Reaction of di-tert-butylcyclopentadiene with excess potassium tert-bu
toxide in the presence of elemental selenium leads to cyclopentadienes
bridged by two or three selenium atoms through one or two diselenoket
al functionalities. opentane-1,2'-cyclopenta[b][1,3]diselena-2,4-diene
(1) and o-3a,7a-epi-selenodicyclopenta[b,e][1,4]diselenine (2) have b
een characterized by single-crystal X-ray diffraction.