The rearrangement of some substituted cyclopropylcarbinyl radicals
The ring-opening of cyclopropylcarbinyl radicals has been postulated to proceed via a dipolar transition state. In this thesis it was hoped to delineate some of the factors that influence the rate of ring-opening of some substituted cyclopropylcarbinyl radicals and hence estimate their relative importance. This would allow the involvement of the dipolar transition state in the ring-opening process to be assessed. In order to achieve the above objective it was necessary to synthesise methylcyclopropanes with substituents at both the a-position and the 2-position. Such compounds should readily react with t-butoxyl radicals to give a series of cyclopropylcarbinyl radicals. The bulk of the synthetic work was in two parts, the first involved synthesis of 2,2-difluoro substituted cyclopropanes, to determine the influence of fluorine substituents in the cyclopropane ring. The second section involved cyclopropanations using carboethoxycarbene. Radicals were generated, from successfully synthesised precursors, and their electron spin resonance spectra recorded. The data obtained provided evidence for the involvement of a dipolar transition state in some of the ring-opening rearrangements. However, in several of the radicals other factors are clearly influencing the observed ring-opening. In another section of the work the effect of phenyl and ferrocenyl substituents on the ring-opening of cyclopropylcarbinyl radicals was assessed.