Reaction Steps
To an oven-dried vial were added N1,N1,N8,N8-tetramethylnaphthalene-1,8-diamine (Proton Sponge®; 1.63 g, 7.60 mmol), tert-butyl((3S,7R,8R,9S)-8-hydroxy-7-isopentyl-9-methyl-2-oxooxonan-3-yl)(methoxymethyl)carbamate (436 mg, 1.086 mmol), anhydrous Na2SO4 (1.15 g, 8.10 mmol), and trimethyloxonium tetrafluoroborate (723 mg, 4.89 mmol) in anhydrous CH2Cl2 (11 mL) at 0° C. The reaction mixture was slowly warmed to room temperature and stirred for 5 h. The reaction mixture was diluted with EtOAc, filtered, and the filtrate was washed with water. The phases were separated and the aqueous phase was extracted with additional EtOAc, and the combined organic phases were washed with 1.0 M aqueous sodium bisulfate (NaHSO4), washed with saturated aqueous NaHCO3, dried over MgSO4, concentrated, and purified by column chromatography on SiO2 (gradient, hexanes/EtOAc) to provide the title compound as a mixture of rotamers in the form of a white solid (320 mg, 71%): IR (neat) 2934, 1747, 1705, 1454, 1366, 1296, 1170, 1080 cm−1; 1H NMR (400 MHz, CDCl3) δ 4.97-4.70 (m, 3H), 4.60-4.47 (m, 0.5H), 4.25-4.11 (m, 0.5H), 3.49 (s, 3H), 3.40-3.28 (m, 3H), 2.97-2.86 (m, 1H), 2.17-2.01 (m, 1H), 1.79-1.42 (m, 16H), 1.42 (d, J=6.4 Hz, 3H), 1.31-1.07 (m, 3H), 0.99-0.82 (m, 7H); 13C NMR (101 MHz, CDCl3) δ 173.54, 155.56, 155.39, 86.39, 81.02, 80.98, 76.34, 75.50, 74.70, 74.43, 61.04, 58.62, 57.11, 55.45, 55.36, 43.42, 36.40, 30.67, 29.62, 28.20, 28.15, 28.09, 27.31, 27.04, 23.05, 22.12, 19.19, 18.10; HRMS-ESI (m/z) ([M]+) calcd for C22H41NO6, 415.2934; found, 415.2943.
