An expedient synthesis of oxazolones using a cellulose supported ionic liquid phase catalyst

Rajanikant Kurane, Sharanabasappa Khanapure, Dolly Kale, Rajashri Salunkhe and Gajanan Rashinkar*
Department of Chemistry, Shivaji University, Kolhapur, 416004, M.S., India. E-mail: gsr_chem@unishivaji.ac.in; Fax: +91 231 2692333; Tel: +91 231 260 9169

Received 11th February 2016 , Accepted 24th April 2016

First published on 26th April 2016


A novel cellulose supported ionic liquid phase catalyst containing hydroxide ions ([CellFemImi]OH) has been synthesized by covalent anchoring of 1-N-ferrocenylmethyl imidazole in the functionalized cellulose matrix followed by an anion metathesis reaction. The [CellFemImi]OH was characterized by various techniques including FT-IR, FT-Raman, 13C solid state NMR, X-ray diffraction, energy dispersive X-ray (EDX) analysis, field emission scanning electron microscopy (FESEM) and thermogravimetric analysis. The [CellFemImi]OH was effectively employed as a heterogeneous catalyst in the synthesis of oxazolones by cyclocondensation of aryl aldehydes with hippuric acid in the presence of acetic anhydride.


Introduction

Green chemistry necessitates a paradigm shift from traditional chemical processes to more sustainable catalytic processes.1 Tremendous strides have been made to achieve the goal of greater sustainability through applications of green chemistry principles. The concept of supported ionic liquid phase (SILP) catalysis involving immobilization of ionic liquids (ILs) onto a surface of a porous high area support material constitute one of the most promising tools in the chemist's tool box for realizing sustainable chemical processes.2 This new class of advanced materials dramatically reduces the amount of ILs used, retaining their properties. There are potentially multiple advantages employing SILP catalysts in organic synthesis. These include ease of separation of products as well as catalyst recycling along with significant advances in activity and selectivity. In addition, the processes applying SILP catalysts can be performed in continuous mode using fix bed reactors.3 The SILP catalysts are usually prepared by depositing ILs on the surface of high area porous material either by covalent bonding or van der Waals interactions.4 The majority of the supports used in SILP catalysis are either porous silica gels or polymer based materials.5 In addition, carbon nanotubes,6 active carbon cloth,7 chitosan,8 magnetic nanoparticles9 and carbon nanofibers supported on sintered metal fibers10 have also been sporadically employed as supports. Over the past few years, intense research in this field has greatly expanded the scope of SILP catalyzed reactions by designing structurally diverse SILP catalyst based on various supports.11 Although tremendous progress has been already made, the field of SILP catalysis is still in its infancy and extension of this technology using SILP catalysts from bio renewable feedstock is yet to be fully exploited.

Cellulose is the most abundant and environmentally benign renewable biopolymer in the ecosphere.12 It is composed of long linear polymeric chain made up of repeating units of β-D-glucose linked by 1,4-glycosidic bonds. Cellulose has an unusual structure in which every other glucose monomer is flipped over and packed tightly as extended long chains. This imparts cellulose rigidity and high tensile strength. Owing to multiple hydrogen bonding interactions between the individual chains, cellulose is insoluble in water and most common solvents.13 A unique attribute of cellulose is its structure that can be easily modified with the help of surface hydroxyl groups. In addition to aforementioned properties, its high surface area, non-toxicity, stability in common organic solvents, unlimited availability as a renewable agro-resource, limited carbon footprint and excellent biodegradability makes cellulose the most potential feedstock for producing materials for catalytic applications.14 The tempting properties of cellulose spurred us to investigate its compatibility in the synthesis of SILP catalysts.

Oxazolones are privileged scaffolds that are compatible in the synthesis of natural or artificial bioactive molecules on account that they may serve as protected amino acids.15 They also act as carbon centered nucleophiles in enantioselective organocatalysis.16 They are main intermediates in the synthesis of various fine chemicals, amino acids, carboxylic acids, peptides, herbicides, fungicides, skin sensitizers and photosensitizers.17 Their derivatives exhibits important properties such as antimicrobial, antifungal and anticancer activities.18a,b Oxazolone grafted MNPs are used as efficient drug delivery agents, particularly for cancer treatment18c and act as anti-inflammatory,18d antiallergic18e and efficient cell permeable agents.18f In addition, they serve as anticonvulsants,18g antiangeogenetics18h and antioxidants.18i The unique structural properties as well as their biological and pharmaceutical relevance have motivated research aimed at the development of efficient strategies to access these compounds. Oxazolones are synthesized under mild conditions by the reaction of N-acylated amino acid derivatives with dehydrating reagents which usually consist of activated anhydrides or carbodiimides.19 Although there are several methods for the synthesis of oxazolones, the classical and most widely used strategy includes Erlenmeyer reaction which involves cyclodehydration of hippuric acid followed by condensation with an aldehyde in the presence of acetic anhydride.20 Several catalysts such as, [Et3NH][HSO4],21a TsCl/DMF under microwave,21b POCl3,21c CuSO4·5H2O/[(Ph3P) (NCMe)]SbF6,21d alum,21e Yb(OTf)3,21f Bi(OAc)3,21g Fe2O3-nanoparticles,21h ferrocene bis-imidazoline bis-palladacycle,21i molecular iodine,21j montmorillonite K-10,21k nano crystalline TiO2,21l etc. have been used to accomplish this condensation. However, there is still a plenty of room to conceive new well-designed, inexpensive and sustainable approach in addition to current catalytic methodologies.

In continuation of our work on the development of green methodologies using SILP catalysts,22 we report herein an expedient synthesis of oxazolones using cellulose supported ionic liquid phase catalyst.

Results and discussion

In the synthesis of cellulose supported ionic liquid phase catalyst (Scheme 1), aluminum oxide was dispersed on the cellulose (1) with a good degree of adhesion to form cell–Al2O3 composite (2) using literature procedure.23 The inherent ability of surface Al–OH groups of 2 to form stable Al–O–Si bonds with Si–OR groups of (3-chloropropyl)triethoxysilane allowed the synthesis of chloropropyl cellulose (3) with a good degree of organofunctionalization. The ferrocenylmethyl imidazole (4) was then covalently anchored in the cellulose matrix with the help of tethered chloropropyl group by quaternization reaction to yield azolium salt acronymed as [CellFemImi]Cl (5). The anion metathesis reaction of 5 with aqueous solution of ammonia resulted in the desired cellulose supported ionic liquid phase catalyst acronymed as [CellFemImi]OH (6).
image file: c6ra03873e-s1.tif
Scheme 1 Synthesis of [CellFemImi]OH catalyst.

