To a cooled (-50 °C) solution of lithium hexamethyldisilazide in tetrahydrofuran (1.2 mol/L, 2.3 equiv.) was added dropwise tert-butyl acetate (2.3 equiv.) over 0.5 h, and then the mixture was stirred for 0.5 h. A solution of chlorotriisopropoxytitanium (IV) (2.7 equiv.) dissolved in tetrahydrofuran (5.0 vol) was cooled to 5 °C, which was added dropwise to the reaction mixture over 1 h. After the reaction mixture was stirred at -50 °C for 0.5 h, the compound 2/tetrahydrofuran solution from Step 1A was added dropwise to the reaction mixture over 1 h. After stirring at -50 °C for 0.5 h, the reaction mixture was added dropwise to a solution of citric acid monohydrate (4.0 wt) dissolved in water (11 vol) at 0 °C. After separation of the aqueous layer, the obtained organic solution was washed with 5% sodium bicarbonate aqueous solution and concentrated under reduced pressure to 4.5 vol. After adding 2-methyltetrahydrofuran, the mixture was washed with 2.5% sodium chloride aqueous solution. By repeatedly concentrating with methanol multiple times, the solvent is replaced with methanol. The mixture was filtrated through activated carbon. The activated carbon was washed with methanol. The mixed filtrate was concentrated to 5.0 vol under reduced pressure to obtain a compound 3/methanol solution.