[CH3:1][O:2][C:3]([CH:5]1[CH2:11][CH2:10][CH:9]2[N:12]([C:13]([O:15][C:16]([CH3:19])([CH3:18])[CH3:17])=[O:14])[CH:6]1[CH2:7][CH2:8]2)=[O:4].I[CH2:21][CH2:22][CH3:23].C[Si]([N-][Si](C)(C)C)(C)C.[K+].C1(C)C=CC=CC=1.[Cl-].[NH4+]>O1CCCC1>[CH3:1][O:2][C:3]([C:5]1([CH2:21][CH2:22][CH3:23])[CH2:11][CH2:10][CH:9]2[N:12]([C:13]([O:15][C:16]([CH3:19])([CH3:18])[CH3:17])=[O:14])[CH:6]1[CH2:7][CH2:8]2)=[O:4]8-Azabicyclo[3.2.1]octane-2,8-dicarboxylic acid 8-tert-butyl ester 2-methyl ester as a mixture of endo and exo isomers from Step 5 (1.0 g, 3.7 mmol) was dissolved in tetrahydrofuran (30 mL), and 1-iodopropane (3.2 g, 19 mmol) was added. The resulting solution was cooled to −76° C. and treated dropwise over 15 minutes with solution of potassium bis(trimethylsilyl) amide in toluene (0.5 M, 11.1 mL, 5.6 mmol). Stirring was continued at −76° C. for 1.5 hours, and the reaction mixture was then allowed to warm slowly to 0° C. over 3 hours. Saturated aqueous ammonium chloride was added, and the resulting mixture was extracted with ethyl acetate. The combined organic extracts were washed with water and brine, dried over sodium sulfate, filtered, and concentrated under reduced pressure. The residue was purified by flash chromatography (silica gel, ethyl acetate/hexane) to provide 2-propyl-8-aza-bicyclo[3.2.1]octane-2,8-dicarboxylic acid 8-tert-butyl ester 2-methyl ester as a mixture of endo and exo isomers as a pale yellow oil (0.99 g, 85% yield).
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