By pyrolysis over 140°C, several 2-alkenyloxytropones gave terminal dienes and regenerated tropolones. The elimination proceeded in the electrocyclic 6π+2σ+2σ-mode on the Claisen intermediates. This was applied to a synthesis of thujopsadiene.
The kinetic features of the [1,9] sigmatropy (with 2-benzyloxy-3-bromotropone) and the [3,3] sigmatropy (with 2-allyloxytropone and 2-[(3-methyl-2-butenyl)oxy]tropone) were investigated under various pressures (1 to 1600 bar). The activation volume of [1,9] sigmatropy was of the same order as those of [1,5] sigmatropy of cyclopentadienes. The activation volume of [3,3] sigmatropy of more sterically-hindered