[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([Li])(C)(C)C.CN(C)[CH:33]=[O:34]>O.CCOCC>[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:33]=[O:34])([CH3:4])([CH3:3])[CH3:2]3.3 g (0.01 mol) 2,5-bis-tert.-butyloxycarbonylaminobromobenzene from step A are dissolved in 100 ml of water-free tetrahydrofuran under argon. 17 ml of a 1.6 molar etheric methyl lithium solution (0.03 mol) are gradually added. The reaction mixture is cooled to −20° C., 7 ml of a 1.5 molar tert.-butyl lithium solution (0.01 mol) are gradually added. After the addition has ended the solution is stirred for 30 minutes at the given temperature. Subsequently 1.2 g of dimethyl formamide (0.02 mol) are added and the reaction mixture is stirred for one hour at −20° C. After slowly 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 over magnesium sulfate. The solvent is distilled away in a rotary evaporator and the residue is purified on silica gel with a petroleum ether/ethyl acetate solvent (9/1).
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