Cyclohexene → (Z)-4-[2-(3,5,5,8,8-Pentamethyl-5,6,7,8-tetrahydronaphthalen-2-yl)-2-(trimethylsilyl)vinyl]benzyl Alcohol

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Reaction Steps

A 3-neck 25 mL round bottom flask was fitted with a reflux condenser, and flame-dried under high vacuum. The vacuum was broken by the addition of dry argon (3×), and the flask was allowed to cool to room temperature. The flask was charged with 0.5 mL (1.0 mmol) of borane-methyl sulfide and THF (0.3 mL) and cooled to 0° C. The solution was treated with 0.20 mL (2 mmol) of cyclohexene and stirred at 0° C. for 1 hour. Neat 4-[(trimethylsilyl)ethynyl]benzyl tert-butyldiphenylsilyl ether (Compound 2, 443 mg, 1 mmol) was added and, after 15 minutes the solution was warmed to room temperature and stirred for 2.25 hours. In a second flask was prepared a solution of tetrakis(triphenylphosphine)palladium (0) (58 mg, 0.05 mmol) and 2-bromo-3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydronaphthalene (1.26 g, 4.5 mmol) in 5 mL of THF, which was purged with argon for 10 minutes. The solvents in the first flask were removed under high vacuum, and the residue dissolved in 1 mL of THF and 1 mL of 2 M aqueous NaOH, and the resulting solution was purged with argon for 10 minutes. A 1 mL aliquot of the solution from the second flask was added to the first flask, and the reaction was protected from light and refluxed for 5 hours. The reaction was cooled to room temperature and treated with 2 M NaOH (1 mL) and 30% hydrogen peroxide (0.4 mL). The solution was poured into a separatory funnel containing water and pentane. The layers were separated and the aqueous layer was extracted 3 times with pentane. The combined organic layers were washed once with brine, and dried over magnesium sulfate, and the solvents were removed under reduced pressure. The residue was partially purified by silica gel chromatograhy (99:1, hexane:ethyl acetate). The later fractions were combined and concentrated under reduced pressure. The residue (203 mg) was dissolved in 3.2 mL of THF and treated with 313 mg of tetrabutylammonium flouride (Tbaf) adsorbed onto silica gel (1.6 mmol flouride per gram). The suspension was stirred for 5 hours at room temperature and then the silica gel was washed with ether, and the separated ether extracts were dried over magnesium sulfate. The filtered solvents were removed under reduced pressure and the residue purified by silica gel chromatography (4:1, hexane:ethyl acetate) to give the title compound.

Provenance & Evidence