UBC Theses and Dissertations
Thermolysis of unsymmetrically substituted vinylcyclopropane systems : site-selectivity in homo-[1,5]-sigmatropic hydrogen migrations Maxwell, Anderson Richard
This thesis describes the preparation and thermal rearrangement, via homo-[l,5]-hydrogen migration, of a series of unsymmetrically substituted bicyclic and tricyclic vinylcyclo-propanes (65a)-(67a), (68b), (69), (70), (71a), (72a), (74)-(76) and (77a). In each of these compounds two hydrogen atoms one (H[sub=C]) adjacent to the substituent and the other (H[sub=J]) more distant from it - are suitably disposed to undergo homo-[1,5]-hydrogen migration. It was found that an oxygen substituent retarded the rate of homo-[l,5]-migration of the hydrogen atom (H[sub=C]) adjacent to it relative to that of the other more remote hydrogen atom (H[sub=J]) The retarding effect appeared to be dependent on the structure of the oxy-substituted vinylcyclopropane as well as on the nature of the oxygen substituent. A methyl substituent exerted a negligible, retarding effect on the rate of migration of while phenyl and trimethylsilyl groups accelerated the rate of migration of H[sub=C] relative to that of H[sub=J]. The results are consistent with the proposal that in the transition state for the homo-[1,5]-hydrogen migration the carbon centre bearing the migrating hydrogen atom develops a partial negative charge.
Item Citations and Data