Isomerization of Alkynes to 1,3-Dienes under Rhodium or Palladium Catalysis

Abstract

Treatment of 1-aryl-1-octyne with allyltributylstannane under rhodium catalysis provided 1-aryl-1,3-octadiene in good yield. A combination of allyl acetate and a palladium catalyst also effected the isomerization of alkynes to 1,3-dienes.

Key words

rhodium - palladium - isomerization - alkynes - 1,3-dienes

References and Notes

• 1a Trost BM. Schmidt T. J. Am. Chem. Soc.  1988,  110:  2301 
• 1b Ma D. Lin Y. Lu X. Yu Y. Tetrahedron Lett.  1988,  29:  1045 
• 1c Ma D. Yu Y. Lu X. J. Org. Chem.  1989,  54:  1105 
• 1d Ma D. Lu X. Tetrahedron Lett.  1989,  30:  843 
• Isomerization of propargyl ethers:
• 2a Hirai K. Suzuki H. Morooka Y. Ikawa T. Tetrahedron Lett.  1980,  21:  3413 
• 2b Isomerization of perfluoroalkylalkynes: Wang Z. Lu X. Tetrahedron  1995,  51:  11765 
• 2c Isomerization as a side reaction: Kadota I. Shibuya A. Lutete LM. Yamamoto Y. J. Org. Chem.  1999,  64:  4570 
• 2d Ruthenium-catalyzed isomerization: Shiotsuki M. Ura Y. Ito T. Wada K. Kondo T. Mitsudo T. J. Organomet. Chem.  2005,  689:  3168 
• 4a General Procedure for Rhodium-Catalyzed Isomerization of Alkynes. [RhCl(cod)]₂ (4.9 mg, 0.01 mmol) was placed in a 20 mL reaction flask under argon. TMEDA (2.3 mg, 0.02 mmol, dissolved in 2 mL of xylene), alkyne 1b (93 mg, 0.50 mmol, dissolved in 2 mL of xylene), and allyltributylstannane (199 mg, 0.6 mmol, dissolved in 2 mL of xylene) were sequen-tially added at ambient temperature. After being stirred for 12 h at 140 °C, the reaction mixture was cooled to ambient temperature, and HCl (6 M, 5 mL) was added. After being stirred for additional 1 h, the product was extracted with hexane (2 ×10 mL). The combined organic phase was dried over Na₂SO₄. Evaporation followed by silica gel column purification afforded 1,3-diene 2b (78.2 mg, 0.42 mmol, 84%). The obtained 2b showed the identical spectra in the literature, see: Miyaura N. Yamada K. Suginome H. Suzuki A. J. Am. Chem. Soc.  1985,  107:  972 
• 4b

  General Procedure for Palladium-Catalyzed Isomerization of Alkynes. Pd(OAc)₂ (5.6 mg, 0.025 mmol) and PPh₃ (26 mg, 0.10 mmol) were placed in a 20 mL reaction flask under argon. Allyl acetate (60 mg, 0.60 mmol, dissolved in 2 mL of xylene) and alkyne 1a (161 mg, 0.50 mmol) were sequentially added at ambient temperature. After being stirred for 5 h at 140 °C, the reaction mixture was filtered. Evaporation followed by silica gel column purification afforded 1,3-diene 2a (156 mg, 0.49 mmol, 97%).
  1,3-Diene 2a: IR (neat): 2962, 2932, 1645, 1468, 1381, 1279, 1134, 986, 939, 893, 846, 684 cm^-1. ¹H NMR (500 MHz, CDCl₃): δ = 0.92 (t, J = 7.5 Hz, 3 × 0.85 H), 0.96 (t, J = 7.5 Hz, 3 × 0.15H), 1.33-1.49 (m, 4 H), 2.20 (dt, J = 7.5, 6.5 Hz, 2 × 0.85 H), 2.35 (dt, J = 7.5, 6.0 Hz, 2 × 0.15 Hz), 5.70 (dt, J = 10.5, 7.5 Hz, 1 × 0.15 H), 5.99 (dt, J = 15.0, 7.5 Hz, 1 × 0.85 H), 6.16-6.26 (m, 1 H), 6.47 (d, J = 16.0 Hz, 1 × 0.85 H), 6.56 (d, J = 16.0 Hz, 1 × 0.15 H), 6.89 (dd, J = 16.0, 10.5 Hz, 1 × 0.85 H), 7.19 (ddd, J = 16.0, 11.0, 1.0 Hz, 1 × 0.15 H), 7.68 (s, 1 × 0.85H), 7.70 (s, 1 × 0.15H), 7.77 (s, 2 × 0.85 H), 7.80 (s, 2 × 0.15H). ¹³C NMR (125.7 MHz, CDCl₃): δ (1E,3E isomer) = 14.11, 22.45, 31.41, 32.81, 120.34-120.37 (m), 123.56 (q, J = 273 Hz), 125.86 (m), 126.76, 129.80, 132.06 (q, J = 33.2 Hz), 132.45, 139.65, 140.02; δ (1E,3Z isomer) = 14.17, 22.53, 28.11, 31.91, 120.58-120.64 (m), 126.08 (m), 127.97, 128.12, 128.91, 132.12 (q, J = 32.7 Hz), 136.76, 139.97; the signals for the carbons of CF₃ were not observed. Anal. Calcd for C₁₆H₁₆F₆ (%): C, 59.63; H, 5.00; Found: C, 59.70; H, 4.94.

3

The role of allyltributylstannane is not clear at this stage. The formation of chlorotributylstannane was confirmed upon mixing equimolar amounts of [RhCl(cod)]₂ and allyltributyl-stannane in refluxing xylene.