1-Methyl-3-(propyl-3-sulfonic acid)imidazolium triflate supported on magnetic nanoparticles: an efficient and reusable catalyst for synthesis of mono- and bis-isobenzofuran-1(3H)-ones under solvent-free conditions

Abstract

1-Methyl-3-(propyl-3-sulfonic acid)imidazolium triflate supported on magnetic nanoparticles ([HSO₃PMIM]OTf–SiO₂@MNPs) was prepared by immobilization of [HSO₃PMIM]OTf onto the surface of silica-coated Fe₃O₄ nanoparticles and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), and FT-IR techniques. Efficient synthesis of mono- and bis-isobenzofuran-1(3H)-ones was performed in the presence of this catalyst under thermal conditions and MW irradiation. The catalyst could be easily separated by an external magnet and reused six times under thermal conditions and MW irradiation without significant loss of its activity.

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Introduction

During recent years, ionic liquids (ILs) as environmentally-friendly reaction media or catalysts, have received increasing interest due to their distinctive physicochemical properties such as high thermal stability, negligible vapor pressure, non-flammability, and the ability to dissolve many organic and inorganic materials.^1–3 In spite of extensive applications in organic reactions, they suffer from disadvantages such as difficult product separation and catalyst recovery and the use of large amounts of ILs. Such disadvantages limit their usefulness in large scale operation and lead to serious economical and environmental problems. However, these problems can be solved by immobilization ILs on solid supports such as organic polymers, silica, ZrO₂, TiO₂ and Al₂O₃ and mesoporous MCM-41.^4–10 These heterogeneous IL catalysts have many advantages over their unsupported counterpart, such as separation, reusability, and the ability to provide practical conveniences in a continuous system. In addition, magnetic nanoparticles (MNPs) which have found many applications in the fields of biotechnology and biomedicine^11–14 have emerged as viable alternatives to the conventional heterogeneous supports.^15–25 The magnetic separation technology offers many advantages over conventional filtration and other purification methods in which the catalysts can be simply and efficiently recovered from reaction media with the external magnetic field.^{23,24,26–31} This can be considered as a green technology that avoids the consequences brought about by filtration steps.

Isobenzofuran-1(3H)-ones are an important class of compounds possess a wide range of biological properties such as anti-bacterial, anti-convulsant, anti-HIV, anti-asthmatic, anti-tumor, anti-platelet activities^32–37 as well as anesthesia prolongation, and PGF_2α inhibitory properties.^38–41 Because of the applications of these compounds in medicine and in the synthesis of natural products,^42,43 several acidic and basic catalysts such as trifluoroacetic acid (TFA),⁴⁴ trifluoromethanesulfonic acid (HOTf),⁴⁵ montmorillonite K-10,⁴⁶ NaOH,⁴⁷ KOH,⁴⁸ KF–Al₂O₃,⁴⁹ silica-supported preyssler nanoparticles (H₁₄[NaP₅W₃₀O₁₁₀]/nano-SiO₂)⁵⁰ and ZrOCl₂·8H₂O⁵¹ have been reported for their synthesis.

In continuation of our research on the use of efficient catalytic systems in the synthesis of fine chemicals,^52–57 herein, we wish to report a convenient method for the synthesis of mono- and bis-isobenzofuran-1(3H)-ones in the presence of 1-methyl-3-(propyl-3-sulfonic acid)imidazolium triflate supported on magnetic nanoparticles ([HSO₃PMIM]OTf–SiO₂@MNPs) as a highly reusable catalyst under thermal conditions and MW irradiation (Scheme 1). To the best of our knowledge, this is the first report on the application of MNPs supported IL catalyst in the synthesis of these important heterocyclic compounds.

Scheme 1 Synthesis of isobenzofuran-1(3H)-ones catalyzed by [HSO₃PMIM]OTf–SiO₂@MNPs.

Results and discussion

The acidic IL supported on magnetic nanoparticles ([HSO₃PMIM]OTf–SiO₂@MNPs) was prepared according to the procedure shown in Scheme 2. The ionic liquid [HSO₃PMIM]OTf was prepared by quaternization of 1-methyl-3H-imidazole with 1,3-propanesultone, followed by treatment with HOTf. The magnetite nanoparticles (MNPs) was easily prepared via the co-precipitation method described by Massart⁵⁸ and protected with a layer of silica to prevent aggregation.⁵⁹ The coating process was performed by ultrasonic suspending of MNPs in ethanol and added tetraethoxysilane (TEOS) to form a silica shell under basic conditions through a sol–gel method. Ultimately, a mixture of MNPs and [HSO₃PMIM]OTf in dichloromethane was dispersed by sonication for 5 h.

