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Original article
4 (
1
); 11-15
doi:
10.1016/j.arabjc.2010.06.009

Microwave-assisted expeditious hydrolysis of isobenzofuranone derivatives using silica supported acid under organic solvent-free conditions

Laboratory of Organic Chemistry Research, Department of Organic Chemistry, College of Chemistry, University of Kashan, P.O. Box 87317-51167, Kashan, I.R., Iran

*Corresponding author Safari@kashanu.ac.ir (Javad Safari)

Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Available online 15 June 2010

Abstract

Silica sulfuric acid was found to be an efficient, reusable and environment-friendly catalyst for fast hydrolysis of various isobenzofuranone to corresponding 2-ketomethylquinoline derivatives in a high yield under solvent-free using microwave irradiation. As the activator of silica sulfuric acid the wet SiO2 was chosen. The reactions in conventional conditions were compared with the microwave assisted reactions. This approach can prove beneficial since the recovery of solvents from conventional reaction systems always results in some losses.

Keywords

Silica sulfuric acid
Solid acid catalyst
Organic solvent-free
Isobenzofuranone
Microwave irradiation
1

1 Introduction

The hydrolysis of carboxylic acid esters is one of the most studied chemical reactions (Varma et al., 1993). The reported ester hydrolysis could be catalyzed by acid, alkali (Theodorou et al., 2007), molecular iodine (Yadav et al., 2006), Zn(II) complexes Bazzicalupi et al., 2005, and Cu(II) complexes Kou et al., 2004. General acidic hydrolysis of the majority of common esters occurs in the presence of strong liquid protic acids such as HCl, TFA, H2SO4 (Strazzolini et al., 2005) and HNO3 (Strazzolini et al., 2000), as catalysts dissolved in organic solvents. However, many of the above-mentioned liquid acid catalysts are corrosive and often cause heavy environmental pollution because of the difficult separation from the reaction medium. Furthermore, the reactions require long reaction times and often give unsatisfactory yields.

Over the past two decades, microwave-assisted procedures have been successfully employed in a number of synthetic transformations, resulting in rapid and efficient synthesis of different classes of organic compounds. In recent years, the use of solid supports under microwave irradiation has become more popular in synthetic organic chemistry (Varma, 1999; Gershonov et al., 2007) and heterogeneous reactions facilitated by supported reagents on various solid inorganic surfaces have received more attention (Varma and Saini, 1997; Song and Lee, 2002; Bahulayan et al., 2002). In general, solid acid catalysts are mainly based on clay (Varma and Meshram, 1997; Varma et al., 1997) or montmorillonite (Bosch et al., 1995) and silica (Zolfigol et al., 2004, 2005).

In terms of convenience, silica-based catalysts are inexpensive, easy to prepare, and insoluble in most of the organic solvents, which means that they have the advantage of recovery and recycle from various reactions. Recently, silica sulfuric acid has been used as a solid acid catalyst in many reactions such as nitration of aromatic compounds (Riego et al., 1996), aldol condensation (Salehi et al., 2004), acetylization (Mirjalili et al., 2004; Varma et al., 1993), oxidation of alcohols and sulfides (Varma and Dahiya, 1997; Varma et al., 1997), reduction reaction (Varma and Sanini, 1997), desilylation reactions (Varma et al., 1993), direct etherification of trimethylsilylethers (Zolfigol et al., 2003) and so forth.

In continuation of our work on the synthesis of new isobenzofuranone derivatives (Safari et al., 2007), we decided to apply silica sulfuric acid with wet SiO2 as the activator to hydrolysis of 3-[(E)-1-(2-quinolyl)methylidene]-1(3H)-isobenzofuranone derivatives under conventional heating conditions and using microwave irradiation (Scheme 1).

Microwave-assisted hydrolysis of isobenzofuranone derivatives in presence of SSA/Wet SiO2.
Scheme 1
Microwave-assisted hydrolysis of isobenzofuranone derivatives in presence of SSA/Wet SiO2.

2

2 Experimental

2.1

2.1 Materials

Chemicals were purchased from the Merck Chemical Company in high purity. All of the materials were of commercial reagent grade. Silica sulfuric acid was prepared according to the reported procedure (Zolfigol et al., 2005).

