Triphenylphosphine (21.0 g, 80 mmol) was dissolved in dry THF (170 mL) at 0° C. under inert atmosphere and added DIAD (15.8 mL, 80 mmol) dropwise. After 40 minutes at 0° C. the white suspension was added dropwise to a solution of (5Z,8Z,11Z,14Z,17Z)-icosa-5,8,11,14,17-pentaen-1-ol (11.5 g, 40 mmol) and thioacetic acid (5.7 mL, 80 mmol) in dry THF (50 mL) during 15 minutes. The resulting turbid mixture was stirred at 0° C. for 30 minutes, followed by ambient temperature for 1.5 hour. Heptane was added (200 mL), the mixture was stirred for ten minutes and the precipitated white solid removed by filtration and rinsed with heptane (150 mL). The residue was concentrated to remove most of the THF and stirred at ambient for 18 hours. The mixture was filtered, concentrated and added heptane (200 mL). The resulting mixture was stirred for 2 hours, filtered and evaporated. The residue was purified by flash chromatography on silica gel, using EtOAc:Heptane (2:98), followed by EtOAc:Heptane (4:96) and finally EtOAc:Heptane (5:95). Concentration of the appropriate fractions provided 11.0 g (79% yield) of the title compound as oil.