Scheme 2 Preparation of [HSO₃PMIM]OTf–SiO₂@MNPs.

The prepared catalyst was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometery (VSM) and FT-IR techniques. The XRD patterns of Fe₃O₄ magnetic nanoparticles and silica-coated Fe₃O₄ magnetic nanoparticles are shown in Fig. 1. These patterns show the characteristic peaks and relative intensity which are well-matched with those of standard Fe₃O₄ nanoparticles (JCPDS file no. 19-0629). Moreover, the broad peak from 2θ = 20° to 30° is consistent with an amorphous silica phase in the shell of the silica-coated Fe₃O₄ nanoparticles (Fig. 1a).^60,61 The TEM image of [HSO₃PMIM]OTf–SiO₂@MNPs showed dark nano-Fe₃O₄ cores surrounded by grey silica shells (Fig. 2a). The TEM image of the reused catalyst reveals its stability during the reaction (Fig. 2b). The histogram of size distribution shows that the average diameter of nanoparticles is about 8–12 nm (Fig. 2c).

Fig. 1 X-ray diffraction pattern of: (a) SiO₂@MNPs and (b) standard magnetite pattern (JCPDS no. 19-0629).

Fig. 2 TEM images of: (a) [HSO₃PMIM]OTf–SiO₂@MNPs; (b) recovered [HSO₃PMIM]OTf–SiO₂@MNPs and (c) particle size distribution results for [HSO₃PMIM]OTf–SiO₂@MNPs.

The magnetic properties of MNPs, SiO₂@MNPs and [HSO₃PMIM]OTf–SiO₂@MNPs were measured at room temperature from −10 000 to +10 000 Oe. The magnetization curves for these samples are shown in Fig. 3. The saturation magnetization (M_s) values of samples are 70, 35 and 20 emu g⁻¹, respectively. The decreasing of M_s values from MNPs to [HSO₃PMIM]OTf–SiO₂@MNPs could be attributed to the coating of iron oxide magnetic nanoparticles with silica and IL. Furthermore, the magnetization curves of the magnetic nanoparticles display no hysteresis before and after functionalization. These results clearly demonstrate their superparamagnetic characteristics,⁵⁸ which further reinforce by easy separation of these magnetic nanoparticles with an external magnetic field.

Fig. 3 The VSM result for: (a) MNPs; (b) SiO₂@MNPs and (c) [HSO₃PMIM]OTf–SiO₂@MNPs.

Further characterization of the catalyst was performed by FT-IR spectroscopy. The FT-IR spectra of blank SiO₂@MNPs, [HSO₃PMIM]OTf and [HSO₃PMIM]OTf–SiO₂@MNPs are presented in Fig. 4. All these samples show broad bands at around 3424 and 1630 cm⁻¹, that are assigned to the Si–OH group and adsorbed water, respectively, in which band at 1630 cm⁻¹ is overlapped with band at 1655 cm⁻¹ (Fig. 4b and c). The spectra of the SiO₂@MNPs and [HSO₃PMIM]OTf–SiO₂@MNPs exhibit the characteristic bands at about 1099, 948 and 484 cm⁻¹, which are attributed to the stretching vibrations of Si–O–Si and Fe–O, respectively (Fig. 4a and c). Furthermore, in the FT-IR spectra of [HSO₃PMIM]OTf and [HSO₃PMIM]OTf–SiO₂@MNPs, the typical bands at around 1655 cm⁻¹ (C=N), 1572 cm⁻¹ (C=C), 1428 cm⁻¹ (C–H), 1179 and 1030 cm⁻¹ (S=O) were observed (Fig. 4b and c). In addition, the characteristic band at 1247 cm⁻¹ is attributed to the CF₃ group. These results confirm that IL has been successfully supported on the surface of SiO₂@MNPs (Fig. 4c).

Fig. 4 FT-IR spectra of: (a) SiO₂@MNPs; (b) [HSO₃PMIM]OTf, (c) [HSO₃PMIM]OTf–SiO₂@MNPs and (d) the 6-times reused catalyst.

