[1,3]-sigmatropic rearrangements of divinylcyclopropane derivatives and hetero analogs in competition with Cope-type rearrangements - A DFT study

Two possible types of competing [1,3] rearrangements of divinylcyclopropane derivatives and of the hetero-analogous compounds vinylcyclopropanecarbald ehyde and vinylcyclopropanecarbthioaldehyde to five-membered ring compounds have been investigated theoretically by (U)DFT (Becke3LYP/6-31G*) methodol ogy. Although both of the rearrangement pathways correspond to a reaction o f the monosubstituted cyclopropane substructure, i.e. a reaction of vinylcy clopropane or of cyclopropanecarb (thio) aldehyde, new features in the reac tivity are seen due to the combination of two substituents. Reaction parame ters such as reaction and activation energies of the [1,3]-sigmatropic rear rangements have been calculated and compared. Substituent effects of hydrox y and formyl (donor and acceptor) groups in specific positions have also be en considered. On the basis of these calculations, the [1,3] rearrangement of vinylcyclopropanecarbaldehydes to dihydrofurans can be expected to be ki netically favored over their conversion to cyclopentenes, while formation o f the latter should be favored thermodynamically. This prediction is borne out by the experimental findings. Depending on the substitution pattern, th e [1,3]-sigmatropic rearrangement of vinylcyclopropanecarbaldehydes may com pete with the [3,3]sigmatropic rearrangement. For the other investigated st ructures, the [1,3] rearrangement is strongly disfavored.