A degassed mixture of isopropyl 2(S)-(tert-butoxycarbonylamino)-5-hydroxypentanoate (product of step 26C, 17.6 g, 63.9 mmol), allyl methyl carbonate (24.0 ml, 213 mmol), Pd2(dba)3 (1.62 g, 1.78 mmol) and BINAP (4.42 g, 7.10 mmol) in THF (150 mL) was refluxed under nitrogen for 3 hours. After cooling to room temperature, the reaction was diluted with ether, filtered through celite and evaporated giving a dark brown syrup. Flash chromatography of the residue (silica gel, 30% ether/hexane) gave isopropyl 5-allyloxy-2(S)-(tert-butoxycarbonylamino)pentanoate as a viscous colorless oil, 16.3 g (81%): 1H NMR (300 MHz, Chloroform-D) δ 5.88 (ddt, 1H, 17.4, 10.4, 5.5), 5.28 (m, 1H), 5.22-5.11 (m, 1H), 5.02 (sept., 1H, J=6.2 Hz), 4.21 (br t, 1H, J=6.7 Hz), 3.94 (dt, 2 H, J=5.9, 1.5 Hz), 3.42 (t, 2H, J=5.9 Hz), 1.90-1.82 (m, 1H), 1.75-1.57 (m, 3H), 1.42 (s, 9H), 1.21 (d, 3H, J=6.2 Hz), 1.19 (d, 3H, J=6.2 Hz). LCMS m/z 316 (M+H)+.
