Triphosgene → (2R,4S)-5-biphenyl-4-yl-4-isocyanato-2-methyl-pentanoic acid ethyl ester

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Reaction Steps

To a vigorously stirred 1:1 mixture of methylene chloride/8% aqueous NaHCO3 (30 mL) at 0° C. is added triphosgene (114 mg, 0.384 mmol). After stirring the mixture at 0° C. for 5 minutes, (2R,4S)-4-amino-5-biphenyl-4-yl-2-methyl-pentanoic acid ethyl ester hydrochloride (400 mg, 1.15 mmol) is added and stirring is continued for 15 minutes. The organic phase is separated and dried over sodium sulfate. The solvent is removed under reduced pressure to furnish (2R,4S)-5-biphenyl-4-yl-4-isocyanato-2-methyl-pentanoic acid ethyl ester. Next, to a solution of (2R,4S)-5-biphenyl-4-yl-4-isocyanato-2-methyl-pentanoic acid ethyl ester (1.15 mmol) in methylene chloride (10 mL) is added (S)-pyrrolidine-2-carboxylic acid methyl ester (1.15 mmol) and diisopropylethylamine (2.3 mmol). The mixture is stirred at room temperature for 18 hours. The mixture is washed with aqueous 1M HCl and the organic phase is dried over sodium sulfate and the solvent is removed under reduced pressure. The residue is purified by column chromatography using hexane/methylene chloride to elute the product.

Provenance & Evidence