To a stirred suspension of PPh3 (12.41 g, 47.3 mmol) in THF (100 mL) was added DIAD (9.20 mL, 47.3 mmol) at 10° C. and allowed to stir at 0° C. for 0.5 h. Intermediate 104C (8.0 g, 23.66 mmol) was added as a solution in THF (10 mL) at 0° C. and stirred at RT for 45 min. The reaction mixture was cooled again to 0° C. and tert-butyl (1-hydroxypropan-2-yl)carbamate (5.39 g, 30.8 mmol) was added as a solution in THF (10 mL) and the mixture was stirred at RT for 16 h. The reaction mixture was diluted with ethyl acetate (100 mL), washed with water and brine. The organic layer was dried over Na2SO4, filtered and the filtrate concentrated under reduced pressure. The crude compound was purified by silica gel chromatography (40 g REDISEP® column, eluting with 15% EtOAc in hexane). Fractions containing the product were combined and evaporated to afford the Intermediate 340A as a brown liquid (7.0 g) contaminated with impurities arising from the coupling reagents. MS(ES): m/z=496 [M+H]+. The crude intermediate was taken to the next step without further purification.
