Controlled Access to Furanose Precursors Related to Sesquiterpene Lactones. 2

Article abstract of DOI:10.1021/jo00350a063

Compound 1a, whose synthesis is described in the accompanying manuscript, represents the B-C ring system of the eudesmane sesquiterpene lactones.The A ring is represented by the γ-lactone of 1a, and steps for its elaboration include ring expansion and epimerization at C-5.In order to achieve these objectives the lactone was reduced to lactol 3 which showed very little tendency to react as the hydroxy-aldehyde counterpart.However 3 yields N,N-dimethylhydrazone 6a which provides access to the C-5 primary alcohol.This center is eventually epimerized by oxidation to an aldehyde, 8, which is converted to the enol acetate 12 and hydrogenated.The A ring is formed by the intramolecular reaction of a β-keto sulfone and a primary iodide.