Heliannuols A-K are the sesquiterpenes isolated from the Spanish cultivated sunflower Helianthus annuus L. cv. SH-222. They exhibited bioactivities as phytotoxic allelochemicals and are potential sources of new type herbicides with new modes of action, which may be less harmful than herbicides presently used in agriculture. The enantioselective synthesis of heliannuol E has already been reported by Shishido, although its bioactivity has uncovered. In addition to such a background, the chroman framework of this molecule would be an attractive synthetic target of the anodic oxidation-ring expansion protocol developed by our group. Electrolysis might be one of powerful tools for organic synthesis, because electron transfer reactions can be conducted under high cost-performance and safety conditions, without toxic reagents. We present our investigation process. Thus, anodic oxidation of halogenated phenol derivatives(1, 5) provided the corresponding spiro compounds(2, 6), which on treatment with a Lewis acid gave the chroman derivatives (3, 4, 7, 8), By employing this key reactions, (8R,10S)- and (8R,10R)-heliannuol E. have been synthesized. Comparison of their spectral data and optical rotations revealed that the natural (-)-heliannuol E has the latter absolute configuration. In addition application of our synthetic methodology to other heliannuols, allolopathogenic assessment of heliannuols and related compounds would be presented.