2.2

2.2 Apparatus

Melting points were determined in open capillaries using an Electrothermal Mk3 apparatus. The reactions were carried out in a microwave oven (ETHOS 1600, Milestone) with a power of 600 W specially designed for organic synthesis, with continuous stirring. IR spectra were recorded using a Perkin-Elmer FT-IR 550 spectrophotometer. 1H NMR and 13C NMR spectra were recorded on a Bruker DRX-500 spectrometer for sample as indicated with tetramethylsilane as internal reference. UV spectra were recorded on a Hitachi 200-20 spectrophotometer using spectrophotometric grade chloroform (Baker). MS spectra were recorded on a Finnigan MAT 44S, with an ionization voltage of 70 eV. The element analyses (C, H, N) were obtained from a Carlo ERBA Model EA 1108 analyser carried out on Perkin-Elmer 240c analyzer, their results were found to be in good agreement (±0.2%) with the calculated values. Yields refer to isolated products.

2.3

2.3 General synthesis of isobenzofuranone derivatives

Isobenzofuranone (1a–i) were synthesized by the reaction of 2-methyquinoline (1.0 ml, 6.66 mmol), phthalic anhydride (1.0 g, 6.66 mmol) and acetic anhydride (1.5 ml). Mixture was stirred well. The whole mixture was irradiated by microwave oven (ETHOS 1600, Milestone) with a power of 600 W specially designed for organic synthesis as described in Safari et al. (2007).

2.4

2.4 Typical procedure for the hydrolysis of 3-[(E)-1-(2-quinolyl) methylidene]-1(3H)-isobenzofuranone (1a–i)

A mixture of substrate 1a–i (10 mmol; see Table 3 for substrates and stirring times) and silica sulfuric acid (0.1 g) was heated at 100 °C for 50–80 min or irradiated in a microwave oven (max. power 600 W, applied power up to 35%) for 5–20 min. The reaction was monitored by TLC using a 3:7 mixture of ethyl acetate–petroleum ether as an eluent. After completion of the reaction the mixture was cooled to room temperature and the solid materials residue was then washed with acetone and the solvent was evaporated to give the crude product. For further purification it was crystallized from 9:1 acetone–water mixture to afford pure product (2a–i, Table 3).

Table 3 Hydrolysis of isobenzofuranone derivatives to the corresponding enaminone.
Entry R Yield (%) time (min) M.p. (°C)
Δa MWb Found Reported
2a H 43 (80) 88 (20) 154–155 155–156c
2b 4-NO2 51 (60) (51, 50, 48, 47) 93 (10) (92, 90, 89, 87) 165–167
2c 5-NO2 48 (70) 91 (15) 174–177
2d 4,7-F 53 (60) 92 (10) 201–204
2e 4,7-Cl 53 (75) 91 (15) 213–216
2f 5,6-F 52 (50) 95 (7) 224–227
2g 4,5,6,7-F 58 (40) 97 (5) 213–215
2h 4,5,6,7-Cl 51 (60) 95 (10) 223–225
2i 4,5,6,7-Br 49 (75) 91 (15) 234–236
Under classical heating conditions at 100 °C.
Using microwave irradiation.
See reference (Eibner and Hofmann, 1904).

2.5

2.5 Spectral data for new products

2.5.1

2.5.1 2-[2-(2(1H)quinolinylidene)acethyl]benzoic acid (2a, C18H13NO3)

Yield: 88%, mp: 151–153 °C. IR (KBr, cm−1): 3405, 1726, 1640, 1588, 1103 cm−1. 1H NMR (500 MHz, CDCl3): δ = 15.2 (s, 1H, NH enaminone form), 11.7 (s, 1H, OH carboxylic acid), 8.1 (d, 1H, 3J = 9.2 Hz), 7.9 (d, 1H, 3J = 9.2 Hz), 7.7–7.8 (m, 4H), 7.5–7.6 (m, 4H), 7.4 (s, 1H) ppm. 13C NMR (125 MHz, CDCl3): δ = 195.7 (C⚌O), 187.0 (C⚌O), 111.0 (C), 154.3 (CH), 138.5 (C), 138.3 (C), 132.9 (CH), 132.6 (CH), 132.2 (CH), 130.8 (CH), 129.8 (C), 129.3 (CH), 123.8 (CH), 121.0 (C), 120.4 (CH), 119.4 (CH), 117.5 (CH), 98.2 (CH) ppm. MS (70 eV) m/z = 291 (M+•, 100), 273, 217 (26), 143 (16), 170 (22), 143 (48), 76 (23). UV (EtOH): λmax(ɛ) = 413, 314, 233 nm. Anal. Calc. for C18H13NO3: C, 74.22; H, 4.50; N, 4.81. Found: C, 74.11; H, 4.51; N, 4.83%.

