Synthesis of helianane, an unusual marine sesquiterpene employing ring-expansion by flash vacuum thermolysis

Abstract

A total synthesis of the marine sesquiterpene helianane 1 is described involving the thermal rearrangement of the benzoxabicyclo[4.2.0]octenone 4 to generate the dienone 5 incorporating the benzoxocane ring system of 1 . This dienone was converted to the key ketone 11 , which on interaction with methylmagnesium iodide followed by hydrogenation of the resulting alkene 18 furnished helianane 1 .