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0 °C

To a solution of methyl [(3R,4R)-3-amino-4-allyl-2-oxoazetidin-1-yl]-3-methylbut-2-enoate (7.0 g) in methylene chloride (110 ml) were added 2,6-lutidine (4.11 ml) and benzyl chloroformate (5.03 ml) at 0° C. and the mixture was stirred for 30 minutes at 0° C. The reaction mixture was diluted with ethyl acetate (800 ml) and the solution was washed with diluted hydrochloric acid, brine, aqueous saturated sodium bicarbonate, and brine. The organic layer was dried over magnesium sulfate and evaporated in vacuo. The residue was chromatographed on silica gel (200 g) eluting with a mixture of methylene chloride and ethyl acetate (20:1-4:1) to give methyl [(3R,4R)-3-benzyloxycarbonylamino-4-allyl-2-oxoazetidin-1-yl]-3-methylbut-2-enoate (10.7 g) as an oil.

1. washthe solution was washed with diluted hydrochloric acid, brine, aqueous saturated sodium bicarbonate, and brine
2. dry with materialThe organic layer was dried over magnesium sulfate
3. customevaporated in vacuo
4. customThe residue was chromatographed on silica gel (200 g)
5. washeluting with a mixture of methylene chloride and ethyl acetate (20:1-4:1)