2.5.2

2.5.2 3-Nitro-2-[2-(2(1H)quinolinylidene)acethyl]benzoic acid (2b, C18H12N2O5)

Yield: 93%, mp: 165–167 °C. IR (KBr, cm−1): 3409, 1728, 1643, 1535, 1330, 1108 cm−1. 1H NMR (500 MHz, CDCl3): δ = 15.4 (s, 1H, NH enaminone form), 11.8 (s, 1H, OH carboxylic acid), 8.7 (dd, 1H, 3J = 8.6, 4J = 2.0 Hz), 7.9 (d, 1H, 3J = 9.2 Hz), 7.6–7.8 (m, 3H), 7.3–7.4 (m, 4H), 7.1 (s, 1H) ppm. 13C NMR (125 MHz, CDCl3): δ = 196.0 (C⚌O), 187.3 (C⚌O), 154.3 (C), 138.5 (C), 138.0 (CH), 132.6 (C), 132.2 (CH), 129.1 (C), 130.3 (CH), 129.4 (CH), 129.0 (CH), 123.4 (CH), 121.4 (C), 120.9 (CH), 119.0 (CH), 117.0 (C), 111.5 (CH), 98.7 (CH) ppm. MS (70 eV) m/z = 336 (M+•, 100), 337, 338 (26), 318 (16), 262 (22). UV (EtOH): λmax(ɛ) = 414, 316, 232 nm. Anal. Calc. for C18H12N2O5: C, 64.29; H, 3.60; N, 8.33. Found: C, 64.27; H, 2.59; N, 8.30%.

2.5.3

2.5.3 4-Nitro-2-[2-(2(1H)quinolinylidene)acethyl] benzoic acid (2c, C18H12N2O5)

Yield: 91%, mp: 174–177 °C. IR (KBr, cm−1): 3410, 1728, 1648, 1596, 1108 cm−1. 1H NMR (500 MHz, CDCl3): δ = 15.6 (s, 1H, NH enaminone form), 11.9 (s, 1H, OH carboxylic acid), 9.1 (d, 1H, 4J = 2.7 Hz), 8.8 (dd, 1H, 3J = 8.6, 4J = 2.7 Hz), 8.5 (d, 1H, 3J = 8.6 Hz), 7.9 (d, 1H, 3J = 9.4 Hz), 7.5–7.7 (m, 2H), 7.3–7.5 (m, 3H), 7.1 (s, 1H) ppm. 13C NMR (125 MHz, CDCl3): δ = 195.0 (C⚌O), 187.0 (C⚌O), 154.5 (C), 139.0 (C), 138.3 (C), 132.3 (CH), 132.8 (C), 129.6 (CH), 130.8 (CH), 129.9 (C), 129.4 (CH), 123.0 (C), 121.9 (CH), 121.2 (CH), 119.7 (CH), 117.8 (CH), 112.2 (CH), 98.1 (CH) ppm. MS (70 eV) m/z = 336 (M+•, 100), 337, 338 (26), 318 (16), 262 (22). UV (EtOH): λmax(ɛ) = 415, 318, 235 nm. Anal. Calc. for C18H12N2O5: C, 64.29; H, 3.60; N, 8.33. Found: C, 64.27; H, 2.59; N, 8.30%.

