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Synlett 2008(6): 886-888  
DOI: 10.1055/s-2008-1042897
LETTER
© Georg Thieme Verlag Stuttgart · New York

Copper-Catalyzed, Palladium-Free Carbonylative Sonogashira Coupling Reaction of Aliphatic and Aromatic Alkynes with Iodoaryls

Pawan J. Tambade, Yogesh P. Patil, Nitin S. Nandurkar, Bhalchandra M. Bhanage*
Department of Chemistry, Institute of Chemical Technology (Autonomous), University of Mumbai, N. Parekh Marg, Matunga, Mumbai 400 019, India
Fax: +91(22)24145614; e-Mail: bhalchandra_bhanage@yahoo.com;
Further Information

Publication History

Received 1 November 2007
Publication Date:
11 March 2008 (online)

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Abstract

Copper bis(2,2,6,6-tetramethyl-3,5-heptanedionate) catalyzed carbonylative Sonogashira coupling reactions of aliphatic/aromatic alkynes with iodoaryls are reported for the first time. The protocol eliminates the use of a toxic, air-sensitive, and expensive Pd-phosphine-based catalytic system, and provides high yields of desired products.

Key words

Sonogashira - carbonylation - iodoaryls - alkynes - copper

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Typical Procedure for the Preparation of Cu(TMHD) 2
NaOH (22 mmol) was dissolved in MeOH (20 mL) with stirring and the resulting solution was cooled to r.t., followed by addition of TMHD (20 mmol). To the mixture, a solution obtained by dissolving Cu(NO3)2·6H2O (10 mmol) in MeOH (20 mL) was added over a period of 30 min. The reaction mixture was stirred for 6 h and the resulting precipitate was filtered and dried. Yield 93%, mp 196-198 °C.

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General Procedure To an 100 mL autoclave, phenylacetylene (3.0 mmol), iodobenzene (2.0 mmol), Cu(TMHD)2 (0.1 mmol), toluene (10 mL) and Et3N (6.0 mmol) were added. The mixture was first stirred for 10 min, then the vessel pressures 8-20 atm of CO and the reaction mixture was heated at 90 °C for 14 h. After the reaction was complete, the mixture was extracted with EtOAc (3 × 10 mL), the combined organic extracts were dried over Na2SO4, and the solvent was removed under vacuum. The residue obtained was purified by column chromatography (silica gel, 60-120 mesh) using PE (60:80)-EtOAc as eluent to afford the pure products. All the compounds are known and were characterized by GC-MS (Shimadzu) and NMR (Varian 300 MHz).
Spectroscopic Data of Representative Compounds
Table 2, Entry 1: GC-MS: m/z (%) = 206 [M+], 178, 129 (100). 1H NMR (300 MHz, CDCl3, 25 °C): δ = 7.49-7.54 (m, 5 H), 7.61-7.63 (m, 1 H), 7.68-7.70 (m, 2 H), 8.23 (ddd, J = 8.4, 2.1, 1.2, 2 H) ppm. 13C NMR (70 MHz, CDCl3, 25 °C): δ = 87.0, 93.2, 120.2, 128.8, 128.8, 129.2, 130.9, 133.2, 134.3, 137.0, 178.1 ppm.
Table 2, Entry 2: GC-MS: m/z (%) = 220 [M+], 192 (100), 165, 129. 1H NMR (300 MHz, CDCl3, 25 °C): δ = 2.44 (s, 3 H), 7.29-7.44 (m, 5 H), 7.67 (d, J = 8.4 Hz, 2 H), 8.11 (d, J = 8.4 Hz, 2 H) ppm. 13C NMR (70 MHz, CDCl3, 25 °C ):
δ = 21.9, 87.0, 92.7, 120.3, 128.8, 129.4, 129.9, 130.8, 133.1, 134.7, 145.3, 177.8 ppm.
Table 3, Entry 1: GC-MS: m/z (%) = 186 [M+], 105 (100), 77. 1H NMR (300 MHz, CDCl3, 25 °C): δ = 0.98 (t, J = 2.8, 4.8, 7.2, 3 H), 1.26-1.33 (m, 2 H), 1.63-1.69 (m, 2 H), 2.51 (t, J = 7.2, 6.8, 2 H), 7.460-7.59 (m, 3 H), 8.12-8.15 (m, 2 H) ppm. 13C NMR (70 MHz, CDCl3, 25 °C): δ = 13.7, 19.1, 22.7, 29.9, 80.0, 97.0, 128.6, 129.7, 131.8, 134.0, 178.1 ppm.