[C:1]([O:5][C:6](=[O:13])[CH:7]([CH2:9][CH2:10][CH2:11][CH3:12])[NH2:8])([CH3:4])([CH3:3])[CH3:2].C(N(CC)CC)C.[CH3:21][C:22]1([CH3:28])[CH2:24][CH:23]1[C:25](Cl)=[O:26]>C(Cl)Cl>[C:1]([O:5][C:6](=[O:13])[CH:7]([CH2:9][CH2:10][CH2:11][CH3:12])[NH:8][C:25]([CH:23]1[CH2:24][C:22]1([CH3:28])[CH3:21])=[O:26])([CH3:4])([CH3:3])[CH3:2]To a solution of 8.98 g (48 mmole) of DL-norleucine t-butyl ester and 5.05 g (50 mmole) of triethylamine in 100 ml of CH2Cl2 stirred in an ice bath under a drying tube was added dropwise (over a period of 75 min.) a solution of 6.39 g (48 mmole) of 2,2-dimethylcyclopropanecarbonyl chloride (M. Elliot and N. R. James, British Patent No. 1,260,847 (1972)) in 50 ml of CH2Cl2. Precipitation of Et3N HCl occurred during the addition, especially toward the end. As the ice gradually melted, the mixture was allowed to warm to room temperature. After 16 hrs, the mixture was shaken with 200 ml of 0.5 N HCl. The CH2Cl2 fraction was washed with an additional 200 ml of 0.5 N HCl, then with 2×200 ml of 0.5 N NaOH, and finally 200 ml of H2O. The CH2Cl2 fraction was dried with MgSO4, treated with charcoal, and filtered through Celite. The filtrate was concentrated on the rotovac (finally under high vacuum). Yield of light orange residual oil=11.93 g (88%). Tlc (2:1 hexane-EtOAc) showed a single spot. NMR and IR were in accord with the assigned structure. After standing for several days, the unused porition of this material crystallized: m.p. 52°->65°.
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