Compound 2a

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InChIKey HNQRJSXNJWTHPK-MRXNPFEDSA-N

Compound data: CIF

Synthetic procedure: See article for the definitive version of this procedure and for full experimental details.

CuCl (1.5 mg, 15 μmol), ligand 8 (10 mg, 15 μmol), and NaOtBu (1.4 mg, 15 μmol) were dissolved in THF (0.4 mL) and stirred at room temperature for 30 minutes before the addition of pinacolato diboron (140 mg, 0.55 mmol) in THF (0.3 mL). The reaction was further stirred for 10 minutes and boronate 1 (126 mg, 0.500 mmol) was then added along with THF (0.3 mL) and dropwise addition of MeOH (41 μL, 1.00 mmol). After 12 hours of stirring, the reaction mixture was evaporated in vacuo and directly purified by flash silica column chromatography (EtOAc/Hexanes = 1:4) to give 2 (167 mg, 88%) as a colourless solid. The product could be recrystallized from hot MeOH to give X-ray quality crystals (72%). ¹H NMR (500 MHz, CDCl₃) δ 7.09 (dd, J = 8.2, 7.4 Hz, 2H), 7.00 (dd, J = 8.2, 0.9 Hz, 2H), 6.30 (dd, J = 7.2, 0.9 Hz, 2H), 5.87 (br s, 2H), 3.69 (s, 3H), 2.64 (dd, J = 16.8, 9.7 Hz, 1H), 2.54 (dd, J = 16.8, 6.1 Hz, 1H), 1.26 (s, 6H), 1.24 (s, 6H), 1.11 (dd, J = 9.8, 6.3 Hz, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 175.0, 141.0, 136.2, 127.5, 119.5, 117.4, 105.6, 83.5, 51.7, 30.7, 24.9, 24.5. (The boron-bound carbon was not detected due to quadrupolar relaxation of boron). ¹¹B NMR (160 MHz, CDCl₃) δ 33.8, 31.0. IR (Microscope, cm^-1) 3371, 3011, 2989, 2981, 2954, 1728, 1628, 1606, 1520. HRMS (EI) for C₂₀H₂₆B₂N₂O₄: calcd. 380.20786; found 380.20856. [α]_D²⁰: –16.09° (c = 0.22, CH₂Cl₂). M. P. 169–171°C. HPLC (Chiralcel OD): 20:80 i-PrOH/Hexanes, 0.5 mL/minute, λ = 250 nm,T_major = 15.9 min, T_minor = 13.1 min, ee = 99% (prior to recrystallization).