[H-].[Na+].[CH3:3][O:4][C:5](=[O:23])[C:6]1[CH:11]=[C:10]([N+:12]([O-:14])=[O:13])[CH:9]=[C:8]([NH:15][C:16](=[O:22])[CH2:17][CH2:18][CH2:19][CH2:20]Cl)[CH:7]=1.CO>C1COCC1>[CH3:3][O:4][C:5](=[O:23])[C:6]1[CH:7]=[C:8]([N:15]2[CH2:20][CH2:19][CH2:18][CH2:17][C:16]2=[O:22])[CH:9]=[C:10]([N+:12]([O-:14])=[O:13])[CH:11]=1NaH (60% w/w in mineral oil, 680 mg, 17 mmol, 0.9 equiv) was added portionwise to a solution of 3-(5-chloro-pentanoylamino)-5-nitro-benzoic acid methyl ester (D3) (6 g, 19 mmol, 1 equiv) in THF (40 ml) under nitrogen. The resulting mixture was stirred at room temperature for 1 h and then MeOH was added dropwise. The solution was concentrated in vacuo and the residue diluted with AcOEt. The organic phase was washed with H2O, dried over MgSO4 and concentrated in vacuo. Purification by flash chromatography on silica gel (AcOEt/iso-hexane: 1/2) gave 3-nitro-5-(2-oxo-piperidin-1-yl)-benzoic acid methyl ester (B82) (2.8 g, 53%) as a pale orange oil.
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