The degenerate vinylcyclopropane rearrangement



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The synthesis of several vinyl cyclopropanes stereospecifically labelled with deuterium is presented. Several new tetrahalovinyl cyclopropanes and tri halovinyl cyclopropanes, which are used as precursors to some of the deuterium labelled vinyl cyclopropanes, are also synthesized. Structure proofs of the deuterated and halogenated vinylcyclopropanes are accomplished by chemical and physical methods, with considerable emphasis being placed on detailed analysis of the 100 MHz nuclear magnetic resonance spectra. Pyrolysis of trans-1-deuterio-2-vinylcyclopropane shows that the reversible, geometrical cis-trans isomerization of the cyclopropyl ring is ca. 40 times faster than the irreversible formation of cyclopentene-d-j at 325[degrees]C. The Arrhenius Equation derived from the kinetic studies of deuterium epimerization on the cyclopropyl ring is: k = 10[raised 14.5[plus-minus]0.1] exp(-48,200[plus-minus]l,600/RT). Interpretation of the time history of the thermolysis of 1 -(cis- and trans-2-deuteriovinyl)-trans,trans-2,3-dideuteriocyclopropane shows unequivocally that the reaction does not follow any simple concerted pathway, but is best described by an intermediate diradical.