合成路线1

2-Chloro-2',4'-difluoroacetophenone (I) was converted to acetate ester (II) by displacement of the chlorine with sodium acetate in the presence of NaI. Subsequent Wittig reaction of (II) with methylenetriphenylphosphorane produced the allyl ester (III), which was hydrolyzed to alcohol (IV) with KOH in aqueous dioxan. Asymmeytric Sharpless epoxidation of (IV) with tert-butyl hydroperoxide in the presence of L-(+)-diethyl tartrate and titanium tetraisopropoxide furnished the (S)-epoxide (V). Ring opening of (V) with the sodium salt of 1,2,4-triazole (VI) gave the triazolyl diol (VII). After conversion of the primary hydroxyl group to tosylate (VIII), ring closure in the presence of NaH generated epoxide (IX). Condensation of (IX) with diethyl malonate afforded a mixture of diastereomeric butyrolactones (Xa, Xb), which was converted to triol (XI) by reduction with lithium borohydride. Treatment of (XI) with p-toluenesulfonyl chloride produced ditosylate (XII). Ring closure of (XII) employing NaH in boiling toluene gave rise to a diastereomeric mixture of tetrahydrofurans, from which the required cis isomer (XIII) was isolated by column chromatography.