4.4. Ethyl (R,E)-6-((Tert-Butyldimethylsilyl)Oxy)-2,4-Dimethylhex-2-Enoate (11)

To a stirred solution of 9 (6.86 g, 31.5 mmol) in DMSO (50 mL) IBX (10.6 g, 37.8 mmol) was added. After 1 h stirring at 40 °C, the reaction was quenched with water (50 mL) and extracted with ether (2 × 100 mL). The combined organic layers were washed with brine, dried over Na₂SO₄, and removed under vacuum. The residue was refluxed with 10 (22 g, 63 mmol) in toluene (100 mL) at 80 °C for 3 h and the solvent was removed under vacuum. Purification by column chromatography (PE/EA = 40:1) provided pure compound 11 (7 g, 75%) as a colorless oil [22].

¹H NMR (400 MHz, CDCl₃) δ 6.53 (dd, J = 10.1, 1.4 Hz, 1H), 4.17 (q, J = 7.1 Hz, 2H), 3.70–3.41 (m, 2H), 2.80–2.45 (m, 1H), 1.83 (d, J = 1.4 Hz, 3H), 1.66–1.44 (m, 2H), 1.28 (t, J = 7.1 Hz, 3H), 1.00 (d, J = 6.7 Hz, 3H), 0.87 (s, 9H), 0.01 (d, J = 2.1 Hz, 6H). ¹³C NMR (101 MHz, CDCl₃) δ 168.57, 147.56, 126.83, 61.02, 60.52, 39.83, 29.78, 26.04, 20.06, 18.37, 14.42, 12.59, −5.23, −5.25. [α]D20 = −2.167, (c 0.1, CHCl₃). HRMS (ESI+): calcd. for C₁₆H₃₂O₃S_i [M + H]⁺, 301.2193, found 301.2194.