Transition structures and energetics for the Cope rearrangements of cis-1,2-divinylcyclobutane, obtained by RHF/6-31G* and MP2(full)/6-31G*//RHF/6-31G* calculations, are reported. Three transition structures (endo-boatlike, chairlike and exo-boatlike) have been located, giving rise to formation of cis,cis-, cis,trans- and trans,trans- 1,5-cyclooctadienes, respectively. cis-1,2-divinylcyclobutane rearranges via an endo-boatlike transition structure and yields the corresponding cis,cis product with higher exothermicity. Formation of severely strained cis,trans- and trans,trans-1,5-cyclooctadienes from this rearrangement is also discussed. (C) 2003 Elsevier Science B.V. All rights reserved.