Synthesis of isobenzofuran-1(3H)-ones catalyzed by [HSO₃PMIM]OTf–SiO₂@MNPs

The condensation of phthalaldehydic acid (1 mmol) with acetophenone (1 mmol) was chosen as a model reaction for the optimization of parameters such as the amount of catalyst, temperature, and MW power. The results are summarized in Table 1. Initially, the reaction was examined in the absence of the catalyst at 100 °C; no desired product was obtained under this conditions even after 2.5 h. Then, the reaction was performed in the presence of SiO₂@MNPs and [HSO₃PMIM]OTf and the corresponding product was obtained in 8% and 69% yields, respectively. In order to find the optimum amount of [HSO₃PMIM]OTf–SiO₂@MNPs catalyst, the reaction was performed with different amounts of the catalyst (15, 20, 25, and 30 mg) under solvent-free conditions at 100 °C. The best yield of the desired product was achieved with 25 mg of [HSO₃PMIM]OTf–SiO₂@MNPs. Using lower amount of catalyst resulted in lower yield, while higher amount did not affect the reaction time and yield. To evaluate the influence of temperature, the model reaction was performed in the range of 80–110 °C. It was found that 100 °C was the optimal temperature and the reaction was incomplete at lower temperature. To find the optimized MW power, the model reaction was carried out in the presence of 25 mg catalyst at 550, 600 and 650 W, and the desired product was obtained in 80%, 95% and 95% yields, respectively. Therefore, 600 W and 100 °C was selected as the optimum power and temperature.

Table 1 Optimization of the reaction conditions for the synthesis of isobenzofuran-1(3H)-ones

Entry	Method	T (°C)	Catalyst amount (mg)	Time	Yield^a (%)
a Isolated yield.b Reaction was performed in the presence of SiO2@MNPs.c Reaction was performed in the presence of 0.01 mmol [HSO3PMIM]OTf.
1	Thermal	100	0	2.5 h	0
2^b	Thermal	100	25	2.5 h	8
3^c	Thermal	100	—	2.5 h	69
4	Thermal	100	15	2.5 h	65
5	Thermal	100	20	2.5 h	82
6	Thermal	100	25	2.5 h	95
7	Thermal	100	30	2.5 h	95
8	Thermal	80	25	2.5 h	72
9	Thermal	90	25	2.5 h	83
10	Thermal	110	25	2.5 h	95
11	MW (550 W)	100	25	10 min	80
12	MW (600 W)	100	25	10 min	95
13	MW (650 W)	100	25	10 min	95

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The scope of this protocol was then extended by using a variety of acetophenones to synthesize isobenzofuran-1(3H)-ones. The results are summarized in Table 2. Unsubstituted acetophenone and acetophenones with electron-withdrawing or electron-donating substituents reacted very well with phthalaldehydic acid in the presence of [HSO₃PMIM]OTf–SiO₂@MNPs catalyst under thermal conditions, affording good to excellent yields of the corresponding isobenzofuran-1(3H)-one derivatives (Table 2, entries 1–12). Acid-sensitive ketones such as 2-acetylthiophene and 4-acetylpyridine were also reacted efficiently to give the desired products in high yields (Table 2, entries 13 and 14.). In order to investigate the effect of MW, the reaction of acetophenones with phthalaldehydic acid was performed under the optimized microwave irradiation. Under these conditions, the desired isobenzofuran-1(3H)-ones were obtained in 65–98% yields in very short reaction times (4–12 min) (Table 2). These results clearly demonstrated that the yields were slightly improved, but the reaction times were significantly reduced under microwave irradiation.

Table 2 Synthesis of isobenzofuran-1(3H)-ones catalyzed by [HSO₃PMIM]OTf–SiO₂@MNPs^a

Entry	Ketone	Product	Thermal		MW
			Time (h)	Yield^b (%)	Time (min)	Yield^b (%)
a Reaction conditions: phthalaldehydic acid (1 mmol), acetophenone (1 mmol), catalyst (25 mg), thermal (100 °C) or MW (600 W, 100 °C).b Isolated yield.
1			2.5	95	10	95
2			3	92	12	95
3			1.5	60	8	65
4			1.45	87	4	91
5			3	85	12	90
6			1.5	85	8	97
7			1	90	8	98
8			1.75	95	8	95
9			2	92	7	93
10			2	92	8	96
11			2.5	65	12	75
12			0.75	90	7	93
13			0.75	90	7	93
14			3	88	10	92

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Another noteworthy advantage of this catalytic system lies in the selective reaction of 1,4-diacetylbenzene with phthalaldehydic acid. Using a 1 : 1 molar ratio of 1,4-diacetylbenzene to phthalaldehydic acid, only one acetyl group reacted selectively and the corresponding mono-isobenzofuran-1(3H)-one 5a was obtained in 80% and 95% yields under thermal conditions and MW irradiation, respectively. Whereas, with a 1 : 3 molar ratio of 1,4-diacetylbenzene to phthalaldehydic acid, both acetyl groups reacted and the corresponding bis-isobenzofuran-1(3H)-one 5b was obtained in 85% and 90% yields, under the above mentioned conditions (Scheme 3). To the best of our knowledge, this is the first report on the selective synthesis of mono- and bis-isobenzofuran-1(3H)-one, which shows the efficiency and applicability of this catalytic system.

