Reaction Steps
Dihydropyran (4.22 mL, 46.2 mmol) was dissolved in EtOAc (30 mL). This solution was stirred 10 minutes in the presence of para-toluenesulphonic acid (catalytic quantity, 20 mg). 17 (2.0 g, 4.62 mmol) was then added in one portion to this solution and allowed to stir for 2 hours. The solution was diluted with EtOAc (70 mL) and washed with saturated aqueous NaHCO3 (50 mL) followed by brine (50 mL). The organic layer was dried (MgSO4), and the solvent removed under vacuum. The oily residue was dried under vacuum to remove any remaining DHP. It was proved pure by TLC (EtOAc) and 18, was retrieved in quantitative yield, 2.38 g (100%). It was used directly in the next step. 1H NMR (CDCl3) as a mixture of 4/5 of diastereoisomers: δ 7.24-7.21 (2H, s×2), 6.88-6.60 (2H, s×2), 5.89-5.73 (4H, m), 5.15-5.04 (6H, m), 4.96-4.81 (2H, m), 4.68-4.35 (4H, m), 4.12-3.98 (4H, m), 3.98-3.83 (8H, m), 3.74-3.63 (8H, m), 3.60-3.40 (8H, m), 2.56-2.50 (4H, m), 2.23-1.93 (12H, m), 1.92-1.68 (10H, m), 1.66-1.48 (20H, m); 13C NMR (CDCl3) δ 173.4, 167.2, 149.1, 132.0, 114.5, 100.0, 98.4, 94.6, 91.7, 68.0, 67.7, 66.3, 63.9, 63.6, 63.3, 62.9, 56.1, 51.6, 51.5, 46.3, 46.3, 31.1, 30.9, 30.7, 30.4, 30.2, 29.0, 25.4, 25.3, 25.2, 24.2, 20.0, 19.8, 19.7; MS (ES+) m/z (relative intensity) 533.2 ([M+H]+, 100).
