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Synlett 2010(13): 2002-2008  
DOI: 10.1055/s-0030-1258128
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© Georg Thieme Verlag Stuttgart ˙ New York

Magnetically Recoverable Iron Nanoparticle Catalyzed Cross-Dehydrogena­tive Coupling (CDC) between Two Csp³-H Bonds Using Molecular Oxygen

Tieqiang Zenga,b, Gonghua Song*b, Audrey Mooresa, Chao-Jun Li*a
a Department of Chemistry, McGill University, 801 Sherbrooke St. West, Montreal, QC, H3A 2K6, Canada
Fax: +1(514)3983797; e-Mail: cj.li@mcgill.ca;
b Shanghai Key Laboratory of Chemical Biology, Institute of Pesticides and Pharmaceuticals, East China University of Science and Technology, Shanghai 200237, P. R. of China
Fax: +86(21)64252603; e-Mail: ghsong@ecust.edu.cn;
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Publication History

Received 19 April 2010
Publication Date:
09 July 2010 (online)

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Abstract

The oxidative C-C bond formations between Csp³-H bond adjacent to nitrogen and Csp³-H bond of nitroalkanes are catalyzed efficiently by magnetically recoverable iron nanoparticles using oxygen. The catalyst can be magnetically removed and recycled easily for nine times without decreasing activity.

Key words

iron nanoparticles - oxygen - cross-coupling - C-C bond formation

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The leaching of Fe residue in the resulting crude material was detected by Thermo Jarrell Ash ICP-AES. No obvious Fe leaching was detected (below detecting limit).

