Hydrochloric Acid → 8-Oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid

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Reaction Steps

A mixture of 4 g. (16.7 mmol.) of 7β-amino-3-[(acetyloxy)-methyl]-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid (i.e. 7-ACA), 8.3 ml. (33.4 mmol.) of bis(trimethylsilyl)-acetamide, pulverized molecular sieves (4A, ≃1000 beads), 16 ml. of propylene oxide, and 320 ml. of methylene chloride is stirred at 26° for 1.5 hours under a nitrogen atmosphere. The reaction mixture is cooled to 0° and 10.07 g. (66.8 mmol.) of p-toluenesulfenyl chloride is added dropwise over 20 minutes. The mixture is stirred at ambient temperature for three hours, and then poured into 5% sodium bicarbonate solution. The inorganic layer is acidified by the addition of 1 N HCl and extracted twice with 200 ml. of ethyl acetate. The combined organic extracts are dried over Na2SO4, and then concentrated under reduced pressure to a tan foam. The foam is triturated with ethyl ether to yield 1.75 g. of a tan crystalline material. Recrystallization without heating from methanol/acetone/ether/hexane affords pure pale yellow crystalline 7-[[(4-methylphenyl)thio]imino]-3-](acetyloxy)methyl]-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid; m.p. 204°-205.5°.

Provenance & Evidence