[Mg].Br[C:3]1[CH:8]=[CH:7][C:6]([O:9][CH2:10][CH2:11][CH2:12][CH2:13][CH2:14][CH2:15][CH2:16][CH2:17][CH2:18][CH2:19][CH2:20][CH2:21][CH2:22][CH3:23])=[CH:5][CH:4]=1.[B:24](OC)([O:27]C)[O:25]C.Cl>C1COCC1.BrCCBr>[CH2:10]([O:9][C:6]1[CH:7]=[CH:8][C:3]([B:24]([OH:27])[OH:25])=[CH:4][CH:5]=1)[CH2:11][CH2:12][CH2:13][CH2:14][CH2:15][CH2:16][CH2:17][CH2:18][CH2:19][CH2:20][CH2:21][CH2:22][CH3:23]Magnesium turnings (1.84 g, 0.08 mol) were added to a stirred solution, at room temperature under dry nitrogen, of compound 31 (15.00 g, 0.040 mol) in dry THF (150 ml) containing 1,2-dibromoethane (2 drops). The reaction mixture was maintained under these conditions for 1 h and then heated under reflux for 1 h. The reaction mixture was cooled to -78° C. and a solution of trimethyl borate (5.75 g, 0.08 mol) in dry THF (50 ml) was added dropwise. The reaction mixture was allowed to warm to room temperature overnight and then stirred for 1 h with 10% hydrochloric acid (100 ml). The product was extracted into ether (twice), and the combined ethereal extracts were washed with water and dried (MgSO4). The solvent was removed in vacuo to yield a white solid.
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