Synlett 2010(4): 610-614  
DOI: 10.1055/s-0029-1219151
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Copper(I) Halide Mediated Tandem 1,4-Aryl Migration-Oxidative Amidyl Radical Cyclisation of Bromosulfonamides

Andrew J. Clark*, David R. Fullaway, Nicholas P. Murphy, Hemal Parekh
Department of Chemistry, University of Warwick, Coventry, West Midlands, CV4 7AL, UK
Fax: +44(2476)524112; e-Mail: a.j.clark@warwick.ac.uk;
Further Information

Publication History

Received 8 October 2009
Publication Date:
22 December 2009 (online)

Abstract

Reaction of N-butyl-N-(2-bromo-2-methylpropionyl)-arylsulfonamides with CuBr/tripyridylamine leads to amidyl radicals via 1,4-aryl migration with concomitant loss of SO2, which can further undergo cyclisation to oxindoles or reduction to amides with the ratio dependent upon the temperature and solvent utilised.

    References and Notes

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14

2-Bromo-N-butyl-2-methyl-N-4-tolylpropanamide (1.50 g, 4.8 mmol) was added to anhyd AlCl3 (1.62 g, 12.1 mmol) under a stream of nitrogen. The mixture was heated at 50 ˚C for 10 min and then maintained at 160 ˚C for 1 h. The mixture was washed with H2O (5 × 50 mL) and extracted with Et2O, dried over MgSO4, and evaporated to give 16c (0.45 g, 41%) after chromatography (PE-EtOAc, 10:1); R f  = 0.40 (PE-EtOAc, 10:1). IR: νmax = 2962, 2929, 2865, 1705, 1619, 1599, 1493, 1381, 1351, 1192 cm. ¹H NMR (400 MHz, CDCl3): δ = 7.04 (1 H, d, J = 8.0 Hz), 7.03 (1 H, s), 6.75 (1 H, d, J = 8.0 Hz), 3.69 (2 H, t, J = 8.0 Hz), 2.34 (3 H, s), 1.65 (2 H, quin, J = 8.0 Hz), 1.35 (2 H, sext, J = 8.0 Hz), 1.35 (3 H, s), 0.94 (3 H, t, J = 8.0 Hz). ¹³C NMR (75.5 MHz, CDCl3): δ = 181.3, 139.7, 136.1, 131.7, 127.7, 123.3, 108.1, 44.1, 39.6, 29.5, 24.5, 21.1, 20.1, 13.8. ESI-HRMS: m/z calcd for Na+C15H21NO: 254.1515; found [Na+]: 254.1522.
Data for the Mixture of 8c and 19
IR: νmax = 2963, 2931, 2871, 1707, 1606, 1462, 1383, 1343, 1223 cm. ESI-HRMS: m/z calcd for Na+C15H21NO: 254.1515; found [Na+]: 254.1519.
Data for 19
¹H NMR (400 MHz, CDCl3): δ = 7.14 (1 H, t, J = 8.0 Hz), 6.81 (1 H, d, J = 8.0 Hz), 6.71 (1 H, d, J = 8.0 Hz), 3.70 (2 H, t, J = 8.0 Hz), 2.40 (3 H, s), 1.65 (2 H, quin, J = 8.0 Hz), 1.44 (3 H, s), 1.37 (2 H, sext, J = 8.0 Hz), 0.94 (3 H, t, J = 8.0 Hz). ¹³C NMR (75.5 MHz, CDCl3): δ = 181.3, 142.3, 134.2, 132.8, 127.4, 124.7, 106.1, 44.9, 39.6, 29.5, 22.4, 20.1, 18.2, 13.8.
Data for 8c
¹H NMR (400 MHz, CDCl3): δ = 7.08 (1 H, d, J = 8.0 Hz), 6.86 (1 H, d, J = 8.0 Hz), 6.68 (1 H, s), 3.69 (2 H, t, J = 8.0 Hz), 2.38 (3 H, s), 1.65 (2 H, quin, J = 8.0 Hz), 1.37 (2 H, sext, J = 8.0 Hz), 1.34 (3 H, s), 0.95 (3 H, t, J = 8.0 Hz). ¹³C NMR (75.5 MHz, CDCl3): δ = 181.3, 142.3, 137.6, 133.2, 122.6, 122.1, 109.2, 43.8, 39.5, 29.6, 24.6, 21.8, 20.1, 13.8.

15

A typical procedure is illustrated for reaction of 1b with CuBr (entry 2, Table  [¹] ). Substrate 1b (0.3 mmol) was added to dry CH2Cl2 (2 mL), and CuBr (0.33 mmol) and tripyridylamine (0.33 mmol) were added. The reaction mixture was heated at 40 ˚C for 18 h. Upon cooling, the crude mixture was passed through a small silica plug (eluting with EtOAc, 20 mL to remove copper residues). After evaporation of the solvent and chromatography (PE-EtOAc, 8:1) a mixture of amide 3b and oxindole 8b were isolated in the ratio of 1.4:1.0, combined yield 78%. Spectroscopic data for 3b were identical to an authentic sample prepared previously²,9 and data for 8b were identical to that reported above.¹4