].

13 Page 13 of 31

We achieved the synthesis of 4H-benzo[b]pyran derivatives using [email protected]/DABCO as

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d

M

an

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cr

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catalyst (Scheme 2).

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Scheme 2. Synthesis of 4H-benzo[b]pyran derivatives through multicomponent reaction promoted by [email protected]/DABCO

To investigate the catalytic activity of [email protected]/DABCO in the one-pot multicomponent synthesis of pyran annulated heterocyclic compounds, we focused on systematic evaluation of different conditions for the model three-component couplings of benzaldehyde, malononitrile and dimedone. Various solvents and temperature, were screened to test the efficiency of the catalyst and the results are summarized in Table 1. Excellent yield of coupling product were obtained under the optimized conditions using 0.05 g of catalyst in water as solvent at 80 oC in 25 min (Scheme 3). It should be pointed out that in the absence of [email protected]/DABCO, the

14 Page 14 of 31

reaction was sluggish and even after prolonged reaction time a considerable amount of starting material was remained. O

NH2

CHO + O

C C

0.05 gr catalyst

+

C

O

N

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N

H2O, 80 oC, 25 min

N

O

cr

90 %

(1 mmol) in water

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Scheme 3. The one-pot three component reaction of benzaldehyde (1mmol), malononitrile (1 mmol) and dimedone

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For assessing the generality of optimized reaction condition, a wide range of substituted aldehydes were allowed to undergo this three-component condensation. Both of the aromatic

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aldehydes with electron-withdrawing and electron-donating functionalities (Table 2) were found to be compatible under the optimized reaction condition. The structures of products were

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d

determined from their analytical and spectral (IR, 1H & 13C NMR) data and by direct comparison with authentic samples. Formation of the products were also confirmed with the comparison of

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their melting points with the products prepared by reported methods [7,9,20-22]. Table 1. The one-pot three component reaction of benzaldehyde (1mmol), malononitrile (1 mmol) and dimedone (1 mmol) under different conditions

Entry

Solvent

T oC

Catalytic

Yield

amount (g)

(%)

1

CH2Cl2

r.t

0.05

40

2

Toluene

r.t

0.05

45

3

CH3CN

r.t

0.05

45

4

EtOH

r.t

0.05

65

15 Page 15 of 31

r.t

0.05

70

6

H2O

Reflux

0.05

Mixa

7

H2O

60

0.05

84

8

H2O

80

0.05

90

9

H2O

80

0.025

10

H2O

80

1

11

Solvent free

100

0.05

12

Solvent free

60

60

cr

90

Mix

us

: Mixture of products

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H2O

0.05

40

an

a

5

To probe the efficiency and scope of the present protocol, we also examined 4-

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hydroxycoumarin and 4-hydroxy-6-methyl-2-pyrone as enol tautomers in the reaction with malononitrile and different aldehydes, and the products (Table 2, entry 12-31) were obtained in

d

excellent yields (Scheme 2). The results are summarized in Table 2.

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Table 2. Synthesis of 4H-benzo[b]pyran derivatives through multicomponent reaction in presence of

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[email protected]/DABCO

Entry

1,3 dicarbonyl

O

1

Aldehyde

Product

NH2 C

O

CHO

NH2 C

O

2

O

Yield

(min)

(%)

