Propylamine → Ethyl 2-(tert-butoxycarbonylamino)-2-((propylamino)methyl)-6-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)hexanoate

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Reaction Steps

A slurry of ethyl 2-(tert-butoxycarbonylamino)-2-formyl-6-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)hexanoate (172 mg, 0.42 mmol) and propylamine (40 μL, 0.49 mmol, 1.3 equiv) in 1,2-dichloroethane (3 mL) was treated with sodium triacetoxyborohydride (352 mg, 1.66 mmol, 4 equiv). Acetic acid (2 drops, ca 3-5 equiv) was added and the mixture stirred at room temperature for 17 hours then 60° C. for 1 hour. Once the reaction was complete, saturated aqueous sodium bicarbonate was added and the solution was extracted with dichloromethane. The organic extracts were washed with saturated aqueous NaCl, dried over MgSO4, filtered and concentrated. Purification by flash chromatography (0-60% ethyl acetate in hexane) gave ethyl 2-(tert-butoxycarbonylamino)-2-((propylamino)methyl)-6-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)hexanoate as an oil (66 mg, 34%). 1H NMR (CDCl3, 400 MHz) δ 4.16 (m, 2H), 3.5-3.3 (m, 2H), 3.2 (br m, 2H), 2.9 (m, 1H), 1.8-1.6 (m, 4H), 1.5-1.4 (m, 2H), 1.38 (s, 9H), 1.36-1.3 (m, 3H), 1.22 (t, J=7.2 Hz, 3H), 1.18 (s, 12H), 1.05 (m, 1H), 0.75 (t, J=7.4 Hz, 3H), 0.68 (t, J=7.5 Hz, 2H). ESI+ MS: obsd m/z 457 (M+H)+.

Provenance & Evidence