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Experimental Procedure
Fe3O4 [<50 nm particle size (TEM)], Fe2O3 (<50 nm particle size) and other reagents were purchased from Sigma-Aldrich and used without further purification. 2-Aryl-1,2,3,4-tetrahydroisoquinolines were prepared by the literature method.¹6 To a reaction tube charged with a magnetic stir bar and Fe3O4 nanoparticles (0.02 mmol, 10 mol%), 1,2,3,4-tetrahydroisoquinoline derivatives (0.2 mmol), and nitroalkane or acetone (0.5 mL) were added. Then the tube was filled up with molecular oxygen and stoppered. The reaction mixture was stirred at 100 ˚C (temperature of oil bath) for 24 h. The Fe3O4 nanoparticles were adsorbed on the magnetic stirring bar when the stirring was stopped. After cooled to r.t., the reaction solution was filtered through Celite in a pipette eluting with EtOAc. The volatile was removed in vacuo, and the residue was purified by column chromatography on silica gel (eluent: hexane-EtOAc = 5:1) to give the corresponding product. Fe3O4 nanoparticles were washed with EtOAc, air-dried, and used directly for the next round of reaction without further purification.
2-(3-Methoxyphenyl)-1,2,3,4-tetrahydroisoquinoline (1e) White solid. Isolated by flash column chromatography (hexane-EtOAc = 5:1, R f  = 0.7). ¹H NMR (400 MHz): δ = 7.26-7.15 (m, 5 H), 6.62-6.60 (m, 1 H), 6.53-6.52 (m, 1 H), 6.41-6.39 (m, 1 H), 4.42 (s, 2 H), 3.82 (s, 3 H), 3.57 (t, J = 5.6 Hz, 2 H), 2.99 (t, J = 6.0 Hz, 2 H) ppm. ¹³C NMR (100 MHz): δ = 160.8, 151.9. 134.9, 134.5, 130.0, 128.5, 126.6, 126.4, 126.1, 108.0, 103.3, 101.5, 55.2, 50.6, 46.4, 29.2 ppm. HRMS (APCI): m/z calcd for C16H18NO [M + 1]+: 240.1383; found: 240.1381.
2-(3-Methoxyphenyl)-1-(nitromethyl)-1,2,3,4-tetrahydroisoquinoline (3i) Isolated by flash column chromatography (hexane-EtOAc = 5:1, R f  = 0.4). Light yellow oil. ¹H NMR (400 MHz): δ = 7.28-7.17 (m, 4 H), 7.14-7.12 (m, 1 H), 6.60 (dd, J = 8.4, 2.4 Hz, 1 H), 6.54 (m, 1 H), 6.42 (dd, J = 8.0, 2.0 Hz, 1 H), 5.54 (dd, J = 7.2, 6.8 Hz, 1 H), 4.87 (dd, J = 12.0, 7.2 Hz, 1 H), 4.55 (dd, J = 11.6, 6.8 Hz, 1 H), 3.80 (s, 3 H), 3.66-3.58 (m, 2 H), 3.00 (ddd, J = 16.4, 8.8, 6.4 Hz, 1 H), 2.68 (dt, J = 16.4, 5.2 Hz, 1 H) ppm. ¹³C NMR (100 MHz): δ = 160.9, 149.7, 135.2, 132.9, 130.2, 129.2, 128.2, 127.0, 126.7, 107.5, 104.0, 101.4, 78.8, 58.3, 55.2, 42.1, 26.6 ppm. HRMS (APCI): m/z calcd for C17H19N2O3 [M + 1]+: 299.1390; found: 299.1391.
2-(3-Methoxyphenyl)-1-(1-nitroethyl)-1,2,3,4-tetrahydroisoquinoline (3j) The ratio of isolated diastereomers is 1.7. Isolated by flash column chromatography (hexane-EtOAc = 5:1, R f  = 0.4). Light yellow oil.
Major isomer: ¹H NMR (400 MHz): δ = 5.05 (dq, J = 14.8, 6.4 Hz, 1 H), 3.79 (s, 3 H), 1.55 (d, J = 6.4 Hz, 3 H) ppm. ¹³C NMR (100 MHz): δ = 160.7, 150.2, 134.7, 131.9, 130.0, 128.7, 128.2, 126.6, 107.9, 104.0, 101.8, 85.4, 62.8, 55.2, 42.7, 26.5, 16.3 ppm.
Minor isomer: ¹H NMR (400 MHz): δ = 4.88 (dq, J = 14.8, 6.4 Hz, 1 H), 3.82 (s, 3 H), 1.71 (d, J = 6.8 Hz, 3 H) ppm. ¹³C NMR (100 MHz): δ = 160.8, 150.5, 135.6, 133.8, 130.1, 129.1, 128.3, 127.3, 107.2, 103.1, 101.1, 88.9, 61.2, 55.2, 43.5, 26.9, 17.5 ppm.
Other overlapped peaks: ¹H NMR (400 MHz): δ = 7.27-7.08 (m), 7.01-7.00 (m), 6.62-6.52 (m), 6.40-6.37 (m), 5.25-5.24 (m), 3.85-3.83 (m), 3.58-3.52 (m), 3.52-3.04 (m), 2.96-2.86 (m) ppm. ¹³C NMR (100 MHz): δ = 126.2 ppm. HRMS (APCI): m/z calcd for C18H21N2O3 [M + 1]+: 313.1547; found: 313.1549.
2-(3-Methoxyphenyl)-1-(1-nitropropyl)-1,2,3,4-tetrahydroisoquinoline (3k) The ratio of isolated diastereomers is 1.6. Isolated by flash column chromatography (hexane-EtOAc = 5:1, R f  = 0.4). Light yellow oil.
Major isomer: ¹H NMR (400 MHz): δ = 5.12 (d, J = 9.6 Hz, 1 H), 4.86 (m, 1 H), 3.77 (s, 3 H) ppm. ¹³C NMR (100 MHz): δ = 160.5, 150.3, 135.5, 133.8, 130.1, 129.3, 128.5, 128.2, 125.9, 108.3, 103.9, 102.2, 92.9, 62.2, 55.2, 42.3, 25.8, 24.5 ppm.
Minor isomer: ¹H NMR (400 MHz): δ = 5.22 (d, J = 9.2 Hz, 1 H), 4.67 (m, 1 H), 3.81 (s, 3 H) ppm. ¹³C NMR (100 MHz): δ = 160.7, 150.3, 134.6, 132.1, 129.8, 128.6, 128.2, 127.2, 126.6, 106.8, 102.8, 100.8, 96.1, 60.7, 55.1, 43.5, 26.9, 25.0 ppm.
Other overlapped peaks: ¹H NMR (400 MHz): δ = 7.26-7.08 (m), 7.01-7.18 (m), 7.00-6.98 (m), 6.62-6.52 (m), 6.40-6.35 (m), 3.87-3.47 (m), 3.12-3.06 (m), 2.93-2.85 (m), 2.26-2.06 (m), 1.86-1.78 (m), 0.96-0.92 (m) ppm. ¹³C NMR (100 MHz): δ = 10.6 ppm. HRMS (APCI): m/z calcd for C19H23N2O3 [M + 1]+: 327.1703; found: 327.1703.