2.5.4

2.5.4 3,6-Difluoro-2-[2-(2(1H)quinolinylidene)acethyl]benzoic acid (2d, C18H11F2NO3)

Yield: 92%, mp: 201–204 °C. IR (KBr, cm−1): 3409, 1727, 1648, 1596, 1108 cm−1. 1H NMR (500 MHz, CDCl3): 1H NMR (500 MHz, CDCl3): δ = 15.7 (s, 1H, NH enaminone form), 11.5 (s, 1H, OH carboxylic acid), 8.8 (ddd, 1H, 3J = 9.8, 8.0, 4J = 6.4 Hz), 8.5 (ddd, 1H, 3J = 9.6, 8.0, 4J = 6.4 Hz), 7.7–7.8 (m, 2H), 7.4–7.5 (m, 3H), 7.2 (d, 1H, 3J = 9.2 Hz), 7.0 (s, 1H) ppm. 13C NMR (125 MHz, CDCl3): δ = 195.7 (C⚌O), 187.2 (C⚌O), 167.5 (CF), 154.5 (CF), 164.3 (C), 139.0 (C), 138.3 (CH), 132.8 (CH), 129.6 (CH), 130.8 (CH), 129.9 (CH), 129.4 (C), 123.0 (C), 121.9 (CH), 121.2 (C), 119.7 (CH), 112.2 (CH), 98.1 (CH) ppm. MS (70 eV) m/z = 327 (M+•, 100), 309, 253 (26), 206 (16), 179 (22). UV (EtOH): λmax(ɛ) = 413, 312, 232 nm. Anal. Calc. for C18H11F2NO3: C, 66.06; H, 3.39; N, 4.28. Found: C, 65.96; H, 3.36; N, 4.24%.

2.5.5

2.5.5 3,6-Dichloro-2-[2-(2(1H)quinolinylidene)acethyl]benzoic acid (2e, C18H11Cl2NO3)

Yield: 91%, mp: 213–216 °C. IR (KBr, cm−1): 3410, 1728, 1642, 1593, 1110 cm−1. 1H NMR (500 MHz, CDCl3): 1H NMR (500 MHz, CDCl3): δ = 15.6 (s, 1H, NH enaminone form), 11.6 (s, 1H, OH carboxylic acid), 8.6 (d, 1H, 3J = 8.3 Hz), 8.4 (d, 1H, 3J = 8.3 Hz), 7.9 (d, 1H, 3J = 9.3 Hz), 7.7 (dd, 1H, 3J = 8.2, 4J = 2.3 Hz), 7.2 (d, 1H, 3J = 9.3 Hz), 7.4–7.5 (m, 3H), 7.0 (s, 1H) ppm. 13C NMR (125 MHz, CDCl3): δ = 195.0 (C⚌O), 187.0 (C⚌O), 166.7 (C), 153.2 (CH), 163.2 (C), 138.0 (C), 137.2 (C), 131.7 (CH), 128.1 (CH), 130.5 (CH), 129.5 (C), 128.3 (CH), 120.3 (C), 121.6 (C), 121.5 (CH), 118.7 (CH), 112.8 (CH), 97.6 (CH) ppm. MS (70 eV) m/z = 360 (M+•, 100), 342, 286 (26), 239 (16), 212 (22). UV (EtOH): λmax(ɛ) = 416, 313, 234 nm. Anal. Calc. for C18H11Cl2NO3: C, 60.02; H, 3.08; N, 3.89. Found: C, 59.80; H, 3.04; N, 3.86%.

2.5.6

2.5.6 4,5-Difluoro-2-[2-(2(1H)quinolinylidene)acethyl]benzoic acid (2f, C18H11F2NO3)

Yield: 95%, mp: 224–227 °C. IR (KBr, cm−1): 3409, 1725, 1648, 1596, 1108 cm−1. 1H NMR (500 MHz, CDCl3): 1H NMR (500 MHz, CDCl3): δ = 15.5 (s, 1H, NH enaminone form), 11.6 (s, 1H, OH carboxylic acid), 8.4 (dd, 1H, 3J = 9.5, 4J = 6.2 Hz), 8.2 (d, 1H, 3J = 9.2 Hz), 7.7–7.8 (m, 2H), 7.4–7.5 (m, 3H), 7.2 (d, 1H, 3J = 9.2 Hz), 7.0 (s, 1H) ppm. 13C NMR (125 MHz, CDCl3): δ = 196.0 (C⚌O), 187.8 (C⚌O), 167.5 (CF), 164.3 (CF), 154.5 (C), 139.0 (C), 138.3 (C), 132.8 (CH), 129.6 (CH), 130.8 (CH), 129.9 (C), 129.4 (C), 123.0 (CH), 121.9 (CH), 121.2 (CH), 119.7 (CH), 112.2 (CH), 98.1 (CH) ppm. MS (70 eV) m/z = 327 (M+•, 100), 309, 253 (26), 206 (16), 179 (22). UV (EtOH): λmax(ɛ) = 413, 312, 232 nm. Anal. Calc. for C18H11F2NO3: C, 66.06; H, 3.39; N, 4.28. Found: C, 66.01; H, 3.36; N, 4.24%.

