Ethyl 2-(acetoxymethyl)-2-(tert-butoxycarbonylamino)hex-5-enoate → Ethyl 2-(acetoxymethyl)-2-(tert-butoxycarbonylamino)-6-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)hexanoate

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While under an argon atmosphere, a solution of chloro(1,5-cyclooctadiene)iridium(I) dimer (160 mg, 0.23 mmol) and 1,2-bis(diphenyl-phosphino) ethane (190 mg, 0.48 mmol) in dichloromethane (50 mL) was treated with pinacol borane (7.78 g, 61 mmol, 8.8 mL) and stirred for 15 minutes. To this mixture was added a solution of ethyl 2-(acetoxymethyl)-2-(tert-butoxycarbonylamino)hex-5-enoate (10 g, 30.4 mmol) in dichloromethane (50 mL). After stirring for 19 h at room temperature the solution was concentrated and purified using a combiflash system (120 g column, eluting with 5-50% ethyl acetate in heptanes) to give ethyl 2-(acetoxymethyl)-2-(tert-butoxycarbonylamino)-6-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)hexanoate (7.5 g, 54%). 1H NMR (CDCl3) δ 5.49 (bs, 1H), 4.72 (d, 1H), 4.33 (d, 1H), 4.23 (q, 2H), 2.18 (m, 1H), 2.01 (s, 3H), 1.69 (m, 2H), 1.43 (s, 9H), 1.29 (m, 4H), 1.23 (s, 12H), 0.88 (t, 3H), 0.74 (t, 2H). MS found for C22H40BNO8 m/z [480(M+Na)].

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