C1[O:12][C:4]2([CH2:10][CH:9]3[CH2:11][CH:5]2[CH2:6][NH:7][CH2:8]3)OC1.C(N([CH2:18][CH3:19])CC)C.Cl[C:21]([O:23][CH2:24][CH3:25])=[O:22].C(=O)(O)[O-:27].[Na+]>C(Cl)Cl>[CH2:24]1[O:23][C:21]([N:7]2[CH2:6][CH:5]3[CH2:11][CH:9]([CH2:10][C:4]3=[O:12])[CH2:8]2)([O:27][CH2:18][CH3:19])[O:22][CH2:25]13-Azabicyclo[3.2.1]octan-6-one ethylene ketal (7.69 g, 45.5 mmol) was dissolved in methylene chloride (200 ml) and chilled to 0° C. To this solution was added triethylamine (6.34 ml, 91.0 mmol), then ethyl chloroformate (4.02 ml, 50.1 mmol) drop-wise. The reaction was warmed to ambient temperature and stirred for 18 h. Saturated sodium bicarbonate solution (100 ml) was added, and the organic layer was separated. The aqueous layer was saturated with sodium chloride and extracted with methylene chloride (1×100 ml). The organics were then combined, dried over sodium sulfate, filtered and concentrated. The crude brown residue was then distilled on a Kugelrohr apparatus (0.2 mm Hg, unknown temperature) to yield a clear, dark brown oil (6.72 g, 61.3%).
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