Pyrrolidine → 2-Tert-butoxycarbonylamino-2-(2-pyrrolidin-yl-ethyl)-6-(4,4,5,5-tetramethyl-[1,3,2]-dioxaborolan-2-yl)-hexanoic acid ethyl ester

Participants

Reaction Steps

A solution of 2-tert-Butoxycarbonylamino-2-(2-oxo-ethyl)-6-(4,4,5,5-tetramethyl-[1,3,2]-dioxaborolan-2-yl)-hexanoic acid ethyl ester (100 mg, 0.23 mmol, 1.0 equiv.) and pyrrolidine (21 mg, 0.29 mmol, 1.2 equiv.) in 1,2-dichloroethane (0.5 mL) was treated with sodium triacetoxyborohydride (125 mg, 0.59 mmol) in one portion. After stirring at room temperature overnight, the reaction mixture was quenched with saturated aqueous NaHCO3 (1 mL) and stirred for an additional 5 min. The resulting mixture was added to a separatory funnel, diluted with saturated aqueous NaCl (5 mL) and extracted with dichloromethane (2×10 mL). The organic layer was dried over MgSO4, filtered and concentration under reduced pressure. Purification by flash column chromatography eluting with 5% methanol in chloroform to give 2-tert-butoxycarbonylamino-2-(2-pyrrolidin-yl-ethyl)-6-(4,4,5,5-tetramethyl-[1,3,2]-dioxaborolan-2-yl)-hexanoic acid ethyl ester as a pale yellow oil (92 mg, 83%). Rf 0.32 (10% methanol in dichloromethane); 1H NMR (CDCl3, 300 MHz) δ 5.67 (br, s, NH, 1H), 4.19 (m, 2H), 2.46-2.82 (m, 6H), 2.18 (m, 2H), 1.88 (m, 3H), 1.76 (m, 2H), 1.42 (s, 9H), 1.26-1.41 (m, 3H), 1.28 (t, J=7.0 Hz, 3H), 1.22 (s, 12H), 1.06 (m, 1H) and 0.73 (t, J=7.5 Hz, 2H).

Provenance & Evidence