合成路线1

The resulting diol (VIII) was converted to the isopropylidene ketal (X) by means of dimethoxypropane (IX) and camphorsulfonic acid. Both pivaloyl groups of (X) were reductively removed with LiAlH4, and then selective protection of the primary hydroxyl group gave monopivalate (XI). The secondary hydroxyl group of (XI) was further oxidized to ketone (XII) with PCC. Aldol condensation of (XII) with 3-methyl-2-butanone (XIII) in the presence of LDA afforded (XIV) as a 3:7 diastereomeric mixture. Hydrolysis of pivalate ester of (XIV) with NaOMe was accompanied by intramolecular cyclization to the tetrahydrofuran (XV). This unstable intermediate was dehydrated with warm aqueous AcOH to produce furan (XVI) along with a minor amount of the ketal-hydrolyzed analogue. A trimethylsilyl group was introduced at position 5 of the furan ring of (XVI) through lithiation with n-BuLi, followed by treatment with trimethylsilyl chloride yielding (XVII).