[CH3:1][C:2]1([CH2:6][O:7][C:8](=[O:26])[C@@H:9]([NH:15][C:16]([O:18][CH2:19][C:20]2[CH:25]=[CH:24][CH:23]=[CH:22][CH:21]=2)=[O:17])[CH2:10][C:11]([CH3:14])([CH3:13])[CH3:12])[CH2:5][O:4][CH2:3]1.C(N(CC)CC)C>C(Cl)Cl.B(F)(F)F.CCOCC>[CH2:19]([O:18][C:16](=[O:17])[NH:15][C@H:9]([C:8]12[O:4][CH2:5][C:2]([CH3:1])([CH2:3][O:26]1)[CH2:6][O:7]2)[CH2:10][C:11]([CH3:12])([CH3:14])[CH3:13])[C:20]1[CH:25]=[CH:24][CH:23]=[CH:22][CH:21]=1To a solution of 2(S)-benzyloxycarbonylamino-4,4-dimethylpentanoic acid 3-methyl-oxetan-3-ylmethyl ester (21.5 g, 59 mmol) in dry DCM (50 ml) was added BF3.Et2O (0.4 ml, 3.2 mmol). After 5 h, triethylamine (0.9 ml, 6.4 mmol) was added and stirring was continued for 30 min at room temperature. The solvent was evaporated using a rotavap and the resulting oil was redissolved in ethyl acetate and was washed with 50 ml of 3% NH4Cl solution followed by brine. The ethyl acetate layer was dried over MgSO4, the solvent was evaporated and the residue was purified with column chromatography using silica gel and 20:80 EtOAc:Hexane as eluent to give [3,3-dimethyl-1(S)-(4-methyl-2,6,7-trioxabicyclo[2.2.2]oct-1-yl)butyl]carbamic acid benzyl ester (15.5 g).
Wird geladen…