Scheme 3 Selective synthesis of mono- and bis-isobenzofuran-1(3H)-ones catalyzed by [HSO₃PMIM]OTf–SiO₂@MNPs.

A plausible mechanism for the formation of isobenzofuran-1(3H)-one is proposed in Scheme 4. Initially, [HSO₃PMIM]OTf–SiO₂@MNPs activates the formyl group of phthalaldehydic acid and also catalyzes the keto–enol tautomerization of acetophenone to give A and B, respectively. Nucleophilic attack of B to A furnishes the intermediate C. The intermediate C undergoes intramolecular nucleophilic cyclization in the presence of the catalyst giving the adduct D. Finally, dehydration of D in the presence of the catalyst produces the desired isobenzofuran-1(3H)-one 3 and releases the catalyst for the next run.

Scheme 4 Proposed mechanism for the synthesis of isobenzofuran-1(3H)-ones catalyzed by [HSO₃PMIM]OTf-SiO₂@MNP.

Recyclability of the catalyst

Finally, we turned our attention to the possibility of recycling the catalyst, since the recovery and reuse of the catalyst are highly preferable for a green process. In this respect, the reusability of the catalyst was investigated in the reaction of phthalaldehydic acid with acetophenone under thermal conditions and MW irradiation. At the end of the reaction, the mixture was cooled to room temperature and chloroform (15 mL) was added. The catalyst was easily separated by a permanent magnet, dried and reused for subsequent reactions. The experimental results suggest that there is no appreciable loss in catalytic activity even after sixth recycle (Fig. 5). The comparison of FT-IR spectra of fresh and reused catalyst suggests the stability of the present catalyst during the reaction (Fig. 4d).

Fig. 5 Recycling experiment of [HSO₃PMIM]OTf–SiO₂@MNPs under thermal conditions (red) and MW irradiation (green).

Conclusions

In conclusion, we have developed a convenient, efficient, and environmentally benign procedure for the preparation of isobenzofuran-1(3H)-one derivatives in the presence of [HSO₃PMIM]OTf–SiO₂@MNPs as a highly recyclable catalyst under solvent-free thermal conditions and MW irradiation. Easy work-up, high yields, short reaction times, high atom-economy, environmental acceptability, and use of easy recoverable and reusable catalyst are the significant advantages of the present protocol in the synthesis of these important compounds.

Experimental

General information

The chemicals used in this work were purchased from Fluka and Merck chemical companies. Melting points were determined with a Stuart Scientific SMP2 apparatus. FT-IR spectra were recorded on a Nicolet-Impact 400D spectrophotometer. ¹H NMR (400 and 500 MHz) and ¹³C NMR (100 and 125 MHz) spectra were recorded on a Bruker Avance spectrometer using CDCl₃ and DMSO-d₆ as solvent. X-Ray diffraction (XRD) images were obtained from a Bruker XRD D8 Advance instrument with Co K_α radiation at 40 kV. The transmission electron microscopy (TEM) was carried out on a Philips CM10 transmission electron microscope operating at 200 kV. The magnetic measurements were performed with a vibrating sample magnetometer (VSM) at Meghnatis Daghigh Kavir Co. The microwave system used in these experiments includes the following items: Micro-SYNTH labstation, equipped with a glass door, a dual magnetron system with pyramid shaped diffuser, 1000 W delivered power, exhaust system, magnetic stirrer, ‘quality pressure’ sensor for flammable organic solvents, and a ATCFO fiber optic system for automatic temperature control.

Synthesis of 1-methyl-3-(propyl-3-sulfonic acid)imidazolium triflate supported on magnetic nanoparticles ([HSO₃PMIM]OTf–SiO₂@MNPs)

