Sodium borohydride → isopropyl 2(S)-(tert-butoxycarbonylamino)-5-hydroxypentanoate

Participants

Reaction Steps

To a solution of isopropyl 1-(tert-butoxycarbonyl)pyrrolidin-5-one-2(S)-carboxylate (product of step 26B, 49.5 g, 183 mmol) in methanol (300 mL) was added sodium borohydride (10.0 g, 263 mmol) in ˜1 g portions over 1.5 hours. The reaction was stirred under nitrogen for another 10 minutes. It was diluted with water, extracted with ether, combined organic fractions washed with saturated aqueous NaCl, dried (MgSO4) and evaporated to give a light yellow oil. Flash chromatography (silica gel, 20–30% ethyl acetate/hexane) gave 31.8 g (64%) of isopropyl 2(S)-(tert-butoxycarbonylamino)-5-hydroxypentanoate as a colorless syrup: 1H NMR (300 MHz, Chloroform-D) δ 5.16 (br d, 1H, J=7.3 Hz), 5.03 (sept., 1H, J=6.2 Hz), 4.28 (br d, 1H, J=6.2 Hz), 3.67 (br dd, J=10.2, 5.5 Hz), 1.94–1.79 (m, 2H), 1.76–1.67 (m, 1H), 1.66–1.56 (m, 2H), 1.43 (s, 9H), 1.25 (d, 3H, J=6.2 Hz), 1.23 (d, 3H, J=6.2 Hz). LCMS m/z 276 (M+H)+.

Provenance & Evidence