Lithium Hydroxide → (3R,4R)-4-benzyloxycarbonylamino-piperidine-1,3-dicarboxylic acid 1-tert-butyl ester

In a flask (3R,4R)-4-benzyloxycarbonylamino-piperidine-1,3-dicarboxylic acid 1-tert-butyl ester 3-ethyl ester (2.98 g, 7.33 mmol) was dissolved in tetrahydrofuran (120 mL) and lithium hydroxide (15 mL of a 1N aqueous solution, 15 mmol) was added. The mixture was stirred for 68 hours. The reaction was concentrated in vacuo to one-third the original volume. Water (50 mL) and diethyl ether (50 mL) were added and the layers separated. The aqueous layer was extracted with diethyl ether twice (30 mL). The aqueous layer was acidified with aqueous hydrochloric acid (6.5 mL of a 2M solution) and then extracted with ethyl acetate three times (30 mL). The combined organic layers were dried with magnesium sulfate, filtered, and concentrated in vacuo to give a crude white solid (3.11 g) which was used without further purification. 1H NMR (300 MHz, CDCl3), δ: 7.36 (m, 5H), 5.12 (m, 2H), 4.91 (bs, 1H), 4.24 (bs, 1H), 4.09 (bs, 1H), 3.92 (bs, 1H), 3.01 (bs, 1H), 2.87 (m, 1H), 2.44 (m, 1H), 2.05 (bs, 1H), 1.45 (s, 9H), 1.40 (m, 1H).