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Compound 6c was prepared likewise Method C starting from 108a (20.5 g, 55.9 mmol), 105a (18.11 g, 55.9 mmol) and KOtBu (6.57 g, 58.7 mmol) to give a yellow oil (31.79 g). Part of this oil (30.63 g) was treated with conc aqueous HCl (23 mL), as described for 106d, to give, after purification by column chromatography (silica, heptane:EtOAc=40:1), 106c (9.83 g, >90% pure by NMR, 43%) as a colorless oil. 1H NMR: δ 4.09 (q, J=7.2 Hz, 2H), 2.38 (t, J=7.2 Hz, 4H), 1.62-1.35 (m, 10H), 1.41 (s, 9H), 1.26-1.17 (m, 2H), 1.24 (t, J=7.2 Hz, 3H), 1.14 (s, 6H), 1.09 (dd, J=6.9, 4.2 Hz, 2H), 0.59 (dd, J=6.3, 3.6 Hz, 2H). 13C NMR: δ 210.5, 177.4, 174.0, 79.8, 60.2, 42.8, 42.6, 42.1, 40.5, 34.0, 28.2 (3×), 27.5, 25.2 (2×), 24.7, 24.3, 24.2, 24.1, 15.3 (2×), 14.4.

1. customto give
2. customafter purification by column chromatography (silica, heptane:EtOAc=40:1), 106c (9.83 g, >90% pure by NMR, 43%) as a colorless oil