The reactions involved in the synthesis of [CellFemImi]OH (6) were monitored by using FTIR and FTRAMAN spectroscopy. The reaction of 3 with 4 was supervised by FTRAMAN spectroscopy. The intensities of peaks at 605 cm−1 (C–Cl stretching) and 1291 cm−1 (wagging band of CH2–Cl) decreased considerably whereas the peaks at 466 cm−1 (stretching band of Fe–Cp), 1234 cm−1, 1338 cm−1, 1438 cm−1 (stretching modes of imidazolium ring) and 3115 cm−1 (C–H stretching of Cp ring) appeared after 72 h reflecting the confinement of 4 on cellulose matrix. The anion metathesis reaction was monitored by using FTIR spectroscopy. The FTIR spectrum of the 6 displayed characteristic stretching band of medium intensity of O–H group at 3345 cm−1 and a peak of weak intensity at 703 cm−1 revealing the considerable replacement of Cl by OH during the anion metathesis reaction. The formation of 6 was further corroborated by recording 13C CP-MAS spectrum which displayed peaks at 138.5 (s, imidazolium C-2), 127 (s, imidazolium C-4), 120 (s, imidazolium C-5), 113 (bs, C-1 of cellulose), 90 (bs, C-4 of cellulose), 72–76 (m, C-2,3,5 of cellulose), 67 (bs, C-6 of cellulose), 70 (s, non substituted Cp ring carbons of ferrocene), 78 (s, substituted Cp ring carbons of ferrocene), 49 (s, 1C, [double bond, length as m-dash]N–CH2–CH2–CH2), 28 (s, 1C, [double bond, length as m-dash]N–CH2CH2–CH2), 8.0 (s, 1C, –CH2–Si) confirming the proposed structure.

An EDX elemental analysis of 5 revealed grafting of 0.46 mmol of ferrocenylmethyl imidazolium units per g catalyst. The quantification of hydroxyl groups in 6 was done using volumetric titration analysis24 and was found to be 0.31 mmol g−1 catalyst.

The FESEM investigations were carried out to study size and morphology of [CellFemImi]OH (6). The FESEM image of 6 is shown in Fig. 1. The FESEM image clearly shows fibrous morphology of catalyst particles with length in the range of several hundred nanometers up to a few micrometers.


image file: c6ra03873e-f1.tif
Fig. 1 FESEM of [CellFemImi]OH.

The X-ray diffraction (XRD) pattern of chloropropyl cellulose, 5 and [CellFemImi]OH (6) is shown in Fig. 2. The XRD profiles displayed major reflections at 2θ = 14.6°, 16.3°, 22.7° and 34.4° resembling XRD pattern of cellulose confirming that microcrystallinity is maintained in chloropropyl cellulose, 5 and 6 In addition, the decreased peak intensities in 5 and 6 revealed surface destruction of cellulose due to confinement of ionic liquid like unit.25


image file: c6ra03873e-f2.tif
Fig. 2 XRD patterns of chloropropyl cellulose, 5 and 6.

The thermal stability profile of [CellFemImi]OH (6) was analyzed by using TGA-DSC analysis in the temperature range of 25–1000 °C (Fig. 3). The initial weight loss of 8.1% is attributed to the loss of physisorbed water associated with ionic liquid like unit through the hydrogen bonding. The second steep weight loss of ∼61% in the temperature range of 280–330 °C is ascribed to collective loss of ionic liquid like unit and combustible organic materials from crystalline cellulose. The subsequent weight loss of 16.60% is assigned to the decomposition of cellulose units through the formation of levoglucosan and other volatile compounds. The observations are in good agreement with the TGA profile of cellulose reported in the literature.26


image file: c6ra03873e-f3.tif
Fig. 3 TGA profile of [CellFemImi]OH.

Our next task was to evaluate catalytic efficiency of [CellFemImi]OH (6) in the synthesis of oxazolones. Initially, to optimize the reaction conditions, hippuric acid (7, 1 mmol), 4-nitrobenzaldehyde (8c, 1 mmol) and acetic anhydride (3 mmol) were chosen as model substrates for the synthesis of oxazolones in the presence of a catalytic amount of 6 (100 mg) in various solvents at room temperature (Table 1). The model reaction afforded corresponding (4E)-4-(4-nitrobenzylidene)-2-phenyloxazol-5-(4H)-one (9c) in significantly lower yields in CH2Cl2, CHCl3, CH3CN, THF and water (Table 1, entries 1–4 and 12). Ethanol was found to be the best solvent as it furnished the corresponding product in excellent yield in much shorter time (Table 1, entry 6).

Table 1 Optimization of reaction conditions in the synthesis of oxazol-5-onesa

image file: c6ra03873e-u1.tif

Entry Solvent Catalyst (mg) Time (h) Yieldb (%)
a Optimal reaction conditions: 7 (1 mmol), 8c (1 mmol), Ac2O (3 mmol), solvent (5 ml) and [CellFemImi]OH (100 mg).b Isolated yields after column chromatography.
1 CH2Cl2 100 20 40
2 CHCl3 100 18 30
3 CH3CN 100 15 48
4 THF 100 14 34
5 Ethanol 50 8 61
6 Ethanol 100 4 89
7 Ethanol 150 4 90
8 Ethanol 200 4 90
9 Methanol 100 12 63
10 DMF 100 15 51
11 1,4-Dioxane 100 16 52
12 Water 100 15 42


The effect of catalyst loading on the model reaction was also investigated. As shown in Table 1, the yield of product increased by increasing quantity of catalyst from 50 to 100 mg (Table 1, entries 5 and 6). However, further increase in the amount of the catalyst did not showed significant effect on the product yield and reaction time (Table 1, entries 7 and 8). Thus, 100 mg of 6 was selected as optimal catalyst loading for further studies.

