Add 1M lithium tri(sec-butyl)borohydride in tetrahydrofuran (42.27 mL, 42.27 mmol) dropwise to di-tert-butyl (1S,2S,5R,6R)-2-[(tert-butoxycarbonyl)amino]-4-oxobicyclo[3.1.0]hexane-2,6-dicarboxylate (7.10 g, 17.25 mmol, see WO03/104217/A2 for synthesis details) in tetrahydrofuran (431.35 mL) at 0° C. and stir. After 90 minutes, carefully add 1M aqueous sodium bicarbonate (60.07 mL, 62.11 mmol) followed by hydrogen peroxide (30% wt, 2.64 mL, 86.27 mmol) at 0° C. The reaction is warmed to room temperature. After 40 minutes, the reaction is extracted with ethyl acetate, washed with 10% aqueous citric acid followed by brine, dried over sodium sulfate, filtered, and concentrated under reduced pressure to give a residue. The residue is purified by flash chromatography eluting with 5-50% ethyl acetate in hexanes to give the title compound (6.70 g, 16.20 mmol, 94%).
