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.
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.