Reaction SMILES: [Si:1]([CH2:5][Mg]Cl)([CH3:4])([CH3:3])[CH3:2].[Si:8]([O:25][CH2:26][CH2:27][C@H:28]([O:50][CH2:51][C:52]1[CH:57]=[CH:56][C:55]([O:58][CH3:59])=[CH:54][CH:53]=1)[CH2:29][C@H:30]1[O:35][C@@H:34]([CH2:36][C@@H:37]([O:44][Si](C)(C)C)[CH2:38]C(OCC)=O)[CH2:33][C:32](=[CH2:49])[CH2:31]1)([C:21]([CH3:24])([CH3:23])[CH3:22])([C:15]1[CH:20]=[CH:19][CH:18]=[CH:17][CH:16]=1)[C:9]1[CH:14]=[CH:13][CH:12]=[CH:11][CH:10]=1.Cl.[CH2:61]1COC[CH2:62]1>>[C:21]([Si:8]([C:15]1[CH:16]=[CH:17][CH:18]=[CH:19][CH:20]=1)([C:9]1[CH:10]=[CH:11][CH:12]=[CH:13][CH:14]=1)[O:25][CH2:26][CH2:27][C@H:28]([O:50][CH2:51][C:52]1[CH:57]=[CH:56][C:55]([O:58][CH3:59])=[CH:54][CH:53]=1)[CH2:29][C@H:30]1[O:35][C@@H:34]([CH2:36][C@@H:37]([OH:44])[CH2:38][C:61]([CH2:5][Si:1]([CH3:3])([CH3:4])[CH3:2])=[CH2:62])[CH2:33][C:32](=[CH2:49])[CH2:31]1)([CH3:22])([CH3:23])[CH3:24]
Reactant: C1CCOC1
Reactant: C=C1C[C@H](C[C@H](CC(=O)OCC)O[Si](C)(C)C)O[C@H](C[C@H](CCO[Si](c2ccccc2)(c2ccccc2)C(C)(C)C)OCc2ccc(OC)cc2)C1
Reactant: C[Si](C)(C)C[Mg]Cl
Agent: Cl
Product: C=C1C[C@H](C[C@@H](O)CC(=C)C[Si](C)(C)C)O[C@H](C[C@H](CCO[Si](c2ccccc2)(c2ccccc2)C(C)(C)C)OCc2ccc(OC)cc2)C1
Temperature: -78 °C
Reaction time: 1 h
Yield: 81 %

Procedure:
A 10 mL rb flask was charged with powered CeCl3.7H2O (773 mg, 2.07 mmol, 10.0 equiv) and heated to 170° C. under vacuum. After 16 h at 170° C., the dry CeCl3 was cooled to rt, and the flask was flushed with N2. THF (2.0 mL) was added via syringe, and the reaction mixture was stirred at rt for 2 h. Meanwhile, to a 25 mL three-necked rb flask equipped with condenser and magnetic stir bar, was added magnesium turnings (124 mg, 5.0 mmol), and a crystal of iodine. The flask was heated with heat gun for 5 min while stirring. THF (5.0 mL) was added into the reaction via syringe, and the reaction mixture was heated with heat gun to reflux. TMSCH2Cl (0.613 g, 5.0 mmol) was then added to the reaction dropwise via syringe. The mixture was stirred at rt for 1.5 h to afford a 1.0 M solution of TMSCH2MgCl. The reaction mixture containing CeCl3 was cooled to −78° C., then a solution of TMSCH2MgCl (2.07 mL, 2.07 mmol, 10.0 equiv) was added to the reaction dropwise via syringe. After 1 h at −78° C., a solution of ester 18 (155 mg, 0.207 mmol, 1.0 equiv) in THF (1.8 mL) was added via cannula. Additional THF (0.2 mL) was used to transfer the remaining ester residue into the reaction mixture. The resulting mixture was allowed to warm to rt and stirred overnight. The reaction was cooled to −78° C., and then a 1N HCl solution (4.0 mL) was added into reaction dropwise via syringe. The mixture was allowed to warm to rt and the phases were separated. The aqueous phase was extracted with Et2O (3×10 mL). The organic phases were combined, washed with saturated aqueous NaHCO3 solution (10 mL), dried over Na2SO4 and concentrated under reduced pressure. Purification was accomplished by flash column chromatography on a 3×14 cm silica gel column, eluting with 1000 mL hexanes/EtOAc (9:1), collecting 10 mL fractions. The product containing fractions (48-100) were combined and concentrated under reduced pressure to provide hydroxyl allylsilane 5 (120 mg, 81%) as a colorless oil: Rf=0.545 (20% EtOAc/Hexanes); [α]D20=+2.5 (c=0.51, CHCl3); 500 MHz 1H NMR (CDCl3) δ 7.70-7.66 (m, 4H), 7.46-7.36 (m, 6H), 7.20 (m, 2H), 6.83 (m, 2H), 4.72 (dd, J=10.4, 1.7 Hz, 2H), 4.65 (dd, J=15.4, 2.0 Hz, 2H), 4.44 (d, J=10.7 Hz, 1H), 4.38 (d, J=10.7 Hz, 1H), 3.97 (m, 1H), 3.82-3.73 (m, 6H), 3.59-3.48 (m, 3H), 2.26-2.16 (m, 3H), 2.09-2.04 (dd, J=13.8, 6.4 Hz, 1H), 2.00 (t, J=12.1 Hz, 1H), 1.94 (t, J=12.1 Hz, 1H), 1.80 (q, J=6.4 Hz, 2H), 1.73-1.60 (m, 4H), 1.56 (s, 2H), 1.07 (s, 9H), 0.03 (s, 9H); 125 MHz 13C NMR (CDCl3) δ 159.3, 144.7, 144.2, 135.8, 134.1 (×2), 131.1, 129.8 (×2), 129.7, 127.9, 114.0, 110.0, 109.1, 79.3, 75.6, 72.9, 71.6, 69.7, 60.6, 55.5, 46.6, 42.6, 42.0, 41.2, 41.1, 37.6, 27.2, 27.1, 19.4, −1.1; 125 MHz DEPT 13C NMR (CDCl3) CH3 δ 55.5, 27.1, −1.1; CH2 δ 110.0, 109.1, 71.6, 60.6, 46.6, 42.6, 42.0, 41.2, 41.1, 37.6, 27.2; CH δ 135.8, 129.8 (×2), 129.7, 127.9, 114.0, 79.3, 75.6, 72.9, 69.7; CH0 δ 159.3, 144.7, 144.2, 134.1 (×2), 131.1, 19.4; IR (neat) 3504, 3072, 2940, 1653, 1613, 1588, 1514, 1472, 1428, 1361, 1303, 1248, 1116, 1038, 849, 738, 702, 615, 505 cm−1; LRMS (EI) Calcd for C43H63O5Si2 (M+H): 715.4. Found: 715.2.