A solution of 50 wt % ®T3P in EtOAc (1.2 mL, 2.016 mmol) was added dropwise to a solution of [(1S,2E)-4-(2,3-dihydro-1H-indol-1-yl)-1-(2-methylpropyl)-4-oxo-2-buten-1-yl]amine trifluoroacetate (500 mg, 1.343 mmol), 4-((tert-butoxycarbonyl)amino)tetrahydro-2H-pyran-4-carboxylic acid (329 mg, 1.343 mmol), and Et3N (0.93 mL, 6.71 mmol) in CH2Cl2 (5 mL) at 0° C. (bath temp). The ice bath was removed, and the reaction was stirred at RT. After 1 h 20 min, the reaction was washed with saturated aq. NaHCO3 (1×5 mL) and 10% citric acid (1×5 mL). The organic layer was concentrated under a stream of nitrogen, and the residue was purified by flash column chromatography, giving 204 mg (31%) of the title compound. LC-MS m/z 486 (M+H)+, 1.07 min (ret time).
