Synthesis of heliannuols A and K, allelochemicals from cultivar sunflowers and the marine metabolite helianane, unusual sesquiterpenes containing a benzoxocane ring system

Synthesis of the allelochemicals heliannuols A and K, and the sesquiterpene helianane is described. A regioselective cleavage of a benzo-fused oxabicyclo(5.1.0)octane system under hydrogenation as well as radical induced condition was developed to generate the basic benzoxocane ring system of these unusual sesquiterpenes.