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0 °C

An aqueous ethylenediaminetetraacetic acid disodium solution (1.04 ml, 4×10−4 M) was added to a stirred solution of 2-[(tert-butyl-dimethyl-silanyloxy)-cyclohexyl-methyl]-4-(2-chloro-ethyl)-3-methylene-5-oxo-pyrrolidine-2-carboxylic acid methyl ester (71 mg, 0.16 mmol, 1.0 equiv) in acetonitrile (2.6 ml) and the reaction mixture was cooled to 0° C. Trifluoroacetone (0.6 ml) was added via a precooled syringe. A mixture of sodium bicarbonate (0.313 g, 3.72 mmol, 23.25 equiv) and Oxone (0.738 g, 1.2 mmol, 7.5 equiv) was added. The reaction mixture was stirred for 4 h at 0° C. Water (20 ml) was added and the resultant mixture was extracted with dichloromethane (100 ml). The organic layer was separated, dried over sodium sulfate and the solids were filtered. The filtrate was concentrated. Purification of the residue by flash column chromatography (15% ethyl acetate-hexanes initially, grading to 20% ethyl acetate-hexanes) provided 4-[(tert-butyl-dimethyl-silanyloxy)-cyclohexyl-methyl]-7-(2-chloro-ethyl)-6-oxo-1-oxa-5-aza-spiro[2.4]heptane-4-carboxylic acid methyl ester (53 mg, 72%).

1. additionwas added
2. extractionthe resultant mixture was extracted with dichloromethane (100 ml)
3. customThe organic layer was separated
4. dry with materialdried over sodium sulfate
5. filtrationthe solids were filtered
6. concentrationThe filtrate was concentrated
7. customPurification of the residue by flash column chromatography (15% ethyl acetate-hexanes initially