Reaction Steps
To a solution of tert-butyl N-tert-butoxycarbonyl-N-[(3S,7S,8R,9S)-8-hydroxy-9-methyl-7-(1-naphthylmethyl)-2-oxo-1,5-dioxonan-3-yl]carbamate (205 mg, 0.387 mmol), [Pd2(dba)3] (26.6 mg, 0.029 mmol), and dppf (32.5 mg, 0.058 mmol) in toluene (1.94 mL) was added (E) tert-butyl cyclopent-2-en-1-yl carbonate (250 mg, 1.355 mmol), and the mixture was warmed to 95° C. and stirred for 2 h. An additional portion of (E)-tert-butyl pent-2-en-1-yl carbonate (150 mg, 0.6 equiv.) was added to the reaction and stirring continued for an additional 2 h. The mixture was cooled to room temperature and the toluene was removed under reduced pressure. The residue was dissolved in CH2Cl2 (12 mL), adsorbed to Celite® and purified by flash chromatography (SiO2, 35 mL/min, 0→25 EtOAc/hexanes) to provide tert-butyl N-tert-butoxycarbonyl-N-[(3S,7S,8R,9S)-8-cyclopent-2-en-1-yloxy-9-methyl-7-(1-naphthylmethyl)-2-oxo-1,5-dioxonan-3-yl]carbamate (205 mg, 89%) as a mixture of diastereomers (about 1:1) in the form of a white solid: IR (thin film) 2928, 1755, 1709, 1117 cm−1; 1H NMR (400 MHz, CDCl3) δ 8.09 (m, 1H), 7.82 (m, 1H), 7.74-7.66 (m, 1H), 7.53-7.39 (m, 2H), 7.42-7.28 (m, 2H), 6.13-6.01 (m, 1.5H), 6.01-5.92 (m, 0.5H), 5.07 (app t, J=7.7 Hz, 1H), 4.90-4.79 (m, 2H), 4.02-3.83 (m, 2H), 3.76 (dd, J=13.6, 2.8 Hz, 1H), 3.55-3.39 (m, 3H), 2.82-2.66 (m, 1H), 2.60-2.47 (m, 1H), 2.34-2.17 (m, 2H), 2.11-1.92 (m, 3H), 1.57 (app dd, J=12.6, 6.4 Hz, 3H), 1.39 (app d, J=5.9 Hz, 18H); ESIMS m/z 618 ([M+Na]+).
