To a solution of 17 (0.21 g, 0.51 mmol) and 5-benzyloxy-1-pentyne (133 mg, 0.77 mmol) in N,N-diisopropylethylamine (1 mL, 5.7 mmol) and dry THF (5 mL) were added CuI (9.7 mg, 51 μmol) and tetrakis(triphenylphosphine)palladium(0) (29.5 mg, 25.5 μmol) under nitrogen. The mixture was heated at reflux under nitrogen for one day, and then was cooled to room temperature and filtered through a short pad of silica gel to remove insoluble and very polar components in the mixture. The filtrate was concentrated and dissolved in CH2Cl2 (50 mL). The solution was washed with water (2×20 mL) and brine (2×20 mL), and dried over Na2SO4. The solvent was removed under vacuum and the residue was purified by column chromatography (hexanes/EtOAc 20:1 to 6:1) to give 18 (0.14 g, 53%). 1H NMR δ 7.43-7.19 (m, 4H), 6.49 (d, 1H, J=16.4 Hz), 6.21 (d, 1H, J=16.4 Hz), 5.43 (s, 1H), 4.50 (s, 2H), 3.98 (d, 2H, J=11.2 Hz), 3.87 (d, 2H, J=11.2 Hz), 3.59 (t, 2H, J=6.0 Hz), 2.53 (t, 2H, J=6.8 Hz), 1.89 (m, 2H), 1.45 (s, 15H); 13C NMR δ 154.4, 138.1, 135.5, 131.3, 129.3, 127.9, 127.2, 127.1, 125.9, 122.8, 97.8, 90.1, 80.6, 79.0, 72.5, 68.3, 65.6, 52.7, 28.5, 28.0, 27.1, 19.3, 15.9. HRMS m/z: calcd for C31H39NNaO5 (MNa+), 528.2720; found, 528.2727.
