[Cl:1][C:2]1[CH2:8][CH:7]2[N:4]([C:5](=[O:9])[CH2:6]2)[C:3]=1[C:10]([O:12][CH2:13][C:14]1[CH:19]=[CH:18][CH:17]=[CH:16][CH:15]=1)=[O:11].[CH:20]([N-]C(C)C)(C)C.[Li+].CI.[NH4+].[Cl-]>C1COCC1.CCOC(C)=O>[CH3:20][CH:6]1[C:5](=[O:9])[N:4]2[CH:7]1[CH2:8][C:2]([Cl:1])=[C:3]2[C:10]([O:12][CH2:13][C:14]1[CH:19]=[CH:18][CH:17]=[CH:16][CH:15]=1)=[O:11]A solution of benzyl 3-chloro-1-azabicyclo[3.2.0]hept-2-en-7-one-2-carboxylate (56 mg) in anhydrous THF (0.5 ml) is added dropwise over a few minutes to a stirring solution of lithium diisopropylamide (from 31 μl diisopropylamine and 140 μl 1.6N BuLi) in anhydrous THF (3 ml) at -78°. After 15 more mins at -78°, the solution is treated with methyliodide (125 μl) and then allowed to warm to -20° over a period of 30 mins. Saturated aqueous NH4Cl (3 ml) is added and the mixture is allowed to come to room temperature. The mixture is diluted with EtOAc (50 ml), washed with pH 3 phosphate buffer, water, 5% NaHCO3, and brine, dried with magnesium sulfate, and evaporated in vacuo to give benzyl 6-methyl-3-chloro-1-azabicyclo[3.2.0]hept-2-en-7one-2-carboxylate.
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