Concise Syntheses of (−)- and (+)-Syringolide 1 and (−)-Δ7-Syringolide 1

(−)- and (+)-Syringolide 1 have been synthesized from 2,3-O-isopropylidene-β-threo-pentulofuranose (1), which was readily prepared from d- or l-xylose, respectively. Condensation of 1 with 3-oxooctanoic acid and treatment of the ester with TFA:H2O (9:1) produced syringolide 1 in 6.3% yield for the two steps. According to the same synthetic route by replacing 3-oxooctanoic acid with 3-oxo-7-octenoic acid, (−)-Δ7-syringolide 1 was prepared in 5.8% yield. Primary β-keto esters of arabinulose and fructose were also prepared to test the selectivity of the biomimetic cyclization to form syringolide analogs.