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(R)-3-hydroxydihydrofuran-2(3H)-one (2.0 g, 20 mmol) was suspended in Toluene (150 mL) and triphenylphosphine (6.2 g, 24 mmol) and 4-bromo-2-fluoro-5-methylphenol (4.8 g, 24 mmol) were added and cooled to 0° C. The solution was degassed with nitrogen bubble for 10 minutes. Di-tert-butyl diazene-1,2-dicarboxylate (5.4 g, 24 mmol) was dissolved in toluene (40 mL) and added to the reaction over 5 minutes. The reaction was allowed to slowly warm to ambient temperature overnight. The toluene was removed and the oily residue was purified over silica gel (20 to 40% EtOAc in hexanes) to afford (S)-3-(4-bromo-2-fluoro-5-methylphenoxy)dihydrofuran-2(3H)-one (2.9 g, 10 mmol, 51% yield).

1. customThe solution was degassed with nitrogen
2. custombubble for 10 minutes
3. additionadded to the reaction over 5 minutes
4. temperatureto slowly warm to ambient temperature overnight
5. customThe toluene was removed
6. customthe oily residue was purified over silica gel (20 to 40% EtOAc in hexanes)