A solution of 50 wt % ®T3P in EtOAc (22.00 mL, 37.0 mmol) was added dropwise via addition funnel to a solution of (2E,4S)-4-({[(1,1-dimethylethyl)oxy]carbonyl}-amino)-2-hexenoic acid (5.65 g, 24.64 mmol), 2,3-dihydro-1H-indole (2.76 mL, 24.64 mmol), and Et3N (11 mL, 79 mmol) in CH2Cl2 (90 mL) at 0° C. (bath temp). The ice bath was removed, and the reaction was stirred at RT. After 30 min, the reaction was quenched by dropwise addition of saturated aq. NaHCO3 (50 mL). The layers were separated, and the reaction was washed with 10% citric acid (1×50 mL). The organic layer was concentrated under a stream of nitrogen, and the residue was purified by flash column chromatography, giving 7.21 g (89%) of the title compound. LC-MS m/z 331 (M+H)+, 1.05 (ret time).