The generality of the protocol was established by carrying out reactions of several diversified aldehydes with hippuric acid and acetic anhydride under optimized reaction conditions. It was interesting to note that all the aromatic aldehydes containing various substituents (Table 2, entries a–l) reacted efficiently affording the corresponding oxazolones in excellent yields (Table 2). It is noteworthy to mention that there was no influence of electronic nature of substituents on the aryl ring on the yield of products as aromatic aldehydes with electronic donating as well as electron withdrawing groups resulted in the formation of products in nearly quantitative yields. The identity of all the products was ascertained on the basis of 1H NMR, 13C NMR, FTIR and mass spectroscopy. The spectroscopic data is in consistent with the proposed structures and in harmony with the literature values.27

Table 2 [CellFemImi]OH catalyzed synthesis of oxazolonesaimage file: c6ra03873e-u2.tif
Entry Ar 8 Product 9 Time (h) Yieldb (%) Melting point (°C)
a Optimal reaction conditions: 7 (1 mmol), 8 (1 mmol), Ac2O (3 mmol), EtOH (5 ml) and [CellFemImi]OH (100 mg).b Isolated yields after column chromatography.
a C6H4 image file: c6ra03873e-u3.tif 4 89 165[thin space (1/6-em)]27
b 3-NO2–C6H4 image file: c6ra03873e-u4.tif 5 85 173[thin space (1/6-em)]27
c 4-NO2–C6H4 image file: c6ra03873e-u5.tif 5 89 241[thin space (1/6-em)]27
d 2-Cl–C6H4 image file: c6ra03873e-u6.tif 4 84 163[thin space (1/6-em)]27
e 4-Cl–C6H4 image file: c6ra03873e-u7.tif 4 87 196[thin space (1/6-em)]27
f 4-Br–C6H4 image file: c6ra03873e-u8.tif 5 89 203[thin space (1/6-em)]27
g 4-Me–C6H4 image file: c6ra03873e-u9.tif 5 86 146[thin space (1/6-em)]27
h 4-F–C6H4 image file: c6ra03873e-u10.tif 6 88 185[thin space (1/6-em)]27
i 4-MeO–C6H4 image file: c6ra03873e-u11.tif 4 86 161[thin space (1/6-em)]27
j image file: c6ra03873e-u12.tif image file: c6ra03873e-u13.tif 6 82 171[thin space (1/6-em)]27
k image file: c6ra03873e-u14.tif image file: c6ra03873e-u15.tif 6 80 174[thin space (1/6-em)]27
l 3-CHO–C6H4 image file: c6ra03873e-u16.tif 5 85 135


A plausible mechanism for the formation of oxazolones catalyzed by [CellFemImi]OH (6) is shown in Fig. 4. Initially, 2-phenyl-5-oxazolone is generated by cyclocondensation of hippuric acid in the presence of acetic anhydride as dehydrating agent. The catalyst plays a dual role during catalysis. It activates carbonyl group of aromatic aldehydes by the hydrogen bonding through C2 proton of imidazolium cation as well as acts as a base generating carbanion of 2-phenyl-5-oxazolone. The further nucleophilic attack of carbanion on activated carbonyl group followed by dehydration results in the formation of desired oxazolone.


image file: c6ra03873e-f4.tif
Fig. 4 Plausible mechanism for the synthesis of oxazolones using [CellFemImi]OH.

The leaching of [CellFemImi]OH (6) was studied via ICP-AES. A small amount of organic moieties (<1.6%) were detected leaching into the solvent indicating that most of the ionic liquid like unit remains hooked upon the support. The observed minute leaching could be due to small fraction of ionic liquid like units resided on the outer surface of crystalline cellulose particles. This suggests that ionic liquid like unit containing catalytically active hydroxyl anion is significantly entrenched in crystalline framework of cellulose making 6 leaching defiant for a high-quality reclamation and reusability.

To determine heterogeneity of [CellFemImi]OH (6), hot filtration test was carried out for the model reaction. After 50% conversion (GC), the reaction mass was divided, with one half separated (by simple filtration) into a separate reaction flask. The reaction mixture containing 6 furnished to a completion whereas filtered portion did not exhibit any improvement in the yield of product beyond 50% even after prolonged reaction time confirming the heterogeneous nature of 6.

In order to assess recyclability and reusability of [CellFemImi]OH (6), the model reaction was performed under optimized conditions. An important feature of 6 was its easy and reliable separation from the reaction mixture. The catalyst was separated from reaction mass by simple filtration and reused after reactivation that involved washing with the reaction solvent to remove any adhered species and drying at 60 °C. It is noteworthy to mention that the 6 showed appreciating recycling performance as the corresponding yields started at 89% and reached 84% at the fifth run without extended reaction time (Fig. 5). The slight loss in the yields of the products even after reactivation is likely to be due to agglomeration of support particles into larger crystallites which limits reaching of reacting molecules to the active catalytic site. The mechanical stability of 6 was confirmed from its post catalytic FTIR and CP/MAS 13C spectroscopy analysis. The FTIR and CP/MAS 13C spectra of spent catalyst were similar to that of fresh catalyst confirming the intactness of organic functional groups in the 6.


image file: c6ra03873e-f5.tif
Fig. 5 Recyclability of [CellFemImi]OH.

Present study demonstrates the potential application of SILP catalyst based on refined cellulose as support. This work is model study for its extension to make generalized methods using SILP catalysts for organic transformations through use of natural resources such as raw wood dust, crustacean shells, etc. besides the use of refined cellulose. Recently, some efforts have already been made in this direction.28 Our further research work is focused to design and develop new SILP catalysts using above mentioned natural resources to bring various organic transformations under the umbrella of this novel approach to make synthetic chemistry more sustainable.

Conclusion

In conclusion, we have successfully synthesized a novel cellulose supported ionic liquid phase catalyst containing hydroxide ion and employed in the synthesis of oxazolones by the cyclocondensation of aryl aldehydes with hippuric acid and acetic anhydride. Use of eco benign solvent, excessive product yields, ease of separation and reusability of catalyst makes this protocol a high quality alternative over the other reported methodologies.

