Water → (4S)-4-benzyl-3-[(2E)-4,4,4-trifluoro-3-methyl-but-2-enoyl]-1,3-oxazolidin-2-one

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(4S)-4-Benzyl-1,3-oxazolidin-2-one (828 g, 4.67 moles) was dissolved in 6.8 L THF and cool to −40 to −50° C. To the solution of (4S)-4-benzyl-1,3-oxazolidin-2-one, 2.5 M BuLi in hexanes (1302 g, 1880 mL, 4.70 mole, 1.01 equivalents) was added while keeping the temperature at <−40° C. To the cold solution of the Li salt of (4S)-4-benzyl-1,3-oxazolidin-2-one, 4,4,4-trifluoro-3-methyl-2-butenoic acid chloride (887 g, 5.14 moles, 1.1 equivalents) was added over 10-30 minutes, all-owing the temperature to rise and wash in with 0.4 L THF. The reaction was warmed to 20-25° C. and stirred for 2 h. 0.9 L water was added and stirred for 16 h. The THF was distilled off with a bath temperature of 35° C. and vacuum<40 mm Hg. Toluene (5.8 L) was added and the phases split. 4-L saturated NaHCO3 was used to wash (2×), the mixture was filtered through Celite and the phases split. 2.5-L water (2×) was used as a wash and the toluene layer was filtered through Celite. The remaining water was removed. The toluene was distilled off with a bath temperature of 40° C. and vacuum<40 mm Hg. At the end of the distillation the product started to crystallize with a pot temperature of 30° C. Distillation is continued to a pot temperature of 35° C. giving a solid mobile mass of 1456 g. The solid is dissolved in 2.9 L (2 vol) EtOH (99.5% EtOH:0.5% toluene). While stirring at 20-25° C., water (1.09 L, 0.75 vol) was added over 1 h forming crystals. Stirring is continued for 16 h at 15-25° C., followed by cooling to 0-5° C. and holding for 1 h. The crystals are filtered, washed with filtrate and dried at 50° C. for 16 h giving 1229 g, 84% of (4S)-4-benzyl-3-[(2E)-4,4,4-trifluoro-3-methyl-but-2-enoyl]-1,3-oxazolidin-2-one.

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