The metal-promoted [6+4] cycloaddition using a tropone-metal complex is a stepwise, photolytic process that lacks the periselectivity issues of the purely thermal [6+4] cycloaddition.
Although notable work on [6+4] cycloadditions was reported by Rigby et al. in the late 1980s, the study of metal-complexed dienes with tropones received comparatively little attention.