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Synlett 2011(9): 1277-1280  
DOI: 10.1055/s-0030-1260535
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Hydrazone-Promoted Sonogashira Coupling Reaction with Aryl Bromides at Low Palladium Loadings

Takashi Mino*, Saori Suzuki, Kiminori Hirai, Masami Sakamoto, Tsutomu Fujita
Department of Applied Chemistry and Biotechnology, Graduate School of Engineering, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
Fax: +81(43)2903401; e-Mail: tmino@faculty.chiba-u.jp;
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Publikationsverlauf

Received 10 February 2011
Publikationsdatum:
20. April 2011 (online)

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Abstract

The Sonogashira coupling reaction of aryl bromides with a variety of terminal alkynes in DMSO at 125 ˚C gave internal aryl­ated alkynes using low-loaded Pd(acac)2 with hydrazone as a ligand and CuI as the co-catalyst in good yields.

Key words

palladium - catalysis - Sonogashira coupling reaction - hydrazone

7

General Procedure for the Sonogashira Reaction of Aryl Bromides with Alkynes
To a mixture of aryl bromide (1.0 mmol), K3PO4 (1.0 mmol), alkyne (1.2 mmol), CuI (0.005 mmol), and ligand 1a (0.005 or 0.006 mmol) in DMSO (4.0 mL) was added Pd(acac)2 (0.001, 0.01, or 0.1 mol%) in DMSO (0.01 M, 1.0, 10.0, or 100.0 µL) at r.t. under an atmosphere of argon. The mixture was stirred at 125 ˚C for 24 h. The resulting mixture was diluted with EtOAc and H2O. The organic layer was washed with brine, dried over MgSO4, and concentrated under reduced pressure. The residue was purified by silica gel chromatography.
Compound 3a 6c (entry 1, Table  [²] ): 89% as a white solid. ¹H NMR (300 MHz, CDCl3): δ = 2.37 (s, 3 H), 7.14 (d, J = 7.9 Hz, 2 H), 7.30-7.36 (m, 3 H), 7.42 (d, J = 8.1 Hz, 2 H), 7.51-7.54 (m, 2 H). ¹³C NMR (75 MHz, CDCl3): δ = 21.5, 88.7, 89.5, 120.2, 123.5, 128.0, 128.3, 129.1, 131.48, 131.52, 138.4. MS (EI): m/z (%) = 192 (100) [M+]. Compound 3b 8 (entry 2, Table  [²] ): 94% as a brown solid. ¹H NMR (300 MHz, CDCl3): δ = 7.35-7.41 (m, 3 H), 7.51-7.66 (m, 6 H). ¹³C NMR (75 MHz, CDCl3): δ = 87.7, 93.8, 111.4, 118.5, 122.2, 128.2, 128,5, 129.1, 131.8, 132.03, 132.04. MS (EI): m/z (%) = 203 (100) [M+].
Compound 3c 6c (entry 3, Table  [²] ): 88% as a white solid. ¹H NMR (300 MHz, CDCl3): δ = 7.36-7.38 (m, 3 H), 7.52-7.65 (m, 6 H). ¹³C NMR (75 MHz, CDCl3): δ = 87.9, 91.7, 122.5, 123.9 (q, J = 272.0 Hz), 125.3 (q, J = 3.7 Hz), 127.1 (d, J = 1.5 Hz), 128.4, 128.8, 129.9 (q, J = 32.6 Hz), 131.7, 131.8. MS (EI): m/z (%) = 246 (100) [M+].