Synthesis of 1-methyl-3-(propyl-3-sulfonic acid)imidazoliumtriflate ([HSO₃PMIM]OTf) ionic liquid. A mixture of 1-methyl-3H-imidazole (0.82 g, 10 mmol) and 1,3-propanesultone (1.22 g, 10 mmol) was stirred magnetically for 72 h at room temperature. The resulting white solid was washed with diethyl ether (3 × 10 mL) and dried in vacuum to afford the desired zwitterion in 90% yield. Then, trifluoromethanesulfonic acid (1.5 g, 10 mmol) was added to this white solid zwitterion and the mixture was stirred for 2 h at 40 °C. The resulting crude material was washed repeatedly with toluene and diethyl ether and dried in vacuum to give 1-methyl-3-(propyl-3-sulfonic acid)imidazolium triflate ([HSO₃PMIM]OTf) ionic liquid in quantitative yield. ¹H NMR (400 MHz, D₂O): δ 8.54 (s, 1H), 7.36 (dd, 1H, J = 15.2, 8.0 Hz), 7.26 (dd, 1H, J = 18.0, 6.8 Hz), 4.19 (t, 2H, J = 7.2 Hz), 3.73 (s, 3H), 2.77 (t, 2H, J = 7.2 Hz), 2.16 (q, 2H, J = 7.6 Hz). ¹³C NMR (100 MHz, D₂O): δ 137.0, 135.8, 123.5, 121.9, 47.5, 47.0, 35.5, 24.8.

Synthesis of silica-coated Fe₃O₄ nanoparticles (SiO₂@MNPs). Magnetite nanoparticles (MNPs) were prepared according to the reported procedure.⁵⁸ In this manner, FeCl₃·6H₂O (11.0 g) and FeCl₂·4H₂O (4.0 g) were dissolved in 250 mL deionized water under N₂ with vigorous stirring at 85 °C, during which the pH of the solution adjusted to 9 using conc. NH₃·H₂O. The mixture was further stirred for 4 h and the resulting MNPs precipitates were washed with deionized water and ethanol until the pH reached 7. The black precipitate (MNPs) was collected with a permanent magnet. For coating of a layer of silica on the surface of MNPs, the MNPs (2.0 g) in ethanol (400 mL) were sonicated for 30 min at room temperature under N₂. Then, conc. NH₃·H₂O (12.0 mL) and TEOS (4.0 mL) was added sequentially, and the mixture was dispersed for 24 h under the above mentioned conditions. Finally, the black precipitate (SiO₂@MNPs) was collected using a permanent magnet, washed with ethanol three times and dried in a vacuum.

Synthesis of [HSO₃PMIM]OTf–SiO₂@MNPs. 5.0 g of SiO₂@MNPs was dispersed in 50 mL CH₂Cl₂ by sonication for 1 h. Then, a solution of [HSO₃PMIM]OTf (1.0 g) in CH₂Cl₂ (15 mL) was added, and the mixture was sonicated for 5 h. Finally, the [HSO₃PMIM]OTf–SiO₂@MNPs catalyst was separated by a permanent magnet, washed with n-hexane (3 × 15 mL) and dried under vacuum. The loading of the catalyst was determined by elemental analysis to be 14% W.

General procedure for the synthesis of isobenzofuran-1(3H)-ones under thermal conditions and MW irradiation

A mixture of phthaladehydic acid (1 mmol), acetophenone (1 mmol) and [HSO₃PMIM]OTf–SiO₂@MNPs (25.0 mg) was stirred at 100 °C or subjected to MW irradiation (600 W, 100 °C) for the appropriate time according to Table 2. The progress of the reaction was monitored by TLC (eluent: petroleum ether–ethyl acetate, 5 : 2). After completion of the reaction, the mixture was cooled to room temperature, chloroform (15 mL) was added and the catalyst was easily separated by a permanent magnet. The filtrate was evaporated and the crude product was purified by chromatography on silica gel (eluent: petroleum ether–ethyl acetate, 5 : 2) or by recrystallization from acetone and ethanol (1 : 2) to afford the pure product.

3-(2-Oxo-2-phenyl)isobenzofuran-1(3H)-one (3a). Mp: 143–145 °C ((ref. 44) 145 °C). FT-IR (KBr, cm⁻¹): ν_max 3053, 2930, 1629, 1466, 1365, 1335, 1098, 1045, 793. ¹H NMR (400 MHz, CDCl₃): δ 7.93–7.98 (m, 3H), 7.56–7.70 (m, 4H), 7.49–7.54 (m, 2H), 6.20 (t, 1H, J = 6.6 Hz), 3.80 (dd, 1H, J = 17.6, 5.6 Hz), 3.41 (dd, 1H, J = 17.6, 7.6 Hz).

