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Synlett 2008(11): 1657-1660  
DOI: 10.1055/s-2008-1077873
LETTER
© Georg Thieme Verlag Stuttgart · New York

Efficient Sonogashira Coupling Reaction Catalyzed by Palladium(II) β-Oxoiminatophosphane Complexes under Mild Conditions

Dong-Hwan Lee, Huili Qiu, Min-Ho Cho, Ik-Mo Lee, Myung-Jong Jin*
Department of Chemical Engineering and Chemistry, Inha University, Incheon 402-751, Korea
Fax: +82(32)8720959; e-Mail: mjjin@inha.ac.kr;
Further Information

Publication History

Received 26 March 2008
Publication Date:
11 June 2008 (online)

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Abstract

Palladium(II) β-oxoiminatophosphane complexes were used as catalysts for the Sonogashira coupling reaction. In the presence of very low amounts of the complexes, various aryl iodides and bromides were efficiently coupled with phenylacetylene even at room temperature. Furthermore, the catalysts were also effective for the reactions of aryl chlorides. It is noteworthy that this catalyst system employed mild, efficient, aerobic, solvent-free, and copper-free conditions.

Key words

palladium - β-oxoiminatophosphane - catalysis - arylated alkynes - Sonogashira reaction

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General Procedure for the Synthesis of β-Oxoimines 2,4-Pentanedione (11.0 mmol) and primary amines (10.0 mmol) were placed in a 10 mL glass tube. The vessel was sealed with a septum and placed into the microwave cavity. The reaction temperature was raised from r.t. to 130 °C under microwave irradiation of 150 W. The power was maintained for 5 min. After allowing the mixture to cool to r.t., the reaction mixture was vacuumed under reduced pressure. The residue was purified by column chromato-
graphy (SiO2; hexane-ethyl acetate, 4:1) to give β-oxoimine 1 as a liquid.
Compound 1a: light yellow liquid (2.11 g, 96%). 1H NMR (400 MHz, CDCl3): δ = 11.11 (br s, 1 H), 7.23 (t, J = 8.0 Hz, 1 H), 7.17 (d, J = 8.0 Hz, 1 H), 6.91 (t, J = 7.6 Hz, 1 H), 6.85 (d, J = 8.4 Hz, 1 H), 4.99 (s, 1 H), 4.41 (d, J = 6.8 Hz, 1 H), 3.84 (s, 3 H), 2.00 (s, 3 H), 1.92 (s, 3 H). 13C NMR (100 MHz, CDCl3): δ = 194.4, 162.7, 156.6, 128.4, 127.6, 126.0, 120.3, 110.0, 95.3, 55.1, 42.1, 28.7, 18.6. Anal. Calcd for C13H17NO2 (219.28): C, 71.21; H, 7.81; N, 6.39. Found: C, 71.02; H, 7.54; N, 6.58.
Compound 1b: light yellow liquid (1.68 g, 98%). 1H NMR (400 MHz, CDCl3): δ = 10.833 (br s), 4.96 (s, 1 H), 3.45 (t, J = 6.0 Hz, 2 H), 3.35 (s, 3 H), 3.32 (q, J = 8.0 Hz, 2 H), 2.00 (s, 3 H), 1.93 (s, 3 H), 1.83 (t, J = 6.0 Hz, 2 H). 13C NMR (100 MHz, CDCl3): δ = 193.6, 162.4, 94.5, 68.7, 58.0, 39.2, 29.7, 28.1, 18.1. Anal. Calcd for C9H17NO2 (171.24): C, 63.13; H, 10.01; N, 8.18. Found: C, 63.41; H, 10.18; N, 8.21.
Compound 1c: light yellow liquid (1.34 g, 95%). 1H NMR (400 MHz, CDCl3): δ = 10.94 (br s, 1 H), 4.94 (s, 1 H), 3.20 (q, J = 3.6 Hz, 2 H), 1.97 (s, 3 H), 1.91 (s, 3 H), 1.61 (q, J = 3.6 Hz, 2 H), 0.98 (t, J = 7.2 Hz, 3 H). 13C NMR (100 MHz, CDCl3): δ = 193.4, 162.2, 94.2, 44.0, 28.0, 22.8, 18.1, 10.7. Anal. Calcd for C8H15NO (141.21): C, 68.04; H, 10.71; N, 9.02. Found: C, 68.17; H, 10.79; N, 9.32.
Compound 1d: light brown liquid (1.45 g, 93%). 1H NMR (400 MHz, CDCl3): δ = 11.24 (br s, 1 H), 4.87 (s, 1 H), 2.03 (s, 3 H), 1.95 (s, 3 H), 1.37 (s, 9 H). 13C NMR (100 MHz, CDCl3): δ = 193.6, 163.0, 96.1, 52.2, 30.7, 28.7, 20.4. Anal. Calcd for C9H17NO (155.13): C, 69.63; H, 11.04; N, 9.02. Found: C, 69.54; H, 11.38; N, 9.13.

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CCDC-608595 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/ data_request/cif.

