[C:1]([O:5][C:6]([NH:8][C:9]1[CH:14]=[CH:13][C:12]([NH:15][C:16]([O:18][C:19]([CH3:22])([CH3:21])[CH3:20])=[O:17])=[CH:11][C:10]=1Br)=[O:7])([CH3:4])([CH3:3])[CH3:2].C([Li])(C)(C)C.CN(C)[CH:31]=[O:32].CCOCC>O>[C:1]([O:5][C:6](=[O:7])[NH:8][C:9]1[CH:14]=[CH:13][C:12]([NH:15][C:16]([O:18][C:19]([CH3:22])([CH3:21])[CH3:20])=[O:17])=[CH:11][C:10]=1[CH:31]=[O:32])([CH3:4])([CH3:3])[CH3:2]3.3 g (0.01 mol) 2,5-bis-tert.-butyloxycarbonylamino-bromobenzene from step A are dissolved in 100 ml of water-free tetrahydrofuran under argon. Gradually 17 ml of a 1.6 molar methyl lithium ether solution (0.03 mol) are added. The reaction mixture is cooled to −20° C. Subsequently 7 ml of 1.5 molar t-butyl lithium solution (0.01 mol) are added gradually. After ending the addition the solution is stirred for 30 minutes at −20° C. Subsequently 1.2 g of dimethylformamide (0.02 mol) are added and the reaction mixture is stirred for an hour at −20° C. After slow heating to room temperature the reaction mixture is hydrolyzed with water and then poured into ether, the aqueous phase is extracted with ether and then the organic phase is dried with magnesium sulfate. The solvent is distilled off in a rotary evaporator and the residue is purified on silica gel with petroleum ether/ethyl acetate (9:1).
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