HOMOLYTIC REACTIONS OF HOMOCUBANE AND BASKETANE - REARRANGEMENT OF THE 9-BASKETYL RADICAL BY MULTIPLE BETA-SCISSIONS

Methods are described for the synthesis of 9-hydroxy- and 9-bromopenta cyclo[4.3.0.0(2,5),0(3),(8).0(4,7)] nonane (homocubane derivatives) an d for the same derivatives of pentacyclo[4.4.0.0(2,5).0(3,8).0(4,7)]de cane (basketane). The 9-homocubyl and 9-basketyl radicals generated fr om these precursors were observed by EPR spectroscopy. In spite of the ir very large strain energies, both radicals rearranged extremely slow ly, and unrearranged products were obtained from homolytic reactions i n solution at temperatures below 150 degrees C. At higher temperatures the 9-basketyl radical rearranged by a cascade of three beta-scission s, 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 di d not rearrange even at 220 degrees C. An explanation as to why these cage radicals rearrange at least 6 orders of magnitude more slowly tha n the related cubylcarbinyl radical is presented, and semiempirical SC F-MO calculations are reported.