Dibromomethane → (S)-2-methyl-4-methylidene-3-(2-propynyl)-1-tert-butyldimethylsilyloxycyclopent-2-ene

Participants

Reaction Steps

1H-NMR (solvent: CDCl3, internal standard: TMS) δ value (ppm): 4.69(brd, 1H), 3.11(ABq, 2H), 2.74(dd, 1H), 2.28(dd, 1H), 2.16(s, 3H), 1.96(t, 1H), 0.92(s, 9H), 0.15(s, 3H), 0.12(s, 3H). 2 Dibromomethane (13.04 g) and zinc dust (14.71 g) were added to tetrahydrofuran (120ml), and the resulting mixture was cooled to 0°~5° C. A dichloromethane solution (50 ml) of 1M titanium tetrachloride was added to the tetrahydrofuran solution over about 10 min, and the resulting mixture was allowed to react for 3 days at 0°~5° C. Then a solution of (S)-4-tert-butyldimethylsilyloxy-3-methyl-2-(2-propynyl)cyclopent-2-ene-1-one (13.22 g) in dichloromethane (50 ml) was added at 0°~5° C. over about 10 min. After the reaction was continued for 2 hours at the same temperature, hexane (200 ml) and then a slurry consisting of sodium bicarbonate (75 g) and water (40 ml) were added After stirring for 2 hours at 0°~5° C., the organic layer was separated by decantation. The obtained residue was extracted three times with n-hexane (200 ml). The combined organic layer was washed with saturated aqueous sodium bicarbonate solution, and dried over anhydrous sodium sulfate. The solvent was evaporated under reduced pressure, and the resultant residue was subjected to silica gel column chromatography (eluent; n-hexane: ethyl acetate=50:1) to afford the desired product, (S)-2-methyl-4-methylidene-3-(2-propynyl)-1-tert-butyldimethylsilyloxycyclopent-2-ene (9.02 g, yield 68.7%) as a pale yellow oil.

Provenance & Evidence