β Scribed by Baldwin, John E.
No coin nor oath required. For personal study only.
The thermal isomerization of vinylcyclopropane to cyclopentene was discovered in 1960 and soon recognized as the simplest known example of w x a 1,3 sigmatropic shift. Experimental observations for the parent rearrangement and for isomerizations shown by substituted systems suggest that diradical transition structures are involved; recent theoretical treatments of the reaction find no minima corresponding to diradical intermediates. The common dichotomy opposing concerted versus diradical and thus necessarily stepwise mechanisms appears inappropriate. The reaction of vinylcyclopropane may involve four energetically concerted paths traversed by different conformational forms of nearly isoenergetic diradical species leading through four isometric diradical transition structures to cyclopentene.
π SIMILAR VOLUMES
## Abstract Donorβacceptorβsubstituted vinylcyclopropanes such as 1a, 3a, 5a, 5b, 7a, 9a, 9b, and 12a smoothly undergo thermal ring enlargement to functionalized cyclopentene derivatives 2, 4, 6, 8, 10, and 13 at relatively low temperatures (150β190Β°C) in good yields. This vinylcyclopropaneβcyclope
The gas phase isomerization of 1,l -dimethyl-2-vinylcyclopropane to cis-2-methylhexa-1,4-diene has been studied in a static system. The isomerization is homogeneous and kinetically first order. The rate constants were independent of initial reactant pressure in the range 0.6 to 2 torr and of added n