Lithium Hydroxide → 5-{(1R)-1-[(tert-Butoxycarbonyl)amino]ethyl}-1,2-oxazole-3-carboxylic acid

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Reaction Steps

To a stirred solution of (R)-tert-butyl but-3-yn-2-ylcarbamate (262.5 g, 1.56 mol) and (Z)-ethyl 2-chloro-2-(hydroxyimino)acetate (78.2 g, 0.52 mol) in DMF (1 L) was added dropwise Et3N (216 mL, 1.56 mol) at 90° C. The mixture was stirred for 5 hr, and then concentrated in vacuo. The residue was re-dissolved in ethyl acetate. The ethyl acetate solution was washed with water, dried over Na2SO4, and evaporated to provide the crude compound (R)-ethyl 5-(1-(tert-butoxycarbonylamino)ethyl)isoxazole-3-carboxylate. To a solution of (R)-ethyl 5-(1-(tert-butoxycarbonylamino)ethyl)isoxazole-3-carboxylate in THF (2 L) was added aqueous 2.5 N LiOH (1 L) at RT. The mixture was stirred for 1 hr, and then evaporated under reduced pressure to remove THF. The residue was partitioned between water (1 L) and ethyl acetate (0.5 L). The organic layer was separated and the aqueous layer was extracted with ethyl acetate twice. The aqueous layer was adjusted to pH 2 with 10% HCl and extracted with ethyl acetate (2×1 L). All the organic layers were combined, washed with water, dried over Na2SO4, filtered and concentrated under reduced pressure. The residue was dried under vacuum to give the crude product N.4, (R)-5-(1-(tert-butoxycarbonylamino)ethyl)isoxazole-3-carboxylic acid (55.2 g, 44.8%), which was used without further purification. 1H NMR (CDCl3) δ 6.57 (s, 1H), 4.12 (q, 1H), 1.56 (d, 3 H), 1.37 (s, 9H).

Provenance & Evidence