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General Procedure for the Synthesis of Palladium(II) β-Oxoiminatophosphanes 2 A solution of EtOTl (0.3 g, 1.2 mmol) in THF (10 mL) was added dropwise at r.t. to a solution of β-oxoimine 1 (1.0 mmol) in THF (10 mL). After being stirred at r.t. for 1 h, a solution of Pd2 (µ-Cl)2Me2 (PPh3)2 (0.51 g, 0.6 mmol) in THF (5 mL) was added dropwise to the mixture. The reaction mixture was stirred at r.t. for 1 h. The mixture was then filtered through Celite on a frit. The solvent was removed under reduced pressure and the residue was washed with hexane (30 mL). Removal of the solvent gave Pd complex 2.
Compound 2a: light brown solid (0.45 g, 75%). 1H NMR (400 MHz, CDCl3): δ = 7.59-7.17 (m, 17 H), 6.92 (t, J = 4.0 Hz, 1 H), 6.81 (d, J = 4.4 Hz, 1 H), 4.83 (s, 1 H), 4.72 (d, J = 3.6 Hz, 2 H), 3.81 (s, 3 H), 1.89 (s, 3 H), 1.61 (s, 3 H),
-0.08 (d, J = 3.2 Hz, 3 H). 13C NMR (100 MHz, CDCl3): δ = 178.0, 166.7, 156.0, 134.9, 134.8, 131.4, 131.0, 129.9, 129.9, 127.8, 127.7, 127.1, 126.6, 120.3, 109.2, 97.6, 55.2, 49.0, 26.4, 23.3, 23.2, -0.8. 31P NMR (162 MHz, CDCl3):
δ = 44.31. Anal. Calcd for C32H34NO2PPd (602.01): C, 63.84; H, 5.69; N, 2.33. Found: C, 63.74; H, 5.53; N, 2.10.
Compound 2b: light brown solid (0.39 g, 73%). 1H NMR (400 MHz, CDCl3): δ = 7.70-7.34 (m, 15 H), 4.70 (s, 1 H), 3.60 (m, 2 H), 3.42 (t, J = 6.0 Hz, 2 H), 3.32 (s, 3 H), 2.01 (s, 3 H), 1.90 (t, J = 7.2 Hz, 2 H), 1.53 (s, 3 H), 0.10 (d, J = 3.6 Hz, 3 H). 13C NMR (100 MHz, CDCl3): δ = 162.7, 141.9, 129.0-126.5 (PPh3, 18C), 95.3, 63.8, 51.8, 50.2, 30.7, 26.4, 24.8, 11.9. 31P NMR (162 MHz, CDCl3): δ = 43.76. Anal. Calcd for C28H34NO2PPd (553.97): C, 60.71; H, 6.19; N, 2.53. Found: C, 61.12; H, 6.00; N, 2.25.
Compound 2c: brown solid (0.37 g, 71%). 1H NMR (400 MHz, CDCl3): δ = 7.81-7.26 (m, 15 H), 4.69 (s, 1 H), 3.44 (m, 2 H), 2.00 (s, 3 H), 1.62 (m, 2 H), 1.52 (s, 3 H), 0.91 (t, J = 7.2 Hz, 3 H), 0.09 (d, J = 3.6 Hz, 3 H). 13C NMR (100 MHz, CDCl3): δ = 176.8, 164.0, 134.8-127.7 (PPh3, 18 C), 97.7, 52.1, 26.2, 25.7, 23.5, 22.6, 11.5, 11.5, 1.8. 31P NMR (162 MHz, CDCl3): δ = 43.75. Anal. Calcd for C27H32NOPPd (523.94): C, 61.89; H, 6.16; N, 2.67. Found: C, 61.66; H, 5.71; N, 3.06.
Compound 2d: brown solid (0.41 g, 76%). 1H NMR (400 MHz, CDCl3): δ = 7.70-7.37 (m, 15 H), 5.27 (s, 1 H), 2.01 (s, 3 H), 1.71 (s, 3 H), 1.15 (s, 9 H) 0.55 (t, 3 H, J = 2.0 Hz). 13C NMR (100 MHz, CDCl3): δ = 158.1, 157.7, 152.1, 151.4, 150.6, 135.6, 132.5, 131.4, 127.5, 127.4, 123.6, 123.5, 123.0, 93.5, 50.1, 30.0, 24.8, 23.4, 19.2, 19.0, 0.8. 31P NMR (162 MHz, CDCl3): δ = 44.11. Anal. Calcd for C28H34NOPPd (537.14): C, 62.51; H, 6.37; N, 2.60. Found: C, 62.40; H, 5.78; N, 3.10.

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General Procedure for the Preparation of Sonogashira Reaction Reactions were carried out in a glass vial equipped with a Teflon screw cap. Aryl halide (1.0 mmol), phenylacetylene (1.1 mmol), piperidine (2.0 mmol), and a catalytic amount of Pd complex 2 were mixed. The resulting mixture was stirred at the appropriate temperature. The samples were withdrawn periodically and analyzed by GC and GC-MS. The GC yield was determined using n-dodecane as an internal standard and based on the amount of aryl halide employed. The reaction mixture was filtered and washed with H2O and Et2O several times. The organic phase was separated and dried over MgSO4, and then the solvent was evaporated under reduced pressure. The product was isolated by column chromatography on SiO2.