Enantioselective synthesis of heliannuol E; structural consideration of natural molecule

Heliannuol E 1, isolated from Helianthus annuus L. cv. SH-222, was successfully synthesized in both optically active forms, by novel ring-expansion reaction of the corresponding spirodienone derivatives 8 and 17, which were produced from 7 and 16 under anodic oxidation conditions. The absolute structure of the natural product was determined to have R-configuration at the benzylic position.