Experimental

General

Melting points were determined in an open capillary and are uncorrected. All reactions were carried out under air atmosphere in dried glasswares. Infrared spectra were measured with a Perkin-Elmer one FTIR spectrophotometer. The samples were examined as KBr discs ∼5% w/w. Raman spectroscopy was done by using Bruker FTRAMAN (MultiRAM) spectrometer. 1H NMR and 13C NMR spectra were recorded on a Bruker AC (300 MHz for 1H NMR and 75 MHz for 13C NMR) spectrometer using CDCl3 as solvent and tetramethylsilane (TMS) as an internal standard. Chemical shifts (δ) are expressed parts per million (ppm) values with tetramethylsilane (TMS) as the internal reference and coupling constants are expressed in hertz (Hz). CP/MAS 13C NMR spectrum were recorded on Bruker 500 type FT-NMR spectrometer under prescribed operating conditions. Mass spectra were recorded on a Shimadzu QP2010 GCMS. The thermal gravimetric analysis (TGA) curves were obtained by using the instrument TA SDT Q600 in the presence of static air at a linear heating rate of 10 °C min−1 from 25 °C to 1000 °C. XRD pattern was taken by using Bruker D2 Phaser. FESEM was done using HITACHI S-4800. Elemental analyses were performed on EURO EA3000 vectro model. All the chemicals were obtained from local suppliers as were used without further purification and 1-N-ferrocenylmethyl imidazole was synthesized using reported procedure.29

Preparation of the cell–Al2O3 composite (2)

The cell–Al2O3 composite (2) was prepared as per the reported procedure.23 A mixture of cellulose (15 g) and aluminum chloride hexahydrate (15 g) in water (200 ml) was stirred for 12 hours. The mixture was filtered and the solid was exposed to ammonia gas, washed with water and dried under vacuum at room temperature. The amount of aluminum was determined by calcining 0.300 g of 2 to 600 °C for 8 h and the residue weighed as Al2O3, which was found to be 3.27 wt%, corresponding to 0.69 mmol g−1 aluminium.

Preparation of chloropropyl cellulose (3)

A mixture of 2 (10 g) and (3-chloropropyl)triethoxysilane (9.6 g, 40 mmol) in toluene (30 ml) was refluxed for 24 h. The mixture was filtered and the resultant solid was washed with copious amount of toluene and dried in vacuum at room temperature. FTIR (KBr, thin film): ν = 3366, 2901, 1428, 1372, 1281, 1236, 1031, 898, 703, 629, 513 cm−1; FTRAMAN (KBr): ν = 2898, 1481, 1375, 1117, 1094, 898, 610, 566, 515, 431 cm−1; elemental analysis observed: % C 74.03, % O 22.04, % Al 1.84, % Cl 2.09; loading: 0.59 mmol functional group per g of cellulose.

Preparation of [CellFemImi]Cl (5)

A mixture of 3 (5.0 g) and 1-N-ferrocenylmethyl imidazole 4 (2.65 g, 10 mmol) in DMF (25 ml) was heated at 80 °C. After 48 h, the solid was filtered, washed with DMF (3 × 50 ml), MeOH (3 × 50 ml), CH2Cl2 (3 × 50 ml) and dried in vacuum at room temperature to afford of [CellFemImi]Cl (5). FTIR (KBr, thin film): ν = 3346, 2963, 2901, 1456, 1428, 1371, 1281, 1112, 1059, 703, 665, 560 cm−1; FTRAMAN (KBr): ν = 3235, 2898, 1471, 1330, 1240, 1081, 1089, 987, 768, 605, 555, 443 cm−1; elemental analysis observed: % C 61.2, % N 1.28, % Al 1.2, % Si 0.23, % Fe 0.27; loading: 0.46 mmol functional group per g of cellulose.

Preparation of [CellFemImi]OH (6)

[CellFemImi]Cl (3.0 g) was suspended in 30 ml of an aqueous solution of NH3. The system was stirred for 48 h at room temperature, Afterwards the polymer was filtered and washed with MeOH (3 × 20 ml), MeOH[thin space (1/6-em)]:[thin space (1/6-em)]H2O (1[thin space (1/6-em)]:[thin space (1/6-em)]1) (3 × 20 ml), H2O (3 × 20 ml) and MeOH (3 × 20 ml) and dried under vacuum at 50 °C for 48 h to afford [CellFemImi]OH (6). FTIR (KBr, thin film): ν = 3345, 3280, 2964, 2901, 2853, 1633, 1480, 1455, 1372, 1356, 1318, 1281, 1163, 1112, 1059, 1033, 664, 560, 441 cm−1; FTRAMAN (KBr): ν = 3235, 3115, 2899, 1523, 1475, 1438, 1371, 1234, 1085, 466 cm−1; 13C CP-MAS NMR (500 MHz): δ 138.5 (s), 127 (s), 120 (s), 113 (bs), 90 (bs), 72–76 (m), 67 (bs), 70 (s), 78 (s), 49 (s), 28 (s), 8.0 (s); elemental analysis observed: % C 61.31, % N 1.19, % Al 1.21, % Si 0.21, % Fe 0.28; loading: 0.31 mmol OH-groups per g cellulose matrix.

General procedure for the synthesis of oxazolones

A mixture of aryl aldehyde (1 mmol), hippuric acid (1 mmol) and acetic anhydride (3 mmol) in presence of 6 (100 mg, 0.106 mmol) was stirred in ethanol at room temperature. After the completion of reaction, the reaction mass was filtered and the solid washed with ethanol to afford crude product which was purified by column chromatography (n-hexane/EtOAc = 8[thin space (1/6-em)]:[thin space (1/6-em)]2).