2.5.7

2.5.7 2,3,4,5-Tetrafluoro-6-[2-(2(1H)quinolinylidene)acethyl]benzoic acid (2g, C18H9F4NO3)

Yield: 97%, mp: 213–215 °C. IR (KBr, cm−1): 3411, 1729, 1648, 1595, 1110 cm−1. 1H NMR (500 MHz, CDCl3): δ = 15.6 (s, 1H, NH enaminone form), 11.8 (s, 1H, OH carboxylic acid), 8.2 (d, 1H, 3J = 9.3 Hz), 8.0 (dd, 1H, 3J = 8.2, 4J = 2.4 Hz), 7.7 (ddd, 3J = 8.4, 7.8, 4J = 2.4 Hz, 1H), 7.3–7.5 (m, 3H), 7.0 (s, 1H) ppm. 13C NMR (125 MHz, CDCl3): δ = 196.5 (C⚌O), 190.0 (C⚌O), 156.5 (CF), 144.0 (CF), 141.6 (C), 138.8 (CF), 137.0 (CF), 135.6 (C), 132.2 (CH), 129.9 (CH), 128.4 (CH), 124.8 (CH), 124.0 (C), 122.4 (C), 118.9 (CH), 118.2 (C), 116.0 (CH), 98.0 (CH) ppm. MS (70 eV) m/z = 363 (M+•, 100), 345, 289 (26), 242 (16), 215 (22). UV (EtOH): λmax(ɛ) = 413, 314, 235 nm. Anal. Calc. for C18H9F4NO2: C, 59.51; H, 2.50; N, 3.86. Found: C, 59.49; H, 2.48; N, 3.83%.

2.5.8

2.5.8 2,3,4,5-Tetrachloro-6-[2-(2(1H)quinolinylidene)acethyl]benzoic acid (2h, C18H9Cl4NO3)

Yield: 95%, mp: 223–225 °C. IR (KBr, cm−1): 3408, 1732, 1641, 1563, 1113 cm−1. 1H NMR (500 MHz, CDCl3): δ = 15.5 (s, 1H, NH enaminone form), 11.8 (s, 1H, OH carboxylic acid), 8.3 (d, 1H, 3J = 9.6 Hz), 7.9 (dd, 1H, 3J = 8.2, 4J = 2.2 Hz), 7.7 (ddd, 1H, 3J = 8.5, 7.8, 4J = 2.2 Hz), 7.3–7.4 (m, 3H), 7.1 (s, 1H) ppm. 13C NMR (125 MHz, CDCl3): δ = 194.0 (C⚌O), 186.8 (C⚌O), 154.5 (C), 142.0 (C), 140.3 (C), 137.3 (C), 135.8 (C), 132.6 (C), 130.2 (CH), 129.0 (CH), 127.4 (C), 124.0 (CH), 122.0 (C), 121.8 (C), 118.2 (CH), 117.8 (CH), 114.2 (CH), 97.5 (CH) ppm. MS (70 eV) m/z = 431 (M+•, 100), 433, 435 (26), 437 (16), 439 (22), 212, 170, 143. UV (EtOH): λmax(ɛ) = 415, 318, 235 nm. Anal. Calc. for C18H9Cl4NO3: C, 50.39; H, 2.11; N, 3.26. Found: C, 50.37; H, 2.9; N, 3.25%.

