To a 1 L round bottom flask equipped with a magnetic stir bar and septum was added triphenylphosphine (12.3 g, 47.0 mmol) under an atmosphere of nitrogen. To this was added methylene chloride (500 mL) followed by addition of solid iodine (11.91 g, 47.0 mmol). This was allowed to stir at room temperature for a period of 10 min. then cooled to 0° C. Triethylamine (13.1 mL, 94 mmol) was then slowly added to this reaction (CAUTION: Exotherm). This mixture was allowed to stir at room temperature for an additional ten min., during which the reaction became a thick slurry. N′-((2R,3S)-3-(tert-butyldimethylsilyloxy)-2-(3-chloro-4-cyano-2-methylphenyl-amino)butanoyl)-4-cyanobenzohydrazide (12.35 g, 23.5 mmol) was taken up in methylene chloride (200 mL) and slowly added to the heavily stirred reaction mixture. After a period of 10 min, TLC (1:1 EtOAc:hexanes) showed product formation and no starting material. The reaction was then quenched by slow addition of 10% Na2S2O3/H2O (500 mL). The organic layer was then isolated and washed with additional 10% sodium thiosulfate/water (1×200 mL), brine (1×200 mL), then dried (Na2SO4). The solution was then filtered and concentrated under reduced pressure to reveal a brown oil/so lid. This was purified via silica gel chromatography eluted with 25% EtOAc/hexanes to provide the title compound as a white solid (9.98 g, 84%): 1H NMR (400 MHz, CDCl3, δ in ppm) (AA′XX′, J=8.8 Hz, 2H), 7.79 (AA′XX′, J=8.8 Hz, 2H), 7.33 (d, J=8.7 Hz, 1H), 6.44 (d, J=8.7 Hz, 1H), 5.35 (d, J=8.8 Hz, 1H), 4.82 (dd, J=2.0, 8.7 Hz, 1H), 3.54 (m, 1H), 2.37 (s, 3H), 1.42 (d, J=6.2 Hz, 3H), 0.85 (s, 9H), 0.07 (s, 3H), −0.22 (s, 3H).
