(1R)-(+)-α-Pinene (25.0 g, 0.183 mol, [α]_D20 +50.9° (neat), 98.6% ee) (Note 1) and 350 mL of dry benzene (Note 2) are placed in a base-washed, 1000-mL Morton flask fitted with a mechanical stirrer, condenser, internal thermometer, and gas inlet. The flask is set in a heating mantle and warmed to 65°C, at which point lead tetraacetate (77.8 g, 0.175 mol) is added via Gooch tubing over 20 min (Note 3). The reaction mixture becomes bright yellow, this color slowly changing to tan after heating at 65°C with stirring for 1 hr. The solution is cooled to room temperature and filtered through a 1-in pad of Celite. The Celite is washed with several 50-mL portions of benzene. To the filtrate is added 300 mL of water, at which point brown-black lead oxide precipitates (Note 4). The two-phase system is swirled vigorously at 10-min intervals for an hour and then filtered through a 1-in pad of Celite. The layers of the filtrate are separated and the aqueous phase is extracted with three 150-mL portions of ether. The combined organic fractions are dried over magnesium sulfate, filtered, and concentrated by rotary evaporation at room temperature to give a mixture of acetates as a colorless liquid (Note 5).

Without purification, the mixture of acetates is placed in a 250-mL, round-bottomed flask and 150 mL of a 10% potassium hydroxide solution in aqueous methanol is introduced at room temperature. After 24 hr of stirring, the brown mixture is poured into a separatory funnel, diluted with 200 mL of water, and extracted with four 150-mL portions of ether. The combined ethereal fractions are dried over anhydrous magnesium sulfate, filtered, and concentrated to give a mixture of alcohols (Note 6) as a light yellow oil.

The mixture of alcohols is placed in a 1000-mL round-bottomed flask, dissolved in 300 mL of ether, and cooled to 0°C. To this solution is added via an addition funnel over a 30-min period a mixture of sodium dichromate dihydrate (27.5 g, 0.092 mol), 100 mL of water, and 10.2 mL of concd sulfuric acid. The mixture is stirred at 0°C for 1 hr, warmed to room temperature where stirring is maintained overnight, diluted with 200 mL of water, and poured into a separatory funnel. The layers are separated and the aqueous phase is extracted with ether (3 × 200 mL). The combined organic layers are washed with saturated sodium bicarbonate solution (200 mL) and brine (200 mL), dried over anhydrous magnesium sulfate, filtered, and concentrated by rotary evaporation to give 16.8–17.8 g (61–65%) of verbenone (Note 7). Final purification is achieved by distillation of the oil through a 5-in Vigreux column at reduced pressure (dry ice-acetone cooled receiver); 13.1 g (47%), bp 108–110°C (5 mm) (Note 8).