Three new triketone–sesquiterpene adducts, myrtucomvalones A–C (1–3), along with four known compounds (4–7) were isolated from the leaves of Myrtus communis ‘Variegata’. Compounds 1 and 2 are the first examples of triketone–cubebane hybrids with an unusual carbon skeleton. Their structures with absolute configurations were determined by spectroscopic data, single crystal X-ray diffraction and electronic circular dichroism (ECD) analyses. Compounds 1–7 displayed inhibitory activities against respiratory syncytial virus (RSV).