3-[2-(4-Cyclohexylphenyl)-2-oxo-ethyl]isobenzofuran-1(3H)-one (3b). Mp: 188–191 °C. FT-IR (KBr, cm⁻¹): ν_max 3043, 2927, 2790, 1760, 1674, 1605, 1445, 1294, 1088, 972, 826, 760. ¹H NMR (400 MHz, CDCl₃): δ 7.89–7.94 (m, 3H), 7.65–7.68 (m, 1H), 7.49–7.59 (m, 2H), 7.27–7.40 (m, 2H), 6.20 (t, 1H, J = 6.4 Hz), 3.78 (dd, 1H, J = 17.6, 5.6 Hz), 3.37 (dd, 1H, J = 17.6, 7.6 Hz), 2.58 (s, 1H), 1.86–1.95 (m, 4H), 1.78 (d, 1H, J = 12.4 Hz), 1.41–1.58 (m, 4H), 1.28–1.36 (m, 1H). ¹³C NMR (100 MHz, CDCl₃): δ 195.7, 170.2, 154.7, 149.9, 134.2, 134.1, 129.4, 128.4, 127.3, 126.0, 125.7, 122.9, 77.4, 44.8, 43.6, 34.1, 26.7, 26.0.

3-[2-(4-Methoxyphenyl)-2-oxoethyl]isobenzofuran-1(3H)-one (3c). Mp: 118–120 °C ((ref. 48) 120 °C). FT-IR (KBr, cm⁻¹): ν_max 3116, 2966, 1786, 1763, 1607, 1355, 1282, 1048, 940, 838, 751. ¹H NMR (500 MHz, CDCl₃): δ 7.92–7.96 (m, 3H), 7.65–7.68 (m, 1H), 7.53–7.59 (m, 2H), 6.96 (d, 2H, J = 8.8 Hz), 6.18 (t, 1H, J = 6.6 Hz), 3.89 (s, 3H), 3.74 (dd, 1H, J = 17.4, 5.7 Hz), 3.34 (dd, 1H, J = 17.3, 7.5 Hz).

3-[2-(4-Methylphenyl)-2-oxo-ethyl]isobenzofuran-1(3H)-one (3d). Mp: 147–149 °C ((ref. 50) 149 °C). FT-IR (KBr, cm⁻¹): ν_max 2903, 1762, 1673, 1604, 1296, 1082, 942, 800, 763. ¹H NMR (400 MHz, CDCl₃): δ 7.90 (d, 1H, J = 7.6), 7.85–7.87 (m, 2H), 7.64–7.68 (m, 1H), 7.53–7.58 (m, 2H), 7.27–7.29 (m, 2H), 6.18 (t, 1H, J = 6.5 Hz), 3.76 (dd, 1H, J = 17.5, 5.7 Hz), 3.37 (dd, 1H, J = 16.2, 7.5 Hz), 2.42 (s, 3H).

3-[2-(3,4-Dimethoxyphenyl)-2-oxo-ethyl]isobenzofuran-1(3H)-one (3e). Mp: 116–119 °C. FT-IR (KBr, cm⁻¹): ν_max 2965, 1765, 1650, 1469, 1256, 1171, 1034, 941, 750. ¹H NMR (400 MHz, CDCl₃): δ 7.92 (d, 1H, J = 7.6 Hz), 7.65–7.69 (m, 2H), 7.57–7.60 (m, 2H), 7.54 (d, 2H, J = 2.0 Hz), 6.18 (t, 1H, J = 6.6 Hz), 3.96 (s, 3H), 3.95 (s, 3H), 3.75 (dd, 1H, J = 17.2, 6.0 Hz), 3.37 (dd, 1H, J = 17.2, 7.2 Hz). ¹³C NMR (100 MHz, CDCl₃): δ 194.5, 170.2, 153.9, 149.8, 149.2, 134.3, 129.4, 129.3, 125.9, 125.7, 123.2, 122.9, 110.1, 110.0, 77.5, 56.2, 56.0, 43.2.

3-[2-(2-Hydroxyphenyl)-2-oxo-ethyl]isobenzofuran-1(3H)-one (3f). Mp: 134–136 °C ((ref. 47) 134–136 °C). FT-IR (KBr, cm⁻¹): ν_max 3038, 2920, 1773, 1634, 1443, 1297, 1078, 965, 759. ¹H NMR (500 MHz, CDCl₃): δ 12.03 (s, 1H), 7.94 (d, 1H, J = 7.6 Hz), 7.65–7.72 (m, 2H), 7.56–7.59 (m, 2H), 7.51–7.54 (m, 1H), 7.04 (dd, 1H, J = 8.4, 1.0 Hz), 6.90–6.93 (m, 1H), 6.17 (t, 1H, J = 6.5 Hz), 3.8 (dd, 1H, J = 17.6, 6.2 Hz), 3.45 (dd, 1H, J = 17.6, 6.8 Hz).