25

90

40

86

N

O

O

Time

N

Me

16 Page 16 of 31

O

CHO

O Me

NH2

O

O

OMe

NH2

O

O

CHO

M

Cl

84

25

90

30

90

30

89

25

89

N

an

4

O

C

O

CHO

45

us

OMe

O

ip t

3

cr

CHO

O

N

C

O

NH2 C

O

Cl

N NO2

d

NO2

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O

O

6

NH2

O

O

N Me

O

Me

NH2 C

O

CHO

7

C

O

CHO

O

O

te

5

N F

O

F

17 Page 17 of 31

NH2

8

N

O

O

NO2 NH2 O

CHO

Cl

O

Cl

O

NH2

10

M

d

Cl

CHO

89

30

89

35

89

35

88

35

87

Cl

O

O

30

N

an

Cl

O

C

O

CHO

O

N

cr

9

C

92

us

O

25

NO2

ip t

O

CHO

O

C

NH2 C

O

Cl

N Cl

11

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O

OH

12

O

O

O

NH2 C

O

CHO

N NO2

NO2

O

O

OH

13

te

Cl

O NH2 C

O

CHO

O

O

O

N

18 Page 18 of 31

NH2 OH

14

O

C

O

CHO

O

O

N

O

O

O

O

NH2

C

M

O

O

O

NO2

45

80

35

90

40

88

40

86

35

85

OMe

an

O

CHO

OH

N

cr

O

OMe

16

C

us

15

NH2

CHO

83

ip t

Me

OH

45

Me

O

NO2

te

d

O

N

Ac ce p

17

O

O

O

O

Cl

O

N

O

O

NH2 C

O

CHO

OH

19

C

O

OH

18

NH2

CHO

OH

Cl N Cl

O

Cl

O

CHO

O

F

19 Page 19 of 31

NH2

N

C

O

F

OH

NH2

CHO

O

Me

Me

O

NH2

an

CHO Cl

O

O

Cl

O

d

OH

CHO

84

45

84

40

87

40

84

35

87

N

C

O

M

21

O

40

us

O

OH

N

C

O

cr

20

O

ip t

O

Cl

O

Cl

NH2 C

O

N Cl

O

O

Ac ce p

22

OH

23

O

O

O

O

NH2 C

O

CHO

O

O

N

O

Me

Me

NH2 C

O

CHO

OH

24

te

Cl

O

O

O

N

Cl

Cl

20 Page 20 of 31

NH2 O

OH

25

O

NO2

O

N

C

O

O

NO2

NH2

26

O

CHO

O

Cl O

Cl

cr

OH

N

C

O

O

OH

O

CHO

O

Ac ce p

OH

29

O

O

an O

NH2

C

O

O

86

35

85

45

80

35

87

40

88

N

O

C

O

CHO

O

N

O

OMe

OMe

NH2 C

O

CHO

O

O

C

O

CHO

N

O NH2

OH

40

F

NH2

O

OH

30

F

te

28

O

Me

O

M

O

86

Me

d

27

40

N

C

O

CHO

90

us

NH2 OH

25

ip t

CHO

N Cl

Cl

31

O

O

O

O

21 Page 21 of 31

To investigate the activity constancy of the catalyst, the catalyst was reused six times in the one-pot multicomponent condensation of benzaldehyde, malononitrile and dimedone in water. The catalyst was magnetically recovered after each run, washed with water and ethanol, dried in

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an oven at 80 °C for 30 min prior to use and tested for its activity in the subsequent run (Fig. 6).

Ac ce p

te

d

M

an

us

cr

As shown in Fig. 6, smooth loss of catalytic activity of [email protected]/DABCO was observed.

Fig. 6. Recyclability of [email protected]/DABCO

3.3. Theoretical section

In this section it is attempted to simulate 1H and 13C NMR chemical shifts of the title compound and compared the obtained values with experimental results. For this purpose the product of reaction between 4-hydroxycoumarin, malononitrile and benzaldehydes (entry 13 in Table 2) was selected to assign each peak to the corresponding atom. The geometry of the corresponding product (entry 13 in Table 2) was fully optimized at B3LYP/6-311++G(d,p) level of theory. The obtained optimized structure which its minimum nature was checked by frequency analysis at the same computational level, is depicted in Fig. 7. Since the experimental chemical shifts are 22 Page 22 of 31

obtained in DMSO solvent, the chemical shieldings of titled compound as well as tetramethylsilane (TMS) were calculated under the GIAO formalism [23] and HF/6-311++G(d,p) method in DMSO solvent using IEFPCM model. All calculations were performed using

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Gaussian03 program revision A.02 [24]. The 1H and 13C NMR chemical shifts were scaled to the

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TMS with the values of 32.1594 (1H) and 195.0972 (13C) ppm in DMSO solvent, respectively.

Fig. 7. The optimized geometry (entry 13 in Table 2)

Both of the experimental and theoretical 1H and

13

C NMR spectra for the considered

compound are given in Fig. 8 and the calculated chemical shifts are also summarized in Table 3. It is obvious from this table that all of the calculated 1H/13C chemical shifts with respect to TMS are in the range of 2.22-7.95/21.63-180.08 ppm; whereas the experimental values are observed at 2.22-7.31/19.75-163.33 ppm. It is noteworthy that the positions of the hydrogen atoms of NH2 group (27-H and 28-H in Fig. 7) are very sensitive to different conditions and are changed by different experiments. Therefore these peaks are excluded and the correlations between the 23 Page 23 of 31

experimental and computed 1H and

13

C chemical shifts are depicted in Fig. 9. It is clear that

although significant correlations are observed between the experimental and calculated spectra, the correlation for 13C chemical shifts (R2 =0.996) is to some extent better than those of protons

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(R2 =0.991). Note that the evaluated slopes for both graphs are close to unity (0.893 and 0.900 for 1H and 13C spectra, respectively) which indicates the similarity between the experimental and

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the corresponding calculated spectra.

H NMR and 13C NMR for the entry 13 in Table 2. (All in ppm)

3-C

180.08

163.39

10-C

173.79

161.82

5-C

173.60

158.64

1-C

172.14

158.53

15-C

153.21

16-C

Atom

 Calc .

 Exp .

29-H

7.95

7.31

32-H

7.78

7.31

30-H

7.74

7.31

31-H

7.67

7.21

33-H

7.62

7.21

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 Exp .

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 Calc .

te

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Atom

144.08

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Table 3. The calculated (  Calc . ) and experimental (  Exp . ) chemical shift values of

138.85

128.89

22-H

6.02

6.28

137.57

127.96

26-H

4.02

4.27

137.09

127.45

25-H

2.38

2.50

135.93

127.45

24-H

2.30

2.38

135.66

127.45

23-H

2.22

2.22

12-C

128.52

119.81

6-C

102.79

101.18

2-C

98.78

98.40

9-C

63.52

58.31

19-C 20-C 17-C 18-C

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33.56

36.72

7-C

21.63

19.76

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8-C

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26

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Fig. 8. The obtained experimental (a) 1H NMR and (b) theoretical (c) 1H NMR and (d)

13

13

C NMR spectra together with

C NMR spectra simulated at HF/6-311++G** in DMSO for

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the entry 13 in Table 2. (see Fig. 7)

chemical shifts of the entry 13 in Table 2.

