[F:1][C:2]1[CH:7]=[CH:6][C:5]([C@H:8]([OH:15])[CH2:9][CH2:10][C:11](OC)=[O:12])=[CH:4][C:3]=1[CH3:16]>C(Cl)Cl.C(O)(C(F)(F)F)=O>[F:1][C:2]1[CH:7]=[CH:6][C:5]([C@@H:8]2[O:15][C:11](=[O:12])[CH2:10][CH2:9]2)=[CH:4][C:3]=1[CH3:16]To a solution of (R)-methyl 4-(4-fluoro-3-methyl-phenyl)-4-hydroxy-butanoate (289 mg) in 20 mL DCM was added 4 drops TFA at room temperature and the resulting solution warmed to 40° C. After stirring for 16 h the reaction was cooled to room temperature and concentrated under reduced pressure. The product was isolated by flash column chromatograph eluting with 0% to 30% ethyl acetate/hexane gradient solvent to give 279 mg of (R)-5-(4-fluoro-3-methyl-phenyl)-dihydro-furan-2-one as a colorless oil.
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