3-[2-(4-Nitrophenyl)-2-oxo-ethyl]isobenzofuran-1(3H)-one (3g). Mp: 208–210 °C ((ref. 51) 210 °C). FT-IR (KBr, cm⁻¹): ν_max 3104, 2909, 1748, 1689, 1603, 1456, 1320, 1270, 1085, 982, 854, 752. ¹H NMR (400 MHz, CDCl₃): δ 7.93 (d, 1H, J = 7.6), 7.86–7.90 (m, 2H), 7.66–7.74 (m, 3H), 7.55–7.58 (m, 2H), 6.16 (t, 1H, J = 6.2 Hz), 3.72 (dd, 1H, J = 17.0, 5.8 Hz), 3.36 (dd, 1H, J = 17.6, 6.8 Hz).

3-[2-(3-Chlorophenyl)-2-oxo-ethyl]isobenzofuran-1(3H)-one (3h). Mp: 142–144 °C. FT-IR (KBr, cm⁻¹): ν_max 2927, 1754, 1634, 1423, 1227, 1163, 1097, 946, 799. ¹H NMR (400 MHz, CDCl₃): δ 7.76–7.84 (m, 4H), 7.61–7.65 (m, 1H), 7.47–7.55 (m, 2H), 7.37 (t, 1H, J = 6.4 Hz), 6.08 (t, 1H, J = 6.4 Hz), 3.64 (dd, 1H, J = 17.8, 6.6 Hz), 3.42 (dd, 1H, J = 17.8, 6.2 Hz). ¹³C NMR (100 MHz, CDCl₃): δ 194.7, 170.0, 149.4, 137.6, 135.0, 134.4, 133.6, 130.2, 129.5, 128.1, 126.4, 125.8, 125.6, 122.7, 76.9, 42.9.

3-[2-(4-Fluorophenyl)-2-oxo-ethyl]isobenzofuran-1(3H)-one (3i). Mp: 132–134 °C ((ref. 48) 130–133 °C). FT-IR (KBr, cm⁻¹): ν_max 3080, 2965, 2911, 1756, 1681, 1596, 1213, 973, 837. ¹H NMR (500 MHz, CDCl₃): δ 7.98–8.00 (m, 2H), 7.92 (d, 1H, J = 7.6 Hz), 7.67 (t, 1H, J = 7.5 Hz), 7.53–7.57 (m, 2H), 7.15 (t, 2H, J = 8.5), 6.16 (t, 1H, J = 6.5 Hz), 3.74 (dd, 1H, J = 17.5, 6.0 Hz), 3.38 (dd, 1H, J = 17.5, 7.0 Hz).

3-[2-(4-Chlorophenyl)-2-oxo-ethyl]isobenzofuran-1(3H)-one (3j). Mp: 144–146 °C ((ref. 44) 146 °C). FT-IR (KBr, cm⁻¹): ν_max 3070, 2924, 1753, 1680, 1590, 1217, 1085, 988, 821. ¹H NMR (500 MHz, CDCl₃): δ 7.89–7.92 (m, 3H), 7.67 (t, 1H, J = 7.5 Hz), 7.54–7.57 (m, 2H), 7.46 (d, 2H, J = 8.6 Hz), 6.16 (t, 1H, J = 6.5 Hz), 3.73 (dd, 1H, J = 17.5, 6.0 Hz), 3.38 (dd, 1H, J = 17.5, 7.0 Hz).

3-[2-(4-Bromophenyl)-2-oxo-ethyl]isobenzofuran-1(3H)-one (3k). Mp: 146–148 °C. FT-IR (KBr, cm⁻¹): ν_max 3040, 2965, 1760, 1681, 1583, 1405, 1290, 1215, 965, 756. ¹H NMR (500 MHz, CDCl₃): δ 7.92 (d, 1H, J = 7.8 Hz), 7.81–7.83 (m, 2H), 7.66–7.69 (m, 1H), 7.62–7.64 (m, 2H), 7.54–7.57 (m, 2H), 6.16 (t, 1H, J = 6.5 Hz), 3.72 (dd, 1H, J = 17.5, 6.0 Hz), 3.37 (dd, 1H, J = 17.5, 7.0 Hz).

3-[2-(4-Iodophenyl)-2-oxo-ethyl]isobenzofuran-1(3H)-one (3l). Mp: 174–175 °C. FT-IR (KBr, cm⁻¹): ν_max 3085, 2903, 1758, 1678, 1457, 1295, 1076, 987, 765. ¹H NMR (500 MHz, CDCl₃): δ 7.93 (d, 1H J = 7.7 Hz), 7.86–7.88 (m, 2H), 7.66–7.70 (m, 3H), 7.57 (t, 2H, J = 7.0 Hz), 6.16 (t, 1H, J = 6.3 Hz), 3.72 (dd, 1H, J = 17.6, 5.8 Hz), 3.37 (dd, 1H, J = 17.6, 6.8 Hz). ¹³C NMR (125 MHz, CDCl₃): δ 195.3, 170.0, 149.6, 138.2, 135.5, 134.3, 129.5, 129.4, 125.9, 122.7, 102.1, 76.9, 74.0, 43.6.

