To a solution of (2Z,4E,6E)-2,6-difluoro-7-(3-methoxymethoxy-5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-naphthalen-2-yl)-3-methyl-nona-2,4,6-trienoic acid ethyl ester (Compound 19, 2-E/Z mixture, 387 mg, 0.81 mmol) in i-PrOH (2 mL) and THF (2 mL) was added conc. HCl (1.0 mL). The mixture was stirred at ambient temperature for overnight, extracted with EtOAc (×3). The combined organic layer was washed with brine, dried over Na2SO4, and concentrated in vacuo. The residue was purified by flash column chromatography on silica gel (5% EtOAc-hexane) to give the title compound as a 2-E/Z mixture (370 mg, 100%). This mixture was used directly for the next alkylation reaction.
