To a mixture of diarachidonyl methanol (IV, 0.41 g, 0.71 mmol) and anhydrous potassium carbonate (0.05 g) in 10 mL of CH2Cl2 was added pyridinium chlorochromate (PCC, 0.50 g, 2.3 mmol). The resulting suspension was stirred at room temperature for 90 mins. Ether (50 mL) was then added into the mixture, and the resulting brown suspension was filtered through a pad of floresil (30 mL). The pad was further washed with ether (3×30 mL). The ether filtrate and washes were combined. Evaporation of the solvent gave 0.40 g of an oily residual as a crude product. The crude product was purified by column chromatography on silica gel (230-400 mesh, 10 mL) eluted with 0-3% ether in hexanes. This afforded 0.30 g (75%) of diarachidonyl ketone (V). 1H NMR (400 MHz, CDCl3) δ: 5.3-5.5 (16H, m, 8×CH═CH), 2.82 (12H, t, 6×C═C—CH2—C═C), 2.40 (4H, t, 2×CO—CH2), 2.08 (8H, m, 4× allylic CH2), 1.25-1.65 (20H, m), 0.90 (6H, t, 2×CH3) ppm.
