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Synlett 2008(19): 3063-3067  
DOI: 10.1055/s-0028-1087342
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Ligand-Free C-S Bond Formation Catalyzed by Copper(I) Oxide

Hua-Jian Xua, Xiao-Yang Zhaoa, Yao Fu*b, Yi-Si Feng*a
a School of Chemical Engineering, Hefei University of Technology, Hefei, 230009, P. R. of China
b Department of Chemistry, University of Science and Technology of China, Hefei 230026, P. R. of China
Fax: +86(551)3607476; e-Mail: fuyao@ustc.edu.cn;
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Received 9 August 2008
Publikationsdatum:
12. November 2008 (online)

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Abstract

An efficient ligand-free Cu2O-catalyzed C-S bond-formation reaction was developed. A large number of diaryl sulfides and alkylaryl sulfides could be rapidly assembled using this new reaction protocol.

Key words

copper(I) oxide - ligand-free - C-S coupling - iodides - thiols

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General Experimental Procedure
All reagents and solvents were pure analytical-grade materials purchased from commercial sources and were used without further purification. The ¹H NMR and ¹³C NMR spectra were recorded in CDCl3 on a 300 MHz instrument with TMS as internal standard. High-resolution mass spectra (HRMS) were determined on a Micromass GCT-MS mass spectrometer. Thin-layer chromatography was carried out with 0.2 mm thick SiO2 plates (GF254). The columns were hand packed with silica gel 60 (200-300). All reactions were carried out in a Schlenk tube equipped with a magnetic stir bar under Ar atmosphere. A Schlenk tube was charged with Cu2O (0.05 mmol), KOH (2 mmol) and solid substrate, if present. Then, liquid reagents (aryl or heteroaryl halide, 1 mmol; thiol, 1.1 mmol), solvent (1 mL) were added under Ar. The reaction vessel was closed and placed under stirring in a preheated oil bath at 80 ˚C. The reaction mixture was stirred for 24 h. The resulting suspension was cooled to r.t. and filtered through a pad of filter paper with the help of EtOAc (10 mL). The filtrate was concentrated and the residue was purified by silica gel chromatography.
(4-Methoxyphenyl)phenylsulfane (Entry 2, Table 1)
¹H NMR (300 MHz, CDCl3): δ = 3.78 (s, 3 H), 6.98 (d, J = 8.7 Hz, 2 H), 7.17-7.21 (m, 5 H), 7.40 (d, J = 9.0 Hz,
2 H) ppm. ¹³C NMR (75 MHz, CDCl3): δ = 55.2, 115.0, 124.2, 125.7, 128.2, 128.9, 135.3, 138.6, 159.8 ppm. HRMS: m/z calcd for C13H12OS: 216.0609; found: 216.0613.
Phenyl( p -tolyl)sulfane (entry 20, Table 1)
¹H NMR (300 MHz, CDCl3): δ = 2.31 (s, 3 H), 7.09-7.29 (m, 9 H) ppm. ¹³C NMR (75 MHz, CDCl3): δ = 21.1, 126.4, 129.0, 129.8, 130.1, 131.4, 132.3, 137.2, 137.5 ppm. HRMS: m/z calcd for C13H12S: 200.0660; found: 200.0652.

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No Cu was found in pure diphenylsulfane (entry 4, Table  [¹] ) with X-radial fluorescence-spectrum determining.