Spectral data

4-(4-Benzylidene)-2-phenyl-5-(4H)-oxazolone (Table 2, product 9a). Yellow solid; mp 165 °C (lit., 166 °C);27 FTIR (KBr, thin film): ν = 3450, 3415, 1796, 1659, 1545, 1475, 859, 760 cm−1; 1H NMR (CDCl3, 300 MHz): δ 7.27 (s, 1H), 7.42–7.58 (m, 6H), 8.20–8.24 (m, 4H) ppm; 13C NMR (CDCl3, 75 MHz): δ 166.0, 160.9, 135.5, 131.7, 131.2, 129.8, 129.2, 128.9, 128.7, 128.0 ppm; mass (EI) m/z: 249 [M]+; anal. calcd for C16H11NO2: % C 77.10, % H 4.45, % N 5.62, observed: % C 77.06, % H 4.42, % N 5.65.
4-(3-Nitrobenzylidene)-2-phenyl-5-(4H)-oxazolone (Table 2, product 9b). Pale yellow solid; mp 173 °C (lit., 175 °C);27 FTIR (KBr, thin film): ν = 3410, 1810, 1650, 1536, 1430, 860, 721 cm−1; 1H NMR (CDCl3, 300 MHz): δ 9.29 (t, J = 1.6 Hz, 1H), 8.44 (d, J = 7.7 Hz, 1H), 8.26 (dd, J = 2.4, 8.1 Hz, 1H), 8.19–8.22 (m, 2H), 7.67 (m, 2H), 7.55 (m, 2H), 7.26 (s, 1H) ppm; 13C NMR (CDCl3, 75 MHz): δ 166.1, 160.1, 148.0, 136.0, 131.1, 129.7, 129.4, 129.1, 128.7, 121.1, 120.4, 112.2 ppm; mass (EI) m/z: 294 [M]+; anal. calcd for C16H10N2O4: % C 65.31, % H 3.43, % N 9.52, observed: % C 65.35, % H 3.41, % N 9.54.
4-(4-Nitrobenzylidene)-2-phenyl-5-(4H)-oxazolone (Table 2, product 9c). Pale yellow solid; mp 241 °C (lit., 239 °C);27 FTIR (KBr, thin film): ν = 3460, 1756, 1652, 1547, 1465, 854, 765 cm−1; 1H NMR (CDCl3, 300 MHz): δ 8.29–8.32 (m, 2H), 8.34–8.37 (m, 2H), 8.24 (dd, J = 1.2, 8.6 Hz, 2H), 7.71–7.73 (m, 1H), 7.61 (dd, J = 4.7, 10.9 Hz, 2H), 7.27 (s, 1H) ppm; 13C NMR (CDCl3, 75 MHz): δ 166.3, 160.4, 147.3, 141.1, 131.4, 131.0, 129.7, 129.1, 128.8, 127.1, 121.2, 112.3 ppm; mass (EI) m/z: 294 [M]+; anal. calcd for C16H10N2O4: % C 65.31, % H 3.43, % N 9.52, observed: % C 65.29, % H 3.40, % N 9.49.
4-(2-Chlorobenzylidene)-2-phenyl-5-(4H)-oxazolone (Table 2, product 9d). Yellow solid; mp 163 °C (lit., 162 °C);27 FTIR (KBr, thin film): ν = 3445, 3305, 1802, 1659, 1547, 1401, 851, 735 cm−1; 1H NMR (CDCl3, 300 MHz): δ 8.94 (dd, J = 1.7, 7.9 Hz, 1H), 8.18 (d, J = 7.5 Hz, 2H), 7.79 (t, J = 7.6 Hz, 1H), 7.67 (m, 2H), 7.58 (m, 3H), 7.50 (s, 1H) ppm; 13C NMR (CDCl3, 75 MHz): δ 166.4, 160.7, 133.3, 131.8, 131.1, 129.6, 129.4, 129.2, 128.7, 128.6, 127.6, 126.2, 112.4 ppm; mass (EI) m/z: 284 [M]+; anal. calcd for C16H10ClNO2: % C 67.74, % H 3.55, % N 4.94, observed: % C 67.70, % H 3.50, % N 4.97.
4-(4-Chlorobenzylidene)-2-phenyl-5-(4H)-oxazolone (Table 2, product 9e). Pale yellow solid; mp 196 °C (lit., 198 °C);27 FTIR (KBr, thin film): ν = 3457, 3360, 1799, 1658, 1597, 1450, 1295, 1071, 855, 760 cm−1; 1H NMR (CDCl3, 300 MHz): δ 8.17 (m, 4H), 7.65 (dd, J = 2.7, 8.6 Hz, 1H), 7.55 (dd, J = 4.9, 10.7 Hz, 2H), 7.47 (dd, J = 2.1, 8.9 Hz, 2H), 7.19 (s, 1H) ppm; 13C NMR (CDCl3, 75 MHz): δ 166.2, 160.4, 133.7, 133.4, 131.4, 131.1, 129.7, 129.1, 128.8, 128.6, 127.6, 112.2 ppm; mass (EI) m/z: 284 [M]+; anal. calcd for C16H10ClNO2: % C 67.74, % H 3.55, % N 4.94, observed: % C 67.70, % H 3.50, % N 4.97.
4-(4-Bromobenzylidene)-2-phenyl-5-(4H)-oxazolone (Table 2, product 9f). Yellow solid; mp 203 °C (lit., 204 °C);27 FTIR (KBr, thin film): ν = 3466, 3075, 1804, 1670, 1547, 1444, 1297, 1044, 840, 753 cm−1; 1H NMR (CDCl3, 300 MHz): δ 8.11 (d, J = 7.5 Hz, 2H), 8.04 (d, J = 8.6 Hz, 2H), 7.61 (dd, J = 8.6, 15.4 Hz, 3H), 7.60 (t, J = 7.7 Hz, 2H), 7.18 (s, 1H) ppm; 13C NMR (CDCl3, 75 MHz): δ 166.1, 160.7, 134.0, 131.8, 131.2, 129.7, 129.1, 128.7, 128.5, 122.2, 112.7 ppm; mass (EI) m/z: 328 [M]+; anal. calcd for C16H10BrNO2: % C 58.56, % H 3.07, % N 4.27, observed: % C 58.59, % H 3.09, % N 4.29.