2.5.9

2.5.9 2,3,4,5-Tetrabromo-6-[2-(2(1H)quinolinylidene)acethyl]benzoic acid (2i, C18H9Br4NO3)

Yield: 91%, mp: 234–236 °C. IR (KBr, cm−1): 3409, 1727, 1642, 1592, 1104 cm−1. 1H NMR (500 MHz, CDCl3): δ = 15.3 (s, 1H, NH enaminone form), 11.9 (s, 1H, OH carboxylic acid), 8.1 (d, 1H, 3J = 9.3 Hz), 7.9 (dd, 1H, 3J = 8.4, 4J = 2.1 Hz), 7.6 (ddd, 3J = 8.6, 7.8, 4J = 2.1 Hz, 1H), 7.2–7.4 (m, 3H), 6.9 (s, 1H) ppm. 13C NMR (125 MHz, CDCl3): δ = 195.0 (C⚌O), 186.9 (C⚌O), 153.2 (C), 141.1 (C), 140.0 (C), 136.8 (C), 135.1 (CH), 131.9 (CH), 129.7 (CH), 129.0 (C), 126.4 (C), 124.5 (C), 122.2 (C), 121.8 (C), 117.2 (CH), 116.2 (CH), 114.5 (CH), 95.5 (CH) ppm. MS (70 eV) m/z = 603 (M+•, 100), 605, 607 (26), 608 (16), 610 (22), 558, 143. UV (EtOH): λmax(ɛ) = 415, 318, 235 nm. Anal. Calc. for C18H9Br4NO3: C, 35.62; H, 1.49; N, 2.31. Found: C, 35.50; H, 1.42; N, 2.2%.

3

3 Results and discussion

The poor thermal stability of isobenzofuranone limits the application of heat and strong acidic media, therefore, we decided to use SSA/wet SiO2 and microwave irradiation. Efficiency of the reaction is mainly affected by the amount of catalyst, temperature and presence of wet SiO2. As it is compiled in Table 1, the best results have been obtained at 100 °C with a amount of 0.1 g SSA in terms of yield. The increasing in the quantity of SSA up to 0.4 g not only increases the yield but results clearly indicate that even 0.1 g of SSA is sufficient to the hydrolysis of the isobenzofuranone. It is important to note that in the absence of wet SiO2 the reaction yield is decreased to zero even at 100 °C after 24 h. Also increasing the quantity of wet SiO2 was found to be not effective in the reaction yields and time.

Table 1 Optimization of the hydrolysis of isobenzofuranone under classical heating conditions.
Experimental number Catalyst (g) Time (h) Temperature (°C) Yielda (%)
1 0 1 100 16
2 0.1 1 60 20
3 0.1 1 80 45
4 0.1 1 100 58
5 0.1 1 120 56
6 0.1 1 150 49
7 0.2 1 100 40
8 0.4 1 130 34
Isolated yield.

The successful results of silica sulfuric acid catalyzed hydrolysis of various isobenzofuranone under solvent-free classical heating conditions and using microwave irradiation in presence of wet SiO2 are given in Table 3. In a typical experiment, a mixture of isobenzofuranone derivatives (1a–i, 1 mmol) and silica sulfuric acid (0.1 g) and wet SiO2 was stirred for 50–80 min under conventional heating conditions at 100 °C and using microwave irradiation for 5–20 min. The results clearly show that microwave irradiation improves the hydrolysis of isobenzofuranone derivatives and gives yields higher than those from conventional experiments. Experiment was conducted to study the hydrolysis of 1a under the optimized conditions obtained in the absence of silica sulfuric acid. The yield of product 2a was only 16%, while reaction occurred with wet SiO2 even after 24 h. To explore the generality of this work, we repeat this method for the hydrolysis of some carboxylic acid esters. It is noteworthy that not only aromatic carboxylic acid esters but also aliphatic carboxylic acid esters were smoothly hydrolyzed under the given conditions (Table 2).

Table 2 Hydrolysis of various carboxylic acid esters catalyzed by silica sulfuric acid under microwave irradiation.a
Entry Ester Yield (%) time (min)
Δ MW
1 80 (70) 94 (10)
2 75 (85) 93 (15)
3 80 (75) 98 (15)
4 75 (40) 94 (7)
5 75 (55) 94 (8)
6 85 (95) 99 (15)
7 75 (45) 94 (10)
8 80 (60) 93 (10)
9 75 (100) 92 (9)
10 80 (95) 93 (10)
All products were characterized by comparison of their melting or boiling points, IR, and 1H NMR spectra with those of authentic samples.

