A. 2-Methyl-2-(3-oxobutyl)-1,3-cyclohexanedione. A 1-L, round-bottomed flask equipped with a thermometer and a reflux condenser capped with an argon-inlet tube is charged with 126.1 g (1 mol) of 2-methyl-1,3-cyclohexanedione (Note 1) and 300 mL of distilled water. To the well-stirred suspension are added 3 mL of acetic acid, 1.1 g of hydroquinone, and 142 g (167 mL, 2 mol) of freshly distilled methyl vinyl ketone (Note 2). The reaction mixture is stirred under argon at 72–75°C for 1 hr, cooled to room temperature, treated with sodium chloride (103 g), and poured into a separatory funnel containing ethyl acetate (400 mL). The organic phase is collected and the aqueous phase is reextracted twice with ethyl acetate (150 mL each time). The combined extracts are washed with two 200-mL portions of saturated brine, dried over anhydrous magnesium sulfate, and filtered, and the filtrate is evaporated at 40°C under reduced pressure (water aspirator) on a rotary evaporator. The residue is kept under high vacuum (1.0 mm) at 40°C for 30 min to give 210.8 g of crude 2-methyl-2-(3-oxobutyl)-1,3-cyclohexanedione (1, "trione") as a pale-yellow oil, homogeneous by thin-layer chromatography (Note 3). This crude material is used in Step B.

B. (S)-8a-Methyl-3,4,8,8a-tetrahydro-1,6(2H, 7H)-naphthalenedione (3-S). A 3-L, one-necked, round-bottomed flask, equipped with an argon-inlet tube and containing a magnetic stirrer, is charged with 5.75 g (0.05 mol) of finely ground L-proline (Note 4) and a solution of 210.8 g of crude trione 1 (from Step A) in 1 L of anhydrous dimethyl sulfoxide (Note 5). The mixture is stirred at room temperature (ca. 25°C) under argon for 120 hr, the magnetic bar is removed, and the solvent is removed under high vacuum (1.0 mm) at 65°C (Note 6) on a rotary evaporator to give 206.9 g of a dark reddish-violet oil. The oil is dissolved in toluene (100 mL) and is absorbed on a column (9 cm X 60 cm) of silica gel (1.5 kg, 70–230 mesh) (Note 7), which was previously packed in hexane. Elution is carried out under a slight positive pressure of argon (ca. 1 atm) (Note 8) initially with 1 L of hexane: ethyl acetate (5 : 1) and then with a 3 : 2 mixture of hexane : ethyl acetate taking 300-mL fractions. The progress of the purification is monitored by thin-layer chromatography (Note 9): no product is observed until ca. 5 L of eluant is collected. Fractions containing the product are combined, and the solvents are removed under reduced pressure (water aspirator) at 45–50°C. The residue is then kept under high vacuum (0.1 mm) at 40°C for 30 min to give 154.2 g of an orange-colored oil, which became glassy and sometimes crystalline on standing at room temperature, [α]_D25 + 68° (toluene, c 1.5) (Note 10). This material is dissolved in 535 mL of ether and is filtered through a fluted filter paper to remove small particles. The flask is rinsed with 500 mL of ether, and this is passed through the filter paper. After cooling to 3°C, the combined filtrates are seeded with a few crystals of pure 3-S (Note 11), and the mixture is left undisturbed at −20°C for 18 hr. Most of the supernatant liquid is carefully decanted without agitation, and the crystals are collected by filtration. The flask is rinsed with cold (0°C) 50% ether in hexane and the rinse is used to wash the crystals. The crystals are dried for 16 hr under high vacuum at room temperature to yield 85.9 g of (S)-enedione (first crop), mp 49–50°C, [α]_D25 + 96.9° (toluene, c 1.2). The combined filtrate and washings are evaporated to give 67.1 g of an orange-colored oil, which is dissolved in 604 mL of ether, cooled to 3°C, and seeded with (R,S)-enedione (Note 12). The mixture is left at −20°C for 18 hr, and the supernatant liquid is carefully decanted (no agitation). The wet crystals are then collected by filtration, washed with cold (0°C) 50% ether in hexane, and dried under reduced pressure at room temperature to give 36.3 g of racemic material (3R + 3S). The filtrate and washing are evaporated to give 30.6 g of an oil, which is dissolved in 100 mL of ether, and filtered through a fluted filter paper. The flask is rinsed with 114 mL of ether, and filtered through the fluted filter paper, and the combined filtrates are cooled to 3°C and seeded with crystals of the pure 3-S. The mixture is left at −20°C overnight, the supernatant liquid is carefully decanted without much agitation and the wet crystals are collected by filtration and washed with cold (0°C) 50% hexane in ether. After drying 15.3 g of light amber-colored crystals (second crop), (mp 49–50°C, (or [α]_D25 + 97.3° (toluene, c 1.0). The total yield of (S)-enedione is 101.2 g (56.8%) (Note 13).