4-(Methylbenzylidene)-2-phenyl-5-(4H)-oxazolone (Table 2, product 9g). Pale yellow solid; mp 146 °C (lit., 148 °C);27 FTIR (KBr, thin film): ν = 3470, 3325, 2910, 1809, 1659, 1520, 1434, 1270, 1034, 870, 745 cm−1; 1H NMR (CDCl3, 300 MHz): δ 8.13 (dd, J = 1.3, 8.5 Hz, 2H), 8.12 (d, J = 8.3 Hz, 2H), 7.63 (m, 1H), 7.55 (m, 2H), 7.29 (d, J = 8.2 Hz, 2H), 7.25 (s, 1H), 2.39 (s, 3H) ppm; 13C NMR (CDCl3, 75 MHz): δ 166.2, 160.3, 137.3, 132.0, 131.4, 131.0, 129.7, 129.4, 128.9, 128.7, 126.1, 112.2, 24.1 ppm; mass (EI) m/z: 263 [M]+; anal. calcd for C17H13NO2: % C 77.55, % H 4.98, % N 5.32, observed: % C 77.52, % H 5.02, % N 5.35.
4-(4-Fluorobenzylidene)-2-phenyl-5-(4H)-oxazolone (Table 2, product 9h). Pale yellow solid; mp 185 °C (lit., 183 °C);27 FTIR (KBr, thin film): ν = 3401, 3315, 1804, 1668, 1522, 847, 740 cm−1; 1H NMR (CDCl3, 300 MHz): δ 8.45 (dd, J = 5.9, 8.8 Hz, 2H), 8.17 (d, J = 8.3 Hz, 2H), 7.76 (dd, J = 7.1, 14.4 Hz, 1H), 7.67 (t, J = 7.5 Hz, 2H), 7.22 (s, 1H), 7.19 (t, J = 8.6 Hz, 2H). ppm; 13C NMR (CDCl3, 75 MHz): δ 166.1, 162.3, 160.4, 131.8, 131.2, 130.7, 129.6, 129.1, 128.8, 128.2, 115.1, 112.3 ppm; mass (EI) m/z: 267 [M]+; anal. calcd for C16H10FNO2: % C 71.91, % H 3.77, % N 5.24, observed: % C 71.89, % H 3.79, % N 5.22.
4-(4-Methoxybenzylidene)-2-phenyl-5-(4H)-oxazolone (Table 2, product 9i). Yellow solid; mp 161 °C (lit., 159 °C);27 FTIR (KBr, thin film): ν = 3456, 3401, 3035, 2950, 1805, 1760, 1652, 1545, 1076, 803, 775 cm−1; 1H NMR (CDCl3, 300 MHz): δ 8.19 (ddd, J = 2.2, 4.1, 8.4 Hz, 4H), 7.56 (m, 1H), 7.55 (m, 2H), 7.24 (s, 1H), 7.01 (m, 2H), 3.91 (s, 3H) ppm; 13C NMR (CDCl3, 75 MHz): δ 166.4, 160.7, 159.7, 131.4, 131.0, 129.5, 129.1, 128.7, 127.4, 127.1, 114.0, 112.1, 55.7 ppm; mass (EI) m/z: 279 [M]+; anal. calcd for C17H13NO2: % C 73.11, % H 4.69, % N 5.02, observed: % C 73.14, % H 4.72, % N 5.05.
4-(2-Thiophenecarboxylidene)-2-phenyl-5-(4H)-oxazolone (Table 2, product 9k). Yellow solid; mp 174 °C (lit., 176 °C);27 FTIR (KBr, thin film): ν = 3411, 3055, 2905, 1798, 1756, 1658, 1554, 1090, 823, 757 cm−1; 1H NMR (CDCl3, 300 MHz): δ 8.05 (dd, J = 1.2, 8.4 Hz, 2H), 7.46 (dd, J = 0.8, 5.1 Hz, 1H), 7.38 (m, 2H), 7.32 (m, 2H), 7.22 (s, 1H), 7.13 (dd, J = 3.8, 5.0 Hz, 1H) ppm; 13C NMR (CDCl3, 75 MHz): δ 167.4, 161.9, 137.6, 135.4, 135.2, 132.8, 131.3, 128.9, 128.5, 128.1, 124.6, 123.9 ppm; mass (EI) m/z: 255 [M]+; anal. calcd for C14H9NO2S: % C 65.87, % H 3.55, % N 5.49, % S 12.56, observed: % C 65.41, % H 3.12, % N 5.10, % S 12.21.
4-(2-Furanylidene)-2-phenyl-5-(4H)-oxazolone (Table 2, product 9j). Yellow solid; mp 171 °C (lit., 169 °C);27 FTIR (KBr, thin film): ν = 1787, 1653, 1599, 1558, 1492, 1454, 1329, 1232, 1156, 1023, 989, 856 cm−1; 1H NMR (CDCl3, 300 MHz): δ 8.16 (t, J = 1.5, 7.2 Hz, 2H), 7.70 (d, J = 1.5 Hz, 1H), 7.58–7.65 (m, 2H), 7.53 (t, 2H), 7.19 (s, 1H), 6.68 (dd, J = 1.8, 1.5 Hz, 1H) ppm; 13C NMR (CDCl3, 75 MHz): δ 167.1, 163.0, 150.5, 146.6, 133.2, 130.4, 128.9, 128.2, 125.5, 120.1, 118.3, 113.8 ppm; mass (EI) m/z: 239 [M]+; anal. calcd for C14H9NO3: % C 70.29, % H 3.79, % N 5.86, observed: % C 69.89, % H 3.46, % N 5.26.
3-((6E)-(5-oxo-2-phenyloxazol-4-(5H)-ylidene)methyl) benzaldehyde (Table 2, product 9l). Yellow solid; mp 135 °C; FTIR (KBr, thin film): ν = 3062, 2926, 2855, 1789, 1654, 1450, 1325, 1295, 1157, 1097, 981, 884, 799 cm−1; 1H NMR (CDCl3, 300 MHz): δ 10.13 (s, 1H), 8.72 (s, 1H), 8.46 (d, J = 7.8 Hz, 1H), 8.20 (t, J = 7.2, 1.5 Hz, 2H), 7.98 (d, J = 7.8 Hz, 1H), 7.64–7.70 (m, 2H), 7.57 (t, J = 7.5, 7.2 Hz, 2H), 7.29 (s, 1H) ppm; 13C NMR (CDCl3, 75 MHz): δ 191.6, 167.1, 164.5, 137.5, 136.9, 134.6, 134.4, 134.2, 133.8, 133.7, 133.5, 131.1, 129.6, 129.4, 129.0, 128.6, 125.2 ppm; mass (EI) m/z: 279 [M]+; anal. calcd for C17H11NO3: % C 73.64, % H 4.00, % N 5.05, observed: % C 73.14, % H 3.66, % N 4.85.

