Boron trifluoride etherate → Leucine, N-carboxy-, N-benzyl ester, L-

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Reaktionsschritte

(2S)-2-Benzyloxycarbonylamino-4-methyl-pentanoic acid 3-methyloxetan-3-ylmethyl ester (Cbz-Leu oxetane ester) (2 g, 5.7 mmol) was dissolved in dry CH2Cl2 (10 mL) under nitrogen. BF3.Et2O (40 μl, 0.3 mmol, 0.054 eq.) was diluted in dry CH2Cl2 (1 mL) and added to the reaction flask. The reaction was allowed to warm up to room temperature and stirred for 12 h. Triethylamine (335 μl, 3.3 mmol, 0.58 eq) was added and the reaction was stirred for an additional 30 min., before being concentrated to thick oil. The crude product was redissolved on EtOAc (15 mL), washed with 3% NH4Cl (10 mL), and saturated NaCl (10 mL), dried (MgSO4), and evaporated to dryness. The reaction yielded a colorless thick oil, which crystallized on standing to give [3-methyl-1-(4-methyl-2,6,7-trioxa-bicyclo[2.2.2]oct-1-yl)-butyl]-carbamic acid benzyl ester, (Cbz-Leu-OBO ester).

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