Compound 3d 6c (entry 4, Table  [²] ): 81% as a yellow solid ¹H NMR (300 MHz, CDCl3): δ = 2.62 (s, 3 H), 7.36-7.38 (m, 3 H), 7.54-7.63 (m, 4 H), 7.93-7.96 (m, 2 H). ¹³C NMR (75 MHz, CDCl3): δ = 26.6, 88.6, 92.7, 122.6, 128.2, 128.3, 128.4, 128.8, 131.68, 131.72, 136.1, 197.3. MS (EI): m/z (%) = 220 (100) [M+].
Compound 3e 6c (entry 6, Table  [²] ): 83% as a brown solid. ¹H NMR (300 MHz, CDCl3): δ = 3.83 (s, 3 H), 6.86-6.89 (m, 2 H), 7.31-7.36 (m, 3 H), 7.46-7.53 (m, 4 H). ¹³C NMR (75 MHz, CDCl3): δ = 55.3, 88.0, 89.3, 114.0, 115.3, 123.6, 127.9, 128.3, 131.4, 133.0, 159.6. MS (EI): m/z (%) = 208 (100) [M+].
Compound 3f 6c (entry 7, Table  [²] ): 67% as a white solid. ¹H NMR (300 MHz, CDCl3): δ = 7.25-7.39 (m, 6 H), 7.51-7.55 (m, 4 H). ¹³C NMR (75 MHz, CDCl3): δ = 89.3, 123.2, 128.2, 128.3, 131.6. MS (EI): m/z (%) = 178 (100) [M+].
Compound 3g 9 (entry 8, Table  [²] ): 91% as a yellow liquid. ¹H NMR (300 MHz, CDCl3): δ = 2.35 (s, 3 H), 7.15 (d, J = 7.6 Hz, 1 H), 7.21-7.26 (m, 1 H), 7.32-7.36 (m, 5 H), 7.51-7.54 (m, 2 H). ¹³C NMR (75 MHz, CDCl3): δ = 20.7, 88.3, 93.3, 123.0, 123.5, 125.6, 128.2, 128.28, 128.33, 129.4, 131.5, 131.8, 140.2. MS (EI): m/z (%) = 192 (100) [M+].
Compound 3h ¹0 (entry 10, Table  [²] ): 82% as a colorless liquid. ¹H NMR (300 MHz, CDCl3): δ = 7.36-7.38 (m, 3 H), 7.45-7.60 (m, 4 H), 7.70 (d, J = 7.7 Hz, 1 H), 7.80 (s, 1 H). ¹³C NMR (75 MHz, CDCl3): δ = 87.8, 90.9, 122.6, 123.7 (q, J = 272.5 Hz), 124.2, 124.7 (q, J = 3.8 Hz), 128.4 (q, J = 4.0 Hz), 128.4, 128.7, 128.9, 131.0 (q, J = 32.7 Hz), 131.7, 134.6 (d, J = 1.0 Hz). MS (EI): m/z (%) = 246 (100) [M+].
Compound 3i ¹¹ (entry 11, Table  [²] ): 60% as a brown liquid. ¹H NMR (300 MHz, CDCl3): δ = 3.82 (s, 3 H), 6.89 (ddd, J = 1.0, 2.6, 8.3 Hz, 1 H), 7.06-7.07 (m, 1 H), 7.12-7.15 (m, 1 H), 7.25-7.28 (m, 1 H), 7.33-7.36 (m 3 H), 7.52-7.55 (m, 2 H). ¹³C NMR (75 MHz, CDCl3): δ = 55.3, 89.2, 89.3, 114.9, 116.3, 123.2, 124.16, 124.24, 128.28, 128.33, 129.4, 131.6, 159.3. MS (EI): m/z (%) = 208 (100) [M+].
Compound 3j ¹² (entry 12, Table  [²] ): 66% as a colorless liquid. ¹H NMR (300 MHz, CDCl3): δ = 2.30 (s, 6 H), 6.97 (s, 1 H), 7.17 (s, 2 H), 7.32-7.37 (m, 3 H), 7.50-7.53 (m, 2 H). ¹³C NMR (75 MHz, CDCl3): δ = 21.1, 88.7, 89.7, 122.8, 123.4, 128.1, 128.3, 129.3, 130.2, 131.6, 137.9. MS (EI): m/z (%): =206 (100) [M+].
Compound 3k 6c (entry 13, Table  [²] ): 42% as a colorless liquid. ¹H NMR (300 MHz, CDCl3): δ = 2.51 (s, 3 H), 7.14-7.24 (m, 3 H), 7.33-7.39 (m, 3 H), 7.49-7.56 (m, 3 H). ¹³C NMR (75 MHz, CDCl3): δ = 20.7, 88.3, 93.3, 123.0, 123.5, 125.6, 128.2, 128.28, 128.32, 129.4, 131.5, 131.8, 140.2.
MS (EI): m/z (%) = 192 (100) [M+].
