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Synlett 2008(12): 1777-1780  
DOI: 10.1055/s-2008-1078565
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Copper-Free Sonogashira Reaction Using Gold Nanoparticles Supported on Ce2O3, Nb2O5 and SiO2 under Microwave Irradiation

Rodrigo O. M. A. de Souzaa, Mariana S. Bittara, Laiza V. P. Mendesa, Carla Michele F. da Silvaa, Victor Teixeira da Silvab, O. A. C. Antunes*a
a Instituto de Química, CT Bl. A 641, Cidade Universitária, Rio de Janeiro, RJ 21941-909, Brazil
Fax: +55(21)25627559; e-Mail: octavio@iq.ufrj.br;
b NUCAT/PEQ/COPPE/UFRJ, CT Bl. G, Cidade Universitária, Rio de Janeiro, RJ 21941-909, Brazil
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Publication History

Received 1 February 2008
Publication Date:
02 July 2008 (online)

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Abstract

In the present communication we wish to report a copper-free Sonogashira reaction catalyzed by gold-supported catalysts under microwave irradiation. Aryl and alkyl acetylenes were used and good yields were obtained with short reaction times when DMF was used as solvent. Three different supported gold catalysts were used and Au/SiO2 gave the best result for both aryl and alkyl acetylenes.

Key words

Sonogashira reaction - gold nanoparticles - supported catalyst

10

A mixture of the aryl halide (1.00 mmol), Au-supported catalyst (3 mol%), phenylacetylene or 1-octyne (1.00 mmol) and K2CO3 (138 mg, 1.00 mmol) was mixed in DMF (5.0 mL). Microwave-assisted syntheses were conducted with a CEM Discover focussed microwave oven (150 W). After the reaction, usual aqueous workup and column chromatograph-ic purification process on silica gel (hexanes-EtOAc, 9:1) were carried out. The spectroscopic data of compounds 3, 8, 9, 13, 14 and 15 are as follows.
Compound 3: ¹H NMR (300 MHz, CDCl3): δ = 7.45-7.50 (m, 4 H), 7.20-7.25 (m, 6 H).
Compound 8: ¹H NMR (300 MHz, CDCl3): δ = 8.10 (m, 2 H), 7.95 (m, 2 H), 7.49-7.53 (m, 2 H), 7.20-7.25 (m, 3 H).
Compound 9: ¹H NMR (300 MHz, CDCl3): δ = 7.51 (m, 2 H), 7.46 (m, 2 H), 7.18-7.23 (m, 3 H), 6.84 (m, 2 H), 3.80 (s, 3 H).
Compound 13: ¹H NMR (300 MHz, CDCl3): δ = 7.25 (m, 1 H), 7.13 (m, 4 H), 2.38 (m, 2 H), 1.40 (m, 8 H), 0.89 (m, 3 H).
Compound 14: ¹H NMR (300 MHz, CDCl3): δ = 8.10 (m, 2 H), 7.89 (m, 2 H), 2.35 (m, 2 H), 1.33 (m, 8 H), 0.85 (m, 3 H).
Compound 15: ¹H NMR (300 MHz, CDCl3): δ = 7.36 (m, 2 H), 6.79 (m, 2 H), 3.55 (s, 3 H), 2.40 (m, 2 H), 1.45 (m, 8 H), 1.11 (m, 3 H).
Commercial Nb2O5 (49 m²/g¹) and SiO2 (200 m²/g), kindly provided by CBMM and DEGUSA, were used as received. CeO2 (20m²/g) was obtained by calcination of Ce(III) nitrate hexahydrate (ACROS, 99.5%) at 800 ˚C/h in a conventional oven. Gold was incorporated into the supports using the deposition-precipitation method at a constant pH of 8 by addition of Na2CO3 and using a HAuCl4 (ACROS) solution as gold source. Characterization of the catalysts by small-angle X-ray scattering (SAXS) revealed gold particle sizes of 4.9, 5.9 and 4.2 nm for Nb2O5, CeO2 and SiO2 supports, respectively.