Antarafacial rearrangements

Baldwin and Patrick have demonstrated by the experiment outlined in Equation 12.97 that the concerted [2,3]-rearrangement takes the suprafacial path over the allyl group.157 The two products arise from the two conformations 77 and 78 antarafacial rearrangement would have yielded 79 and 80, which were not found. 

Sigmatropic hydrogen migrations involve four pairs of electrons. They can take place under thermal conditions because the eight-membered-ring transition state allows the required antarafacial rearrangement. 

Does the [1,7] sigmatropic rearrangement that converts provitamin D3 to vitamin D3 involve suprafacial or antarafacial rearrangement ... 

Migration from one face to the other face is an antarafacial rearrangement. 

The HOMO of an allyl radical is antisymmetric. A [1,3] sigmatropic rearrangement cannot occur in a suprafacial process. An antarafacial rearrangement is symmetry allowed, but cannot occur because of geometric restrictions. 

A crystal-structure determination reveals a trihapto allyl co-ordination for the dienyl ligand in (cod)Rh(j -cyclo-octadienyl), giving the Rh a 16 electron configuration. The i -benzyl complex (38) has been prepared. Styrene dissociation occurs in solution, and while an exchange process results in equivalence of the two ortho protons, the steric environment at the ben2yl carbon remains constant. This is shown to occur by a selective antarafacial rearrangement via an -benzyl intermediate. ... 

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