Compound 3l 9 (entry 14, Table  [²] ): 34% as a yellow liquid. ¹H NMR (300 MHz, CDCl3): δ = 3.91 (s, 3 H), 6.90 (d, J = 8.1 Hz, 1 H), 6.95 (dd, J = 1.0, 7.5 Hz, 1 H), 7.24-7.37 (m, 4 H), 7.49-7.52 (m, 1 H), 7.55-7.58 (m, 2 H). ¹³C NMR (75 MHz, CDCl3): δ = 55.8, 85.6, 93.4, 110.7, 112.4, 120.5, 123.5, 128.0, 128.2, 129.7, 131.6, 133.6, 159.9. MS: m/z (%) = 220 (100) [M+].
Compound 3m 6c (entry 15, Table  [²] ): 84% as a yellow liquid. ¹H NMR (300 MHz, CDCl3): δ = 7.34-7.67 (m, 8 H), 7.77 (dd, J = 1.0, 7.1 Hz, 1 H), 7.83-7.88 (m, 2 H), 8.45 (d, J = 8.2 Hz, 1 H). ¹³C NMR (75 MHz, CDCl3): δ = 87.9, 94.7, 121.3, 123.8, 125.7, 126.6, 126.8, 127.2, 128.7, 128.79, 128.84, 129.2, 130.8, 132.1, 133.6, 133.7. MS: m/z (%) = 228 (100) [M+].
Compound 3n ¹³ (entry 16, Table  [²] ): 34% as a white solid. ¹H NMR (300 MHz, CDCl3): δ = 7.20 (dd, J = 1.1, 5.0 Hz, 1 H), 7.24-7.37 (m, 4 H), 7.49-7.55 (m, 3 H). ¹³C NMR (75 MHz, CDCl3): δ = 84.5, 88.8, 122.3, 123.2, 125.3, 128.2, 128.3, 128.6, 129.9, 131.5. MS: m/z (%) = 184 (100) [M+].
Compound 3o 9 (entry 17, Table  [²] ): 82% as a white solid. ¹H NMR (300 MHz, CDCl3): δ = 2.36 (s, 3 H), 3.82 (s, 3 H), 6.87 (d, J = 8.8 Hz, 2 H), 7.14 (d, J = 7.9 Hz, 2 H), 7.39-7.47 (m, 4 H). ¹³C NMR (75 MHz, CDCl3): δ = 21.5, 55.3, 88.2, 88.6, 113.9, 115.6, 120.5, 129.1, 131.3, 133.0, 138.0, 159.5. MS: m/z (%) = 222 (100) [M+].
Compound 3p 6c (entry 19, Table  [²] ): 59% as a white solid. ¹H NMR (300 MHz, CDCl3): δ = 2.36 (s, 6 H), 7.14 (d, J = 7.9 Hz, 4 H), 7.41 (d, J = 8.1 Hz, 4 H). ¹³C NMR (75 MHz, CDCl3): δ = 21.5, 88.8, 120.3, 129.1, 131.4, 138.2. MS (EI): m/z (%) = 206 (100) [M+].
Compound 3q 6c (entry 20, Table  [²] ): 56% as a white solid. ¹H NMR (300 MHz, CDCl3): δ = 2.37 (s, 3 H), 6.99-7.07 (m, 2 H), 7.15 (d, J = 7.9 Hz, 2 H), 7.41 (d, J = 8.2 Hz, 2 H), 7.46-7.53 (m, 2 H). ¹³C NMR (75 MHz, CDCl3): δ = 21.5, 87.6, 89.2 (d, J = 1.3 Hz), 115.5 (d, J = 22.0 Hz), 119.6 (d, J = 3.5 Hz), 120.0, 129.1, 131.4, 133.4 (d, J = 8.3 Hz), 138.5, 162.4 (d, J = 249.2 Hz). MS (EI): m/z (%) = 210 (100) [M+].
Compound 3r ¹4 (entry 21, Table  [²] ): 69% as a white solid. ¹H NMR (300 MHz, CDCl3): δ = 2.34 (s, 3 H), 2.36 (s, 3 H), 7.12-7.25 (m, 4 H), 7.31-7.43 (m, 4 H). ¹³C NMR (75 MHz, CDCl3): δ = 21.2, 21.5, 88.9, 89.2, 120.2, 123.2, 128.2, 128.6, 129.0, 129.1, 131.5, 132.1, 138.0, 138.3. MS (EI): m/z (%) = 206 (100) [M+].
Compound 3s 6c (entry 22, Table  [²] ): 73% as a white solid. ¹H NMR (300 MHz, CDCl3): δ = 2.37 (s, 3 H), 7.06-7.17 (m, 4 H), 7.25-7.33 (m, 1 H), 7.44-7.54 (m, 3 H). ¹³C NMR (75 MHz, CDCl3): δ = 21.5, 82.0, 94.6 (d, J = 3.3 Hz), 112.1 (d, J = 15.9 Hz), 115.5 (d, J = 20.9 Hz), 119.8, 123.9 (d, J = 3.9 Hz), 129.1, 129.7 (d, J = 8.0 Hz), 131.6, 133.4 (d, J = 1.0 Hz), 138.8, 162.6 (d, J = 251.4 Hz). MS (EI): m/z (%) = 210 (100) [M+].