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Rapid, efficient and eco-friendly procedure for the synthesis of quinoxalines under solvent-free conditions using sulfated polyborate as a recyclable catalyst

KRISHNA S INDALKAR, CHETAN K KHATRI and GANESH U CHATURBHUJ*

Department of Pharmaceutical Sciences and Technology, Institute of Chemical Technology, Mumbai, Maharashtra 400 019, India

Email: gu.chaturbhuj@gmail.com *For Correspondence

Table of Contents

Page

1. Experimental S2

1.1. Materials and methods

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1.2. Preparation of sulfated polyborate catalyst S2

1.3. General procedure for the synthesis of quinoxaline derivatives

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2. Spectral data of synthesized compounds S4

3. Copies of 1HNMR and 13C NMR spectra of synthesized compounds S5

4. References S11

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1. Experimental

1.1 Materials and methods:

Melting points of all the compounds were recorded by AnalabThermoCal melting point

apparatus in the open capillary tube and are uncorrected. The FTIR spectra (KBr) were

recorded on Shimadzu FTIRAffinity-1 Fourier Transform Infrared spectrophotometer. 1H

NMR spectra were recorded on MR400 Agilent Technology NMR spectrometer using

tetramethylsilane (TMS) as an internal standard and DMSO-d6/CDCl3 as solvent. X-ray

diffractograms (XRD) were recorded on Rigakuminiflex X-ray Diffractometer. The SEM-

EDAX characterization was performed on a JEOL JSM-638DLA scanning electron

microscope equipped with energy dispersive X-ray spectrometer. The potentiometric analysis

was performed on ElicoLI 120 pH meter. Chemicals and solvents used were of LR grade and

purchased from SD fine, Avra Synthesis and Spectrochem and used without purification. The

purity determination of the starting materials and reaction monitoring was accomplished by

thin-layer chromatography (TLC) on Merck silica gel G F254 plates. All the products are

known compounds and were identified by 1H NMR spectroscopy.

1.2 Preparation of sulfated polyborate catalyst:

Boric acid was heated in a petri dish at 200 °C for 4h to convert it to the polyboric acid;

resultant glassy solid was then ground into fine powder. Polyboric acid powder (5 g) was

suspended in chloroform (20 ml) in 250 ml round bottom flask, then chlorosulfonic acid (4.23

ml) was added dropwise over a period of 30 minutes at room temperature. The mixture was

further stirred for 120 min. The reaction was quenched by adding ethanol (10 ml). Residual

HCl gas was flushed with nitrogen, the solid was filtered, washed several times with

chloroform. Finally, solid sulfated polyborate was dried at 100 °C in hot air oven till constant

weight.The catalyst was characterized by various analytical techniques such as

potentiometric analysis, Fourier transform infrared spectroscopy (FTIR), X-ray

diffraction (XRD), and scanning electron microscopy (SEM) energy dispersive X-ray

spectroscopy (EDAX).

1.3General procedure for the synthesis of quinoxaline derivatives

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To a mixture of substituted o-phenylenediamines derivative (2.0 mmol) and 1,2-

diketone / α-hydroxy ketone (2.0 mmol) was added sulfated polyborate (10 wt %).

The reaction mixture was stirred at 100 °C in an oil bath. The reaction was monitored

by thin layer chromatography (TLC). After completion of the reaction, the mixture

was cooled to room temperature and quenched by water. The resultant product was

filtered/extracted with EtOAc to get the product. Crude products either

recrystallizedfrom ethanol or purified by column chromatography using silica as

stationary phase and EtOAc: pet. ether solvent system. The products obtained were

known compounds and were identified by melting point and 1H NMR spectroscopy.

The spectral data were compared with the literature values.

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2. Spectral data of synthesized compounds:

1. 2,3-diphenylquinoxaline (Table 3, entry 1):1,2

White solid, 1H NMR (400 MHz, CDCl3): δ 8.18- 8.16 (m, 2H), 7.78- 7.76 (m, 2H), 7.52-7.50 (m, 4H), 7.34-7.31 (m, 6H).13C NMR (101MHz, CDCl3): δ 153.44, 141.20, 139.05, 129.92, 129.80, 129.18, 128.77, 128.24.

2. 5-methyl-2,3-diphenylquinoxaline (Table 3, entry 2): 2,3

White solid, 1H NMR (400 MHz, CDCl3): δ 8.00 (d, J= 8 Hz, 1H), 7.66-7.51(m, 6H), 7.34- 7.25 (m, 6H), 2.85 (s, 3H).13C NMR (101MHz, CDCl3): δ 152.78, 151.72, 141.11, 140.35, 139.37, 139.32, 137.58, 130.10, 129.76, 129.64, 128.64, 128.25, 128.06, 126.91, 17.10.

