Charge a 2-necked round bottom flask under nitrogen atmosphere with ditert-butyl(1S,2S,4S,5R,6R)-2-(tert-butoxycarbonylamino)-4-hydroxy-bicyclo[3.1.0]hexane-2,6-dicarboxylate (20.7 g, 0.5 mol, see WO03/104217/A2 for synthesis details), 4-dimethylaminopyridine (10.4 g, 0.85 mol), triethylamine (6.98 mL, 0.5 mmol) and p-toluenesulfonyl chloride (10.6 g, 0.55 mol) in dichloromethane (200 mL), and stir the mixture at room temperature overnight. Add 1N solution of potassium hydrogen sulfate (200 mL), water (100 mL) and extract the organic layer. Wash with water (200 mL), brine (200 mL), dry over magnesium sulfate, filter and evaporate to dryness. Add tetrahydrofuran (30 mL) then heptanes (90 mL). Heat the mixture at 60° C. and slowly add more heptanes (200 mL). Cool the mixture to room temperature. Filter the solid and dry under reduced pressure to yield the title compound as a white solid (24.6 g, 87%). MS (m/z): 590 (M+23).