Acknowledgements

The authors thank UGC, New Delhi for financial assistance [F. No. 40-96/2011(SR)].

References

  1. P. T. Anastas and J. C. Warner, Green Chemistry: Theory and Practice, Oxford University Press, New York, 1998, p. 30 Search PubMed.
  2. (a) J. D. Patil, S. A. Patil and D. M. Pore, RSC Adv., 2015, 5, 21396 RSC; (b) P. Forte, A. Sachse, M. Maes, A. Galarneau and D. De Vos, RSC Adv., 2014, 4, 1045 RSC; (c) C. V. Doorslaer, J. Wahlen, P. Mertens, K. Binnemans and D. De Vos, Dalton Trans., 2010, 39, 8377 RSC; (d) C. P. Mehnert, Chem.–Eur. J., 2005, 11, 50 CrossRef PubMed; (e) S. S. Shinde, B. Se Lee and D. Y. Chi, Tetrahedron Lett., 2008, 49, 27 CrossRef.
  3. (a) C. P. Mehnert, R. A. Cook, N. C. Dispenziere and M. Afeworki, J. Am. Chem. Soc., 2002, 124, 12932 CrossRef CAS PubMed; (b) A. Riisager, K. M. Eriksen, P. Wasserscheid and R. Fehrmann, Catal. Lett., 2003, 90, 149 CrossRef CAS.
  4. P. Wasserscheid, J. Ind. Eng. Chem., 2007, 13, 325 CAS.
  5. (a) H. Li, P. S. Bhadury, B. Song and S. Yang, RSC Adv., 2012, 2, 12525 RSC; (b) M. I. Burguete, H. Erythropel, E. Garcia-Verdugo, S. V. Luis and V. Sans, Green Chem., 2008, 10, 401 RSC; (c) G. Rashinkar and R. Salunkhe, J. Mol. Catal. A: Chem., 2010, 316, 146 CrossRef CAS; (d) V. Sans, N. Karbass, M. I. Burguete, V. Compan, E. Garcia- Verdugo, S. V. Luis and M. Pawlak, Chem.–Eur. J., 2011, 17, 1894 CrossRef CAS PubMed.
  6. L. Rodríguez-Pérez, E. Teuma, A. Falqui, M. Gómez and P. Serp, Chem. Commun., 2008, 4201 RSC.
  7. J. Mikkola, P. Virtanen, H. Karhu, T. Salmia and D. Y. Murzin, Green Chem., 2006, 8, 197 RSC.
  8. N. Clousier, R. Moucel, P. Naik, P. J. Madec, A. C. Gaumont and I. Dez, C. R. Chim., 2011, 14, 680 CrossRef CAS.
  9. Y. Qiao, H. Li, L. Hua, L. Orzechowski, K. Yan, B. Feng, Z. Pan, N. Theyssen, W. Leitner and Z. Hou, ChemPlusChem, 2012, 77, 1128 CrossRef CAS.
  10. W. Xia, D. Su, A. Birkner, L. Ruppel, Y. Wang, C. Woll, J. Qian, C. Liang, G. Marginean, W. Brandl and M. Muhler, Chem. Mater., 2005, 17, 5737 CrossRef CAS.
  11. (a) A. H. Tamboli, A. A. Chaugule, F. A. Sheikh, W. J. Chung and H. Kim, Chin. J. Catal., 2015, 36, 1365 CrossRef CAS; (b) S. Martin, R. Porcar, E. Peris, M. I. Burguete, E. G. Verdugo and S. V. Luis, Green Chem., 2014, 16, 1639 RSC; (c) U. Hintermair, G. Francio and W. Leitner, Chem.–Eur. J., 2013, 19, 4538 CrossRef CAS PubMed; (d) B. Karimi and M. Vafaeezdeh, Chem. Commun., 2012, 48, 3327 RSC; (e) N. A. Khan, Z. Hasan and S. H. Jhung, Chem.–Eur. J., 2014, 20, 376 CrossRef CAS PubMed; (f) B. Ni and A. D. Headley, Chem.–Eur. J., 2010, 16, 4426 CrossRef CAS PubMed; (g) A. Riisager, R. Fehrmann, M. Haumann and P. Wasserscheid, Eur. J. Inorg. Chem., 2006, 695 CrossRef CAS.
  12. J. Zhang, T. J. Elder, Y. Pu and A. J. Ragauskas, Carbohydr. Polym., 2007, 69, 607 CrossRef CAS.
  13. S. Sen, J. D. Martin and D. S. Argyropoulos, ACS Sustainable Chem. Eng., 2013, 1, 858 CrossRef CAS.
  14. (a) A. Mohammadinezhad, M. A. Nasseri and M. Salimi, RSC Adv., 2014, 4, 39870 RSC; (b) P. V. Chavan, K. S. Pandit, U. V. Desai, M. A. Kulkarni and P. P. Wadgaonkar, RSC Adv., 2014, 4, 42137 RSC; (c) A. Shaabani, Z. Hezarkhani and S. Shaabani, RSC Adv., 2014, 4, 64419 RSC; (d) D. Baruah, U. P. Saikia, P. Pahari, D. K. Dutta and D. Konwar, RSC Adv., 2014, 4, 59338 RSC; (e) F. Quignard and A. Choplin, Chem. Commun., 2001, 21 RSC.
  15. A. A. Pereira, P. P. deCastro, A. C. de Mello, B. R. V. Ferreira, M. N. Eberlin and G. W. Amarante, Tetrahedron, 2014, 70, 3271 CrossRef CAS.
  16. H. Jiang, M. W. Paixao, D. Monge and K. A. Jørgensen, J. Am. Chem. Soc., 2010, 132, 2775 CrossRef CAS PubMed.
  17. (a) M. Parveen, A. Ali, S. Ahmed, A. M. Malla, M. Alam, P. S. Pereira Silva, M. R. Silva and D. U. Lee, Spectrochim. Acta, Part A, 2013, 104, 538 CrossRef CAS PubMed; (b) C. Cativiela, J. A. Mayoral, A. Avenoza, M. Gonzalez and M. A. Roy, Synthesis, 1990, 12, 1114 CrossRef; (c) P. A. Conway, K. Devine and F. Paradisi, Tetrahedron, 2009, 65, 2935 CrossRef CAS; (d) A. Natsch, H. G. feller, F. Kuhn, T. Granier and D. W. Roberts, Chem. Res. Toxicol., 2010, 23, 1913 CrossRef CAS PubMed; (e) I. Funes-Ardoiz, M. Blanco-Lomas, P. J. Campos and D. Sampedro, Tetrahedron, 2013, 69, 9766 CrossRef CAS.
