O[C@H:2]1[CH2:6][N:5]([C:7]([O:9][C:10]([CH3:13])([CH3:12])[CH3:11])=[O:8])[C@H:4]([C:14]([O:16][CH3:17])=[O:15])[CH2:3]1.ClCCl.C(Br)(Br)(Br)[Br:22].C1(P(C2C=CC=CC=2)C2C=CC=CC=2)C=CC=CC=1>C(OCC)C.CO>[Br:22][C@@H:2]1[CH2:6][N:5]([C:7]([O:9][C:10]([CH3:13])([CH3:12])[CH3:11])=[O:8])[C@H:4]([C:14]([O:16][CH3:17])=[O:15])[CH2:3]11-(tert-Butyl) 2-methyl(2S,4R)-4-hydroxytetrahydro-1H-1,2-pyrroledicarboxylate (3) (2.0 g, 8.15 mmol) was weighed into an oven-dried flask and azeotropically dried using toluene. Dichloromethane (16 mL) and carbon tetrabromide (10.81 g, 8.15 mmol) were added and the solution was stirred, cooled to 0° C. and treated with triphenylphosphine (8.5 g, 32.41 mmol). The mixture was stirred for 5 h at 0° C., then methanol (1.8 mL) was added and stirring was continued overnight at room temperature. The mixture was diluted with diethyl ether (80 ml) and the resulting suspension was filtered and washed with diethyl ether (30 ml). The solvents were combined and evaporated under reduced pressure and the crude product was purified by silica gel column chromatography eluting with hexane/ethyl acetate (19:1 to 4:1, v/v) to give the title bromide (4) (1.0 g, 40%) as a colourless oil:
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