water, 894.0 mmol, 12.0 equiv). After being stirred at reflux for 15 min, 22.8 mL of H2O2 were added. This last procedure was repeated twice. The mixture was filtered on a celite pad and diluted with Et2O. The organic layer was successively washed with water, a saturated solution of sodium thiosulfate and brine, dried over MgSO4, filtered and concentrated in vacuo. The resulting alcohol (6a) was used directly in the next step without further purification.
2. A solution of 11.5 mL of dimethylsulfoxide (162.2 mmol, 2.6 equiv) in 112 mL of CH2Cl2 was added dropwise at –78 °C to a solution of 7.1 mL of oxalyl chloride (81.1 mmol, 1.3 equiv) in 292 mL of CH2Cl2. After 15 min, a solution of the preceding compound (62.4 mmol, 1.0 equiv) in 160 mL of CH2Cl2 was added slowly. After the solution was stirred at –78 °C for 15 min, 45.1 mL of triethylamine (326.2 mmol, 5.2 equiv) were added. The reaction mixture was immediately warmed to room temperature, diluted with Et2O, washed successively with a saturated solution of NH4Cl and brine, dried over MgSO4, filtered and concentrated in vacuo. Purification by flash chromatography (PE) furnished aldehyde 7a (11.4 g, 72% over 3 steps). IR (neat) 3060, 2950, 2680, 1680, 1590, 1420, 725, 700 cm-1 – 1H NMR (200 MHz, CDCl3) d 9.48 (s, 1H), 7.57-7.54 (m, 2H), 7.42-7.39 (m, 3H), 6.86 (d, J = 1.0 Hz, 1H), 1.84 (d, J = 1.2 Hz, 3H), 0.53 (s, 6H). – 13C NMR (50 MHz, CDCl3) d 193.3 (III), 153.4 (IV), 150.9 (III), 136.9 (IV), 133.7 (2C, III), 129.5 (III), 128.1 (2C, III), 13.6 (I), -2.0 (2C, I). – CIMS 222 (MNH4+, 100), 336 (65), 152 (45), 110 (35), 204 (M, 30).152 (100), 102 (78). – Anal. Calcd. for C12H16OSi: C, 70.53; H, 7.89. Found: C, 70.41; H, 8.04.
3-(tert-Butyldimethylsilyl)-2-methyl-propenal (7b). The procedure used was the same as for 7a; (7b) was previously described.6
2-Methyl-3-(triisopropylsilyl)-prop-2-en-1-ol (6c) and 2-[triisopropylsilyl)-methyl]-prop-2- en-1-ol (6c') were prepared following the procedure described for (6a). (5.38 g, 50%, inseparable 60:40 mixture of 6c:6c'). (6c) IR (neat) 3370, 2940, 2850, 1660, 1460, 1370, 1240, 830, 775 cm-1 – 1H NMR (400 MHz, CDCl3) d 4.95 (d, J = 1.5 Hz, 1H), 4.80 (d, J = 1.3 Hz, 1H), 4.06 (s, 2H), 1.63 (s, 2H), 1.21 (m, 3H), 1.09 (s, 18H). – 13C NMR (100 MHz, CDCl3) d 154.3 (IV), 116.2, (III), 69.5 (II), 18.9 (6C, I), 18.7 (I), 12.3 (3C, III). (6c') IR (neat) 3370, 2940, 2850, 1660, 1460, 1370, 1240, 830, 775 cm-1 – 1H NMR (400 MHz, CDCl3) d 5.44 (s, 1H), 4.06 (s , 2H), 1.79 (s, 3H), 1.21 (m, 3H), 1.09 (s, 18H). – 13C NMR (100 MHz, CDCl3) d 154.3 (IV), 107.8 (IV), 67.3 (II), 19.7 (II), 18.9 (6C, I), 11.5 (3C, III).
1-(Dimethylphenylsilyl)-2-methyl-7-(trimethylsilyl)-hept-1-en-6-yn-3-ol (8a). A 1M THF solution of ZnCl2 (56.1 mL, 56.1 mmol, 3.3 equiv) was added to magnesium turnings (1.83 g, 76.5 mmol, 4.5 equiv). Some drops of 1,2-dibromoethane were added followed by a slow addition of (4-chloro-but-1-ynyl)-trimethylsilane (8 g, 51 mmol, 3 equiv). After being heated at reflux for 4 h and then cooled to –20 °C, a solution of CuCN (8.95 g, 100 mmol, 6 equiv) and LiCl (8.46 g, 200 mmol, 12 equiv) in THF (200 mL) was added to the reaction mixture. After being stirred for 15 min, the temperature was cooled down to –78 °C and successively, a solution of 7a (3.46 g, 17 mmol, 1 equiv) in THF (50 mL) and Et2O•BF3 (6.3 mL, 51 mmol, 6 equiv) were added. After being stirred for 2h at –30 °C, the temperature was cooled to –78 °C and the reaction mixture was hydrolyzed with a solution of NH4Cl/NH4OH (2/1), diluted with Et2O. The
