[F:1][C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][C:3]=1[C:8]1[CH:13]=[CH:12][C:11]([CH:14]([S:16]([CH2:18][C:19]([OH:21])=[O:20])=[O:17])[CH3:15])=[CH:10][CH:9]=1.[C:22]1(C)C=CC(S(O)(=O)=O)=CC=1.O>CO.COC(OC)(C)C>[CH3:22][O:20][C:19](=[O:21])[CH2:18][S:16]([CH:14]([C:11]1[CH:12]=[CH:13][C:8]([C:3]2[CH:4]=[CH:5][CH:6]=[CH:7][C:2]=2[F:1])=[CH:9][CH:10]=1)[CH3:15])=[O:17]1.5 gm (50 millimols) of [1-(2'-fluoro-4-biphenylyl)-ethylsulfinyl]-acetic acid, m.p. 164°-165° C., were dissovled in 3 ml of methanol and 1.2 ml of 2,2-dimethoxypropane, 100 mgm of p-toluenesulfonic acid were added to the solution, and the mixture was allowed to stand for 12 days at room temperature. Then, water was added and the ester was extracted with toluene. The organic extract was washed with water, dried and evaporated, and the residue was purified by chromatography on 75 gm of silicagel (grain size 0.05-0.2 mm) with cyclohexane/ethyl acetate--1/4. The combined ester--containing fractions were evaporated, and the residue was recrystallized from 3 ml of isopropanol. Yield: 800 mgm (50% of theory); m.p. 77°-79° C.
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