Methods are described for the synthesis of 9-hydroxy- and 9-bromopentacyclo[4.3.0.0(2,5),0(3),(8).0(4,7)] nonane (homocubane derivatives) and for the same derivatives of pentacyclo[4.4.0.0(2,5).0(3,8).0(4,7)]decane (basketane). The 9-homocubyl and 9-basketyl radicals generated from these precursors were observed by EPR spectroscopy. In spite of their very large strain energies, both radicals rearranged extremely slowly, and unrearranged products were obtained from homolytic reactions in solution at temperatures below 150 degrees C. At higher temperatures the 9-basketyl radical rearranged by a cascade of three beta-scissions, the ultimate product being 1-(4-cyclobut-2-enyl)cyclohexa-2,4-diene. The Arrhenius parameters for the arrangement were found to be log(A(r)/s(-1)) = 13.6, E(r) = 13.5 kcal mol(-1). The 9-homocubyl radical did not rearrange even at 220 degrees C. An explanation as to why these cage radicals rearrange at least 6 orders of magnitude more slowly than the related cubylcarbinyl radical is presented, and semiempirical SCF-MO calculations are reported.