1,1'-Carbonyldiimidazole → 4-O-tert-butyl 1-O-[(Z)-(1,2-diamino-2-oxoethylidene)amino] (2R)-2-(3-cyclohexylpropyl)butanedioate

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Reaction Steps

(R)-2-[2-(tert-Butoxy)-2-oxoethyl]-5-cyclohexylpentanoic acid (Preparation 1) (3.47 g, 11.6 mmol) in dimethylformamide (21 ml) was treated with 1,1′-carbonyidiimidazole (1.97 g, 12.2 mmol) and the mixture was stirred at ambient temperature for 1 hour. N-Dimethylaminopyridine (1.43 g, 11.7 mmol) was then added in one portion, followed by the addition of 2-amino-2-(hydroxyimino)acetamide (1.25 g, 12.1 mmol, Helv.Chim.Acta; 47; 1964; 33-46). The resulting mixture was stirred at room temperature for 24 hours. The mixture was partitioned between ethyl acetate and a 10% solution of citric acid in demineralised water. The layers were separated and the aqueous phase was extracted with ethyl acetate. The combined organic layers were washed with demineralised water (×4) and brine, dried over anhydrous magnesium sulfate, filtered and the solvent removed under reduced pressure. The residue was crystallised from n-hexane, the precipitate was collected by filtration and dried in vacuo to afford the title compound as a colourless solid (3.30 g, 74% yield).

Provenance & Evidence