General procedure for the determination of epimerization
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To a solution of ethyl cis/trans-1-tert-butyl-4-phenyl-azetidin-2-
one-3-carboxylate (30 : 70 cis:trans) (26 mg, 0.1 mmol) in dry
CH2Cl2 (1.5 mL) was added additive indicated in Table 4 at room
temperature. The resulting mixture was stirred for 3–5 h at room
temperature and then was washed with saturated aqueous sodium
bicarbonate (2 ¥ 50 mL) and brine (2 ¥ 50 mL). The organic layer
was dried over anhydrous sodium sulfate. After evaporation of the
solvent, the residue was subjected for 1H NMR analysis in CDCl3.
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Acknowledgements
The project was supported by National Natural Science Founda-
tion of China (Nos. 20772005 and 20472005), specialized Research
Fund for the Doctoral Program of Higher Education, Ministry of
Education of China. Qi and Li contribute equally to this project.
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