The preparation of 4-isopropylpyridine is as follows:
1) At 0 °C, 11.0 mL of n-BuLi (1.6 M hexane solution) was added dropwise over 20 minutes to a mixture of 5.1 g (14.3 mmol) Ph3PhCH3Br in 25 mL THF under stirring. After 1 hour, 1.5 g (12.8 mmol) of 1-(pyridin-4-yl)acetone was added to 20 mL of THF. The mixture was stirred at 0 °C for 1 hour, and then stirred at room temperature for 50 minutes. The mixture was filtered through a Buchner funnel. Saturated NH4Cl and H2O were added to separate the layers. The organic layer was washed with brine, dried with Na2SO4, filtered, and concentrated. Purification by rapid silica gel chromatography (54% EtOAc/hexane) yielded isopropylpyridine as a pale yellow liquid. 2) At room temperature, a mixture of 4-(prop-1-en-2-yl)pyridine and 342 mg of 20% Pd(OH)₂ in 15 mL of LEtOAc and 10 mL of MeOH was stirred under an H₂ balloon. After 24 hours, 305 mg of 20% Pd(OH)₂ was added. After 6 hours, the mixture was filtered through diatomaceous earth, and the solution was concentrated. The crude product was dissolved in 15 mL of MeOH, and 512 mg of 20% Pd(OH)₂ was added. The mixture was stirred under an H₂ balloon at room temperature for 11.5 hours, filtered through diatomaceous earth, and concentrated to obtain 4-isopropylpyridine.