We believe that the presence of wet SiO2 provides an effective surface area for in situ generation of H2SO4. As indicated in Table 3, we have repeated the reaction numerous times with good success each time. In fact, we observed that the catalyst can be recycled and reused at least four times (Table 3, entry 2b).

The structures of products 1(a–i) were deducted by 1H and 13C NMR spectroscopy, mass spectrometry FT-IR and elemental analysis. The mass spectrum of 1a displayed the molecular ion (M+) peak at m/z 291, which was consistent with the adduct structure.

The 1H NMR spectrum of 2a exhibited two broad singlet, arising from the NH group (δ 15–16 ppm) and OH carboxylic acid (δ 11–12 ppm). Also one sharp singlet related to ⚌CH (δ 5.83 ppm). In IR spectra, the presence of absorption band at 1726 cm−1 due to C⚌O related to the carboxylic acid and signal at 3410 cm−1 due to O–H related to the hydroxyl group of the carboxylic acid. We conclude that the compounds are rather in the enaminone form (Gnichtel and Moller, 1981; Case and Schilt, 1979). In CDCl3 as solvent the structure of (B) is major (Scheme 2).

Tautomeric form of 2-ketomethylquinoline derivatives.
Scheme 2
Tautomeric form of 2-ketomethylquinoline derivatives.

4

4 Conclusion

In conclusion, from our experimental results it is evident that the solvent-free reaction using microwave irradiation proceeds with significant decrease in reactions times and comparably high chemical yields and purity, without involvement of toxic solvents, formation of any undesirable side products and epimerization toward classical heating conditions. Replacement of liquid acids with solid acid is all among desirable factors for the chemical industry which we have considered in our green chemistry approach. Moreover, a new feature here is the fact that the reaction is heterogeneous. We believe that the present methodology would be an important addition to existing methodologies.

Acknowledgment

We gratefully acknowledge the financial support from the research council of University of Kashan.

References

  1. , , , , . Synth. Commun.. 2002;32:3565-3572.
  2. , , , , . Inorg. Chim. Acta. 2005;358:77-83.
  3. , , , , , . Synlett 1995:1259-1262.
  4. , , . J. Heterocycl. Chem.. 1979;16:1135-1140.
  5. , , . Chem. Ber.. 1904;37:3011-3014.
  6. , , , , . Tetrahedron. 2007;63:3762-3769.
  7. , , . Liebiegs Ann. Chem. 1981:1751-1756.
  8. , , , , , . J. Mol. Catal. A: Chem.. 2004;210:23-28.
  9. , , , , . Bull. Korean Chem. Soc.. 2004;25:865-869.
  10. , , , , , . Tetrahedron Lett.. 1996;37:513-519.
  11. , , , , , . J. Mol. Catal. A: Chem.. 2007;270:236-240.
  12. , , , , . J. Braz. Chem. Soc.. 2004;15:773-782.
  13. , , . Chem. Rev.. 2002;102:3495-3502.
  14. , , , . Tetrahedron. 2000;56:3625-3629.
  15. , , , . Tetrahedron Lett.. 2005;46:2075-2083.
  16. , , , , . Tetrahedron Lett.. 2007;48:8230-8235.
  17. , . Green Chem.. 1999;1:43-55.
  18. , , . Tetrahedron Lett.. 1997;38:2043-2044.
  19. , , . Tetrahedron Lett.. 1997;38:7973-7976.
  20. , , . Tetrahedron Lett.. 1997;38:2621-2923.
  21. , , . Tetrahedron Lett.. 1997;38:4337-4338.
  22. , , , . Tetrahedron Lett.. 1993;34:4603-4606.
  23. , , , . Tetrahedron Lett.. 1993;34:3207-3210.
  24. , , , . Tetrahedron Lett.. 1993;34:3029-3032.
  25. , , , . Tetrahedron Lett.. 1997;38:7823-7824.
  26. , , , . Tetrahedron Lett.. 1997;38:6525-6528.
  27. , , , , . Tetrahedron Lett.. 2006;47:4921-4926.
  28. , , , , . Synlett 2003:1877-1883.
  29. , , , , , . Phosphor. Sulfur Silicon Relat. Elem.. 2004;179:2177-2183.
  30. , , , , . Synlett 2005:761-767.
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