3. 6-chloro-2,3-diphenylquinoxaline (Table 3, entry 5):2,3

White solid, 1H NMR (400 MHz, CDCl3): δ 8.16 (s, 1H), 8.10 (d, J= 8 Hz, 1H), 7.70 (d, J = 8 Hz1H), 7.51-7.49 (m, 4H), 7.37-7.31(m, 6H).13C NMR (101MHz, CDCl3): δ 154.25, 153.58, 141.44, 139.68, 138.68, 138.61, 135.62, 130.92, 130.39, 129.80, 129.75, 129.07, 128.98, 128.28, 128.04.

4. 6-nitro-2,3-diphenylquinoxaline (Table 3, entry 6):1

Light yellow solid, 1H NMR (400 MHz, CDCl3): δ 9.07 (s, 1H), 8.53 (d, J = 8 Hz, 1H), 8.29 (d, J = 8 Hz, 1H), 7.57-7.54 (m, 4H), 7.42- 7.35 (m, 6H).

5. 2,3-dimethylquinoxaline (Table 3, entry 7):3,4

Light yellow solid, 1H NMR (400 MHz, CDCl3): δ 7.97-7.94(m, 2H), 7.65-7.63 (m, 2H), 2.71 (s, 6H).13C NMR (101MHz, CDCl3): δ 153.42, 141.04, 128.77, 128.27, 23.16.

6. Quinoxaline (Table 3, entry 13)5

Brown Solid, 1H NMR (400 MHz, CDCl3): δ 8.85 (s, 2H), 8.12-8.10 (m, 2H), 7.79-7.77(m, 2H).

7. 6-chloroquinoxaline (Table 3, entry 17):6

Brown Solid, 1H NMR (400 MHz, CDCl3):δ 8.84 (d, J = 4.4 Hz, 2H), 8.10 (s, 1H), 8.04 (d, J = 8 Hz1H), 7.72 (d, J = 8 Hz, 1H).

8. 6-butylquinoxaline (Table 3, entry 18):

Brown liquid, 1H NMR (400 MHz, CDCl3):δ 8.78 (d, J = 8 Hz, 2H), 8.00 (d, J = 12 Hz, 1H), 7.87(s, 1H), 7.62(d, J = 8 Hz, 1H), 2.89(t, J = 8 Hz, 2H), 1.75-1.68 (m, 2H), 1.43-1.37 (m, 2H), 0.94 (t, J = 8 Hz,3H).

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13C NMR (101MHz, CDCl3): δ 145.47, 144.80, 144.06, 143.10, 141.67, 131.73, 129.00, 127.60, 35.67, 33.06, 22.25, 13.87.

3. Copies of 1HNMR and 13C NMR spectra of synthesized compounds:

1. 2,3-diphenylquinoxaline (Table 3, entry 1):

13C NMR (101 MHz, CDCl3)

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2. 5-methyl-2,3-diphenylquinoxaline (Table 3, entry 2):

13C NMR (101 MHz, CDCl3)

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3. 6-chloro-2,3-diphenylquinoxaline (Table 3, entry 5):

13C NMR (101 MHz, CDCl3)

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4. 6-nitro-2,3-diphenylquinoxaline (Table 3, entry 6):

5. 2,3-dimethylquinoxaline (Table 3, entry 7):

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13C NMR (101 MHz, CDCl3)

6. Quinoxaline (Table 3, entry 13):

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7. 6-chloroquinoxaline (Table 3, entry 17):

8. 6-butylquinoxaline (Table 3, entry 18)

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13C NMR (101 MHz, CDCl3)

5. References

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1. Kadam H K, Khan S, Kunkalkar R A and Tilve S G 2013 Graphite catalyzed green synthesis of

quinoxalines Tetrahedron Lett. 54 1003

2. Zhang X Z, Wang J X, Sun Y J and Zhan H W 2010 Synthesis of quinoxaline derivatives catalyzed

by PEG-400 Chin. Chem. Lett. 21 395

3. Go A, Lee G, Kim J, Bae S, Lee B M and Kim B H 2015 One-pot synthesis of quinoxalines from

reductive coupling of 2-nitroanilines and 1,2-diketones using indium Tetrahedron 71 1215

4. Paul S and Basu B 2011 Synthesis of libraries of quinoxalines through eco-friendly tandem

oxidation–condensation or condensation reactions Tetrahedron Lett. 52 6597

5. Zhou W, Taboonpong p, Aboo A, Zhang L, Jiang J and Xiao J 2016 A convenient procedure for the

oxidative dehydrogenation of n-heterocycles catalyzed by FeCl2/DMSO Synlett 27 1806

6. Chambers R, Parsons M, Sandford G, Skinner C, Atherton M and Moilliet J 1999 Elemental

fluorine. Part 10.1 Selective fluorination of pyridine,quinoline and quinoxaline derivatives with

fluorine–iodine mixtures J. Chem. Soc. Perkin Trans. 1 803

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