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Fig. 9. The correlations between the experimental and calculated (a) 13C NMR together with (b) 1H NMR

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4. Conclusion

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In this work, magnetic double-charged diazoniabicyclo[2.2.2]octane dichloride silica hybrid

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([email protected]/DABCO) was successfully synthesized as a novel catalyst and characterized by FT-IR, XRD, SEM, VSM, DTA and TGA. The catalytic activity of this magnetic hybrid as solid-liquid catalyst for the synthesis of pyran annulated heterocyclic compounds in water was investigated. In these reactions, [email protected]/DABCO shows a highly catalytic nature, easy to handle procedure, short reaction time, recycle exploitation and excellent isolated yields. The nanomagnetic catalyst could also be readily separated from solution via application of an external magnet, allowing straightforward recovery and reuse. Moreover the NMR spectrum of the 2-amino-3-cyano-4-phenyl-8-methylpyrano[3,2-c]pyran-5(4H)-one compound is simulated at HF/6-311++G** level of theory. It is shown that the calculated 1H and 13C chemical shifts are in well agreement with the obtained experimental ones. 27 Page 27 of 31

Acknowledgments We are grateful to financial support from the Research Council of Shahid Chamran University.

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[6] M.B. Pereira, A.F. Michels, D.S.F. Gay, E.V. Benvenutti, T.M.H. Costa, F. Horowitz, Opt. Mater. 32 (2010) 1170-1176.

[7] A. Hasaninejad, M. Shekouhy, N. Golzar, A. Zare, M.M. Doroodmand, Appl. Catal., A: Gen. 402 (2011) 11-22.

[8] Z. Chen, Q. Zhu, W. Su, Tetrahedron Lett. 52 (2011) 2601-2604. [9] A.T. Khan, M. Lal, S. Ali, M.M. Khan, Tetrahedron Lett. 52 (2011) 5327-5332. [10] J.M. Khurana, B. Nand, P. Saluja, Tetrahedron 66 (2010) 5637-5641. [11] J.M. Khurana, S. Kumar, Tetrahedron Lett. 50 (2009) 4125-4127. [12] M.M. Heravi, S. Sadjadi, N.M. Haj, H.A. Oskooie, F.F. Bamoharram, Catal. Commun. 10 (2009) 1643-1646. 28 Page 28 of 31

[13] S. Abdolmohammadi, S. Balalaie, Tetrahedron Lett. 48 (2007) 3299-3303. [14] H. Mehrabi, H. Abusaidi, J. Iran. Chem. Soc, 7 (2010) 890-894. [15] B. Karami, S. Khodabakhshi, K. Eskandari, Tetrahedron Lett. 53 (2012) 1445-1446.

[17] A.R. Kiasat, S. Nazari, J. Mol. Catal. A: Chem. 365 (2012) 80-86.

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[16] K.D. Kim, S.S. Kim, Y.H. Choa, H.T. Kim, J. Ind. Eng. Chem. 13 (2007) 1137-1141.

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[19] S. Paul, P. Bhattacharyya, A.R. Das, Tetrahedron Lett. 52 (2011) 4636-4641. [20] H.R. Shaterian, A.R. Oveisi, J. Iran. Chem. Soc. 8 (2011) 545-552.

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[21] E.V. Stoyanov, I.C. Ivanov, D. Heber, Molecules 5 (2000) 19-32.

[22] X. Fan, D. Feng, Y. Qua, X. Zhang, J. Wang, P.M. Loiseau, G. Andrei, R. Snoeck, E.

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DeClercq, Bioorg. Med. Chem. Lett. 20 (2010) 809-813.

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[23] R. Ditchfield, Mol. Phys. 27 (1974) 789-807.

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[24] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,V.G. Zakrzewski, J.A. Montgomery, Jr. R.E. Stratmann, J.C. Burant, S. Dapprich, J.M. Millam, A.D.

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Daniels, K.N. Kudin, M.C. Strain, O. Farkas, J. Tomasi, V. Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clifford, J. Ochterski, G.A. Petersson, P.Y. Ayala, Q. Cui, K. Morokuma, D.K. Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman, J. Cioslowski, J.V. Ortiz, A.G. Baboul, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, C.Gonzalez, M. Challacombe, P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, J.L. Andres, C. Gonzalez, M. Head-Gordon, E.S. Replogle, J.A. Pople, Gaussian 03 Inc., revision A.02, Pittsburgh.

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Graphical a bstract

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Highlights Reusable nanomagnetic catalyst One-pot synthesis of pyran annulated heterocyclic compounds

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Bridged double-charged diazoniabicyclo[2.2.2] octane dichloride Hybrid xerogel materials

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One-pot multicomponent coupling reaction in water

31 Page 31 of 31