合成路线1

Horner-Emmons reaction of 4-(methylthio)benzaldehyde (XI) with phosphonate (XII) in the presence of Et3N and MgBr2 afforded unsaturated ester (XIII). Oxidation to sulfone (XIV) was effected with H2O2 and a catalytic amount of Na2WO4. Subsequent reduction of the ester group with DIBAL-H in CH2Cl2 at -78 C produced allyl alcohol (XV), which was converted to iodide (XVI) on treatment with I2, Ph3P and imidazole in acetonitrile. Reaction of this iodide with methyl chlorodifluoro-acetate in the presence of KF and CuI in DMF at 90 C yielded trifluoromethyl compound (XVIII). Alternatively, alcohol (XV) could be converted to (XVIII) with chlorodifluoroacetic anhydride followed by conversion of the intermediate ester (XVII) to trifluoroethyl compound in the presence of KF and CuI. Sharpless asymmetric dihydroxylation of olefin (XVIII) with potassium ferricyanide or iodine and a catalytic amount of K3OsO4 as the oxidants and the chiral ligand hydroquinidine 1,4-phthalazinediyl diether ((DHQD)2PHAL) yielded diol (XXI) with a 79% e.e. In a related procedure, diol (XXI) was obtained by reduction of ester (XIII) and treatment of the resulting allyl alcohol (XIX) with chlordifluoroacetic anhydride to give olefin (XX). Sharpless oxidation of (XX) then produced a mixture of diols with a sulfide, sulfoxide and sulfone groups, which was oxidized with H2O2 and Na2WO4 to the sulfone (XXI) with a 82% e.e. Recrystallization from isopropyl acetate-hexane raised the e.e. to > 98%. Then, Swern oxidation of diol (XXI) provided hydroxyketone (VII). Subsequent esterification with 3,4-difluorophenoxyacetic acid (XXII) in the presence of CMC and DMAP gave ester (X), which was cyclized to the target furanone by treatment with DBU using isopropyl trifluoroacetate as a water scavenger.