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Synlett 2007(10): 1581-1584  
DOI: 10.1055/s-2007-980365
LETTER
© Georg Thieme Verlag Stuttgart · New York

Copper-Nanoparticle-Catalyzed A3 Coupling via C-H Activation

Mazaahir Kidwai*a, Vikas Bansala, Neeraj Kumar Mishraa, Ajeet Kumarb, Subho Mozumdarb
a Green Chemistry Research Laboratory, Department of Chemistry, University of Delhi, Delhi 110007, India
b Laboratory of Nanobiotechnology, Department of Chemistry, University of Delhi, Delhi 110007, India
Fax: +91(11)27666235; e-Mail: kidwai.chemistry@gmail.com;
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Publication History

Received 17 March 2007
Publication Date:
06 June 2007 (online)

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Abstract

Recyclable metal nanoparticles provide an efficient, economic, and novel route for the synthesis of propargylamines via three-component A3 coupling reaction of aromatic aldehyde, amine and alkyne. This method provides a wide range of substrate applicability. This protocol avoids the use of heavy metal, co-catalyst and gives propargylamines in quantitative yield.

Key words

metal nanoparticles - propargylamines - heterogeneous catalysis - cyclic secondary amines - one-pot multicomponent reaction

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Preparation of Cu Nanoparticles: A chemical method involving the reduction of Cu2+ ions to Cu(0) in a reverse micellar system was employed to prepare the Cu nanoparticles. Poly(oxyethylene)(tetramethyl)phenyl ether, commercially known as Triton X-100 (TX-100) was used as surfactant in the process. To a reverse micellar solution of CuSO4 (aq), another reverse micellar solution of N2H2 (aq) was added with constant stirring. In the presence of N2 atmosphere the resulting solution was further stirred for 3 h to allow the complete Oswald ripening (particle growth). The Cu nanoparticles were extracted using anhyd EtOH followed by centrifugation. By varying the H2O content parameter Wo (defined as the molar ratio of water to surfactant concentration, Wo = [H2O]/[surfactant]) the size of nanoparticles could be controlled. The nanoparticles prepared were spherical in shape, with an average size of 18 ± 2 nm as confirmed by TEM photograph and QELS data. The metallic nature of the Cu(0) nanoparticles was confirmed by a characteristic UV absorption of the particles dispersed in cyclohexane (580 nm).
Typical Procedure A 50-mL round-bottomed flask was charged with aromatic or heterocylic aldehydes 1a-h (1 mmol), secondary amine (1 mmol) and phenylacetylene (1.5 mmol) in MeCN (5 mL) and the contents of the flask were stirred under a nitrogen atmosphere followed by the addition of Cu nanoparticles (15 mol%, 18 ± 2 nm). The resulting solution was refluxed at 100-110 °C for the appropriate time mentioned in Table [4] . The extent of reaction was monitored by TLC. After completion of the reaction, the reaction mixture was centrifuged at 2000-3000 rpm, at 10 °C for 5 min. The organic layer was decanted and the remaining Cu nanoparticles were reused for further reactions. The organic layer was dried over anhyd Na2SO4 and the solvent was removed in vacuo. The crude product was subjected to purification by silica gel column chromatography using a mixture of 15% EtOAc, 5% MeOH and 80% PE as eluent to yield the propargylamine 3a-h. The structures of all the products were unambiguously established on the basis of their spectral analysis (IR, 1H NMR, 13C NMR and GC-MS data). All the products are known compounds.