3-(2-Oxo-2-thiophen-2-yl-ethyl)isobenzofuran-1(3H)-one (3m). Mp: 132–135 °C. FT-IR (KBr, cm⁻¹): ν_max 3084, 2926, 1767, 1654, 1519, 1291, 1067, 855, 754. ¹H NMR (400 MHz, CDCl₃): δ 7.94 (d, 1H, J = 7.6 Hz), 7.67–7.72 (m, 3H), 7.55–7.60 (m, 2H), 7.17 (s, 1H), 6.17 (t, 1H, J = 6.4 Hz), 3.70 (dd, 1H, J = 16.6, 6.0 Hz), 3.35 (dd, 1H, J = 16.8, 6.8 Hz). ¹³C NMR (100 MHz, acetone-d₆): δ 189.7, 170.4, 150.8, 144.8, 135.6, 135.0, 134.3, 130.2, 129.4, 127.0, 125.9, 123.7, 77.8, 44.3.

3-[2-Oxo-2-(pyridine-4-yl)ethyl]isobenzofuran-1(3H)-one (3n). Mp: 168–170 °C. FT-IR (KBr, cm⁻¹): ν_max 3071, 2959, 2928, 2859, 1770, 1730, 1600, 1465, 1352, 1285, 1125, 1070, 916, 747. ¹H NMR (500 MHz, CDCl₃): δ 8.82–8.83 (m, 2H), 7.90 (d, 1H, J = 7.6 Hz), 7.66–7.73 (m, 3H), 7.54–7.57 (m, 2H), 6.14 (t, 1H, J = 5.0 Hz), 3.74 (dd, 1H, J = 17.9, 6.3 Hz), 3.43 (dd, 1H, J = 17.9, 6.5 Hz). ¹³C NMR (125 MHz, CDCl₃): δ 195.7, 169.9, 151.2, 149.2, 141.8, 134.4, 128.7, 125.9, 125.8, 122.7, 120.9, 76.5, 43.9.

3-[2-(4-Acetylphenyl)-2-oxo-ethyl]isobenzofuran-1(3H)-one (5a). Mp: 135–137 °C. FT-IR (KBr, cm⁻¹): ν_max 2923, 1758, 1679, 1608, 1403, 1358, 1215, 970, 829, 755. ¹H NMR (400 MHz, CDCl₃): δ 7.60–7.65 (m, 4H), 7.50 (dd, 2H, J = 7.0, 2.2 Hz), 7.45–7.48 (m, 2H), 6.11 (t, 1H, J = 6.4 Hz), 3.72 (dd, 1H, J = 17.6, 6.0 Hz), 3.37 (dd, 1H, J = 17.6, 6.8 Hz), 2.59 (s, 3H). ¹³C NMR (100 MHz, DMSO-d₆): δ 196.7, 196.3, 169.7, 149.7, 139.4, 134.3, 129.3, 128.5, 125.4, 124.9, 123.5, 122.8, 122.3, 76.9, 43.1, 27.0.

3,3′-(1,4-Phenylenebis(2-oxoethane-2,1-diyl))bis(isobenzofuran-1(3H)-one) (5b). Mp: 273–275 °C. FT-IR (KBr, cm⁻¹): ν_max 3094, 1756, 1676, 1294, 1223, 1087, 969, 759, 690. ¹H NMR (400 MHz, DMSO-d₆): δ 8.08–8.18 (m, 4H), 7.86–7.94 (m, 3H), 7.75–7.83 (m, 4H), 7.61–7.69 (m, 1H), 6.14 (dd, 2H, J = 7.8, 3.8 Hz), 3.95 (dd, 2H, J = 18.4, 3.8 Hz), 3.81 (dd, 2H, J = 18.4, 8.4 Hz). ¹³C NMR (100 MHz, DMSO-d₆): δ 206.5, 196.4, 139.8, 138.4, 134.3, 129.3, 124.9, 122.9, 119.1, 117.4, 76.9, 30.6.

Acknowledgements

The authors are grateful to the Research Council of the University of Isfahan for financial support of this work.

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Footnote

† Electronic supplementary information (ESI) available. See DOI: 10.1039/c4ra14112a

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