Malonic Acid → 4-nitrobenzyl 4-[(2R,3S)-3-{1-methyl-1-(4-nitrobenzyloxycarbonyloxy)ethyl}-4-oxoazetidin-2-yl]-3-oxobutanoate

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Reaction Steps

To a solution of [(2R,3S)-3-{1-methyl-1-(4-nitrobenzyloxycarbonyloxy)ethyl}-4-oxoazetidin-2-yl]-acetic acid (56.4 mg) in tetrahydrofuran (1.13 ml) was added N,N'-carbonyldiimidazole (27.5 mg) at ambient temperature. After stirring for 6 hours at ambient temperature, the magnesium salt of the mono-p-nitrobenzyl ester of malonic acid (84.8 mg) was added and the resulting mixture was stirred overnight at ambient temperature. The solvent was distilled off and the residue was dissolved in ethyl acetate (30 ml) and filtered with a diatomaceous earth. The filtrate was washed with 1N hydrochloric acid, water, phosphate buffer solution (pH 6.8), and saturated aqueous sodium chloride. After drying over magnesium sulfate, the ethyl acetate extract was filtered and evaporated in vacuo. The residual oil (78.8 mg) was chromatographed on silica gel (1.6 g) eluting with a mixture of methylene chloride and ethyl acetate (10:1 to 2:1) to give 4-nitrobenzyl 4-[(2R,3S)-3-{1-methyl-1-(4-nitrobenzyloxycarbonyloxy)ethyl}-4-oxoazetidin-2-yl]-3-oxobutanoate (64.2 mg) as an amorphous solid.

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