Tetrabutylammonium chloride (0.55 g, 1.98 mmol) was added to a solution of (5Z,8Z,11Z,14Z,17Z)-icosa-5,8,11,14,17-pentaen-1-ol, (3.50 g, 12.1 mmol) in toluene (35 mL) at ambient temperature under nitrogen. An aqueous solution of sodium hydroxide (50% (w/w), 11.7 mL) was added under vigorous stirring at room temperature, followed by t-butyl 2-bromobutyrate (5.41 g, 24.3 mmol). The resulting mixture was heated to 50° C. and additional t-butyl 2-bromobutyrate was added after 1.5 hours (2.70 g, 12.1 mmol), 3.5 hours (2.70 g, 12.1 mmol) and 4.5 hours (2.70 g, 12.1 mmol) and stirred for 12 hours in total. After cooling to room temperature, ice water (25 mL) was added and the resulting two phases were separated. The organic phase was washed with a mixture of NaOH (5%) and brine, dried (MgSO4), filtered and concentrated. The residue was purified by flash chromatography on silica gel using increasingly polar mixtures of heptane and ethyl acetate (100:0→95:5) as eluent. Concentration of the appropriate fractions afforded 1.87 g (36% yield) of the title compound as an oil. 1H NMR (300 MHz, CDCl3): δ 0.85-1.10 (m, 6H), 1.35-1.54 (m, 11H), 1.53-1.87 (m, 4H), 1.96-2.26 (m, 4H), 2.70-3.02 (m, 8H), 3.31 (dt, 1H), 3.51-3.67 (m, 2H), 5.10-5.58 (m, 10H).
