[Mg].[CH:2]1(Br)[CH2:5][CH2:4][CH2:3]1.[C:7]([O:11][C:12]([N:14]1[CH2:18][CH2:17][C@H:16]([C:19](=[O:24])N(OC)C)[CH2:15]1)=[O:13])([CH3:10])([CH3:9])[CH3:8]>C1COCC1.[H-].C([Al+]CC(C)C)C(C)C.II>[C:7]([O:11][C:12]([N:14]1[CH2:18][CH2:17][C@H:16]([C:19]([CH:2]2[CH2:5][CH2:4][CH2:3]2)=[O:24])[CH2:15]1)=[O:13])([CH3:10])([CH3:9])[CH3:8]
Add diisobutylaluminium hydride (1M in toluene, 0.790 mL, 0.790 mmol) to a stirred mixture of magnesium (0.960 g, 39.5 mmol) and iodine (0.100 g, 0.395 mmol) in THF (1 mL) under nitrogen. Add drop wise a solution of cyclobutyl bromide (8.00 g, 59.2 mmol) in THF (10 mL) and stir the reaction at 60° C. for 2 h whereby all the magnesium is consumed. Cool the mixture to room temperature and add drop wise a solution of (S)-3-(methoxy(methyl)carbamoyl)-pyrrolidine-1-carboxylic acid tert-butyl ester (10.2 g, 39.5 mmol) in THF (50 mL). Stir the reaction mixture at room temperature for 2.5 h. Quench with 1 M aqueous citric acid, extract with EtOAc. Wash the organic layer with water and saturated aqueous NaCl, dry (Na2SO4), filter and concentrate under reduced pressure. Purify the residue by silica gel chromatography, eluting with EtOAc in hexanes (0-50% gradient) to obtain the title compound (5.30 g, 53%).
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