[Mg].[CH3:2][C:3]1([CH3:10])[C:7]([CH3:9])([CH3:8])[O:6][BH:5][O:4]1.Br[CH2:12][C:13]([CH3:15])=[CH2:14].Cl>C1COCC1>[CH3:2][C:3]1([CH3:10])[C:7]([CH3:9])([CH3:8])[O:6][B:5]([CH2:14][C:13]([CH3:15])=[CH2:12])[O:4]1To a suspension of magnesium turning (1.139 g, 46.9 mmol) in THF (65.1 mL) was added 4,4,5,5-tetramethyl-1,3,2-dioxaborolane (5.67 mL, 39.1 mmol) at room temperature under nitrogen. 3-bromo-2-methylprop-1-ene (3.97 mL, 39.1 mmol) was added slowly, after 30 min, more 3-bromo-2-methylprop-1-ene (3.97 mL, 39.1 mmol) was added, The reaction mixture was stirred at room temperature for 1 h. heptanes was added, followed by 1N HCl. The reaction mixture was then extracted by heptanes. The organic was washed by water and brine, dried and concentrated to yield 4,4,5,5-tetramethyl-2-(2-methylallyl)-1,3,2-dioxaborolane. The product was used in the next step without purification, 1H NMR (400 MHz, CDCl3) δ ppm 4.67 (d, J=6.7 Hz, 2H), 1.77 (s, 3H), 1.34-1.20 (m, 12H).
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