An Annelation Approach to the Synthesis of Eudesmane and Elemane Sesquiterpene Lactones. Total Synthesis of dl-Dihydrocallitrisin, dl-7,8-Epialantolactone, dl-7,8-Epiisoalantolactone, and dl-Atractylon

Article abstract of DOI:10.1021/ja00527a046

An annelation approach to the synthesis of eudesmane sesquiterpenes is described.The 1,6-annelation reagent α-carbomethoxy-β-methyl-γ-methylidene-Δ^α,β-butenolide (1) is used to construct the linear tricyclic lactone 2,5,6,7,8,8a,9,9aβ-octahydro-8aβ-methyl-2-oxonaphtho<2,3-b>furan-3-carboxylic acid methyl ester (2).The conversion of 2 to dl-dihydrocallitrisin (3), dl-7,8-epialantolactone (4), dl-7,8-epiisoalantolactone (5), and dl-atractylon (6) is detailed.Studies directed toward synthesis of the elemane sesquiterpene lactones vernomenin and vernolepin also are presented.