Carbon tetrabromide → 2-Ethynyl-1,3,5-tri(propan-2-yl)benzene

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Reaction Steps

To a stirred, degassed solution of triphenylphosphine (21 g, 80 mmol) and carbon tetrabromide (13.3 g, 40 mmol) in dry dichloromethane at 0° C. was added 2,4,6-triisopropylbenzaldehyde (4.64 g, 20 mmol). The resulting mixture was stirred overnight as it was allowed to slowly warm to room temperature. Solids were filtered off, and the volatiles were evacuated under reduced pressure. Pentane was then added, and after extensive trituration the mixture was filtered on a SiO2 plug with pentane as the eluent to afford after evaporation of the solvents the crude intermediate dibromoalkene as a colorless oil that is directly taken to the next step without surther purification. The intermediate is dissolved in dry THF (50 mL), and to the stirred solution cooled to −78° C. is then added nBuLi (2.5M in hexanes, 10 mL) dropwise. The mixture is stirred for 1 hour at −78° C., and let to warm to room temperature for an additional hour. The reaction is quenched by the addition of saturated aqueous NH4Cl, extracted with pentane, and the organic fractions are dried over anhydrous MgSO4. After filtration and evaporation of the solvents, the crude alkyne is purified by filtration on a SiO2 plug with pentane as the eluent. A small crystal of hydroquinone is added to stabilize the product, and the volatiles are evaporated under reduced pressure to afford 9d as a pale pinkish oil (2.63 g, 58% over 2 steps). 1H-NMR (CDCl3, 300 MHz): δ=7.00 (s, 2H), 3.56 (sept, J=6.9 Hz), 3.43 (s, 1H), 2.91 (sept, J=6.9 Hz), 1.28 (d, J=6.9 Hz, 12H), 1.27 (d, J=6.9 Hz, 6H). 13C-NMR (CDCl3, 75 MHz): δ=151.6, 149.7, 122.3, 120.5, 84.5, 81.0, 34.7, 31.8, 24.1, 23.5. Characterization data for 9d are consistent with literature values. (See Knorr, R.; Ruhdorfer, J.; Böhrer, P.; Bronberger, H.; Räpple, E. Liebigs Ann. Chem. 1994, 433-438).

Provenance & Evidence