  18. (a) S. Moorkoth, K. K. Srinivasan and D. Bukka, Elixir Pharmacy, 2013, 54, 12315 Search PubMed; (b) J. Penalva, R. Puchades, A. Maquieira, S. Gee and B. D. Hammock, Biosens. Bioelectron., 2000, 15, 99 CrossRef CAS PubMed; (c) Y. Prayin, B. Rutnakornpituk, U. Wichai, T. Vilaivan and M. Rutnakornpituk, J. Nanopart. Res., 2014, 16, 1 Search PubMed; (d) T. Nakanishi, K. Yamanaka, M. Kakeda, K. Tsuda and H. Mizutani, Arch. Dermatol. Res., 2013, 305, 241 CrossRef CAS PubMed; (e) M. Hatao, T. Hariya, Y. Katsumura and S. Kato, Toxicology, 1995, 98, 15 CrossRef CAS PubMed; (f) B. Balan and D. Bahulayan, Helv. Chim. Acta, 2013, 96, 2251 CrossRef CAS; (g) H. H. Georgey, Egypt. J. Chem., 2007, 50, 455 CAS; (h) M. Francoise, P. Sierra, A. Pierre, M. Burbridge and N. Guilbaud, Bioorg. Med. Chem. Lett., 2002, 12, 1463 CrossRef; (i) A. El-Mekabaty, O. M. O. Habib, H. M. Hassan and E. B. Moawad, Pet. Sci., 2012, 9, 389 CrossRef CAS.
  19. A. K. Mukerjee, Heterocycles, 1987, 26, 1077 CrossRef CAS.
  20. K. V. J. Ahluwalia, Erlenmeyer-Plochl azlactone and amino acid synthesis, comprehensive practical organic chemistry: preparations and quantitative analysis, 2000, p. 82 Search PubMed.
  21. (a) M. Parveen, F. Ahmad, A. M. Malla, S. Azaz, M. R. Silva and P. S. P. Silva, RSC Adv., 2015, 5, 52330 RSC; (b) H. Moghanian, M. Shabanian and H. Jafari, C. R. Chim., 2012, 15, 346 CrossRef CAS; (c) A. R. Khosropour, M. M. Khodaei and S. J. Hoseini Jomor, J. Heterocycl. Chem., 2008, 45, 683 CrossRef CAS; (d) F. M. Istrate, A. K. Buzas, I. D. Jurberg, Y. Odabachian and F. Gagosz, Org. Lett., 2008, 10, 925 CrossRef CAS PubMed; (e) B. R. Madje, M. B. Ubale, J. V. Bharad and M. S. Shingare, S. Afr. J. Chem., 2010, 63, 158 Search PubMed; (f) M. R. P. Norton Matos, P. M. P. Gois, M. L. E. N. Mata, E. J. Cabrita and C. A. M. Afonso, Synth. Commun., 2003, 33, 1285 CrossRef; (g) K. A. Monk, D. Sarap and R. S. Mohan, Synth. Commun., 2000, 30, 3167 CrossRef CAS; (h) S. J. Ahmadi, S. Sadjadi and M. Hosseinpour, Ultrason. Sonochem., 2013, 20, 408 CrossRef CAS PubMed; (i) M. Weber, W. Frey and R. Peters, Chem.–Eur. J., 2013, 19, 8342 CrossRef CAS PubMed; (j) M. B. Madhusudana Reddy and M. A. Pasha, Synth. Commun., 2010, 40, 1895 CrossRef; (k) N. N. Karade, S. G. Shirodkar, B. M. Dhoot and P. B. Waghmare, J. Chem. Res., 2005, 2005, 46 CrossRef; (l) P. Anandgaonker, G. Kulkarni, S. Gaikwad and A. Rajbhoj, Chin. J. Catal. ., 2014, 35, 196 CrossRef CAS.
  22. (a) R. Kurane, J. Jadhav, S. Khanapure, R. Salunkhe and G. Rashinkar, Green Chem., 2013, 15, 1849 RSC; (b) M. Jagadale, P. Bhange, R. Salunkhe, D. Bhange, M. Rajmane and G. Rashinkar, Appl. Catal., A, 2016, 511, 95 CrossRef CAS.
  23. A. M. Lazarin, Y. Gushikem and S. C. deCastro, J. Mater. Chem., 2000, 10, 2526 RSC.
  24. (a) V. K. Ahluwalia and R. Aggarwal, Comprehensive Practical Organic Chemistry: Preparations And Quantitative Analysis, Universities Press (India) Pvt. Limited, 2005 Search PubMed; (b) A. Kumbhar, S. Jadhav, R. Shejwal, G. Rashinkar and R. Salunkhe, RSC Adv., 2016, 6, 19612 RSC.
  25. Q. Pang, L. Wang, H. Yang, L. Jia, X. Pan and C. Qui, RSC Adv., 2014, 4, 41212 RSC.
  26. (a) Y. Wu, Z. Fu, D. Yin, Q. Xu, F. Liu, C. Lu and L. Mao, Green Chem., 2010, 12, 696 RSC; (b) O. W. Guirguis and M. T. H. Moselhey, Nat. Sci., 2012, 4, 57 CAS.
  27. (a) T. Cleary, T. Rawalpally, N. Kennedy and F. Chavez, Tetrahedron Lett., 2010, 51, 1533 CrossRef CAS; (b) S. Paul, P. Nanda, R. Gupta and A. Loupy, Tetrahedron Lett., 2004, 45, 425 CrossRef CAS; (c) T. Cleary, J. Brice, N. Kennedy and F. Chavez, Tetrahedron Lett., 2010, 51, 625 CrossRef CAS.
  28. (a) B. B. F. Mirjalili and R. Z. Reshquiyea, RSC Adv., 2015, 5, 15566 RSC; (b) E. Tahanpesar, S. Elhami and M. Mohammadi, Int. J. Sci. Res. Environ. Sci., 2015, 3, 0038 Search PubMed; (c) N. Yan and X. Chen, Nature, 2015, 524, 155 CrossRef CAS PubMed.
  29. (a) J. K. Lindsay and C. R. Hauser, J. Org. Chem., 1956, 22, 355 CrossRef; (b) Y. Gao, B. Twamley and J. M. Shreeve, Inorg. Chem., 2004, 43, 3406 CrossRef CAS PubMed.

This journal is © The Royal Society of Chemistry 2016