Acetic Acid Mixture with Hydrobromic Acid → (S)-1-[N-(3,5-Dichlorophenyl)-N-phenylcarbamoyl]piperazine-2-carboxylic acid

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Reaction Steps

A mixture of 0.63 g (1.19 mmole) of (S)-4-(benzyloxycarbonyl)-1-[N-(3,5-dichlorophenyl)-N-phenylcarbamoyl]piperazine-2-carboxylic acid and 12 mL of 30% HBr/acetic acid was stirred at room temperature for 40 min, and residual HBr was then removed by bubbling nitrogen through the solution for 3 hr. The mixture was then concentrated in vacuo. The residue was treated with 25 mL of water and the pH adjusted to 7 with aqueous sodium hydroxide. To this mixture was added 45 mL of ethyl acetate, and the ethyl acetate layer was extracted with 5×25 mL of water. The combined water layers were treated with aqueous sodium hydroxide to adjust the pH to 7, and the aqueous was concentrated in vacuo to give 0.73 g of an oily solid, which was carried on immediately in Step F) below.

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