Claisen Rearrangement of Allyl Phenyl Ether. 1-14C and β-14C Kinetic Isotope Effects. A Clearer View of the Transition Structure

Article abstract of DOI:10.1021/ja00035a042

The kinetic isotope effects, k 12C/k 14C, for the rearrangements of allyl <1-14C>phenyl ether and <β-14C>allyl phenyl ether have been measured: 1.0119+/-0.0009 and 1.0148+/-0.0005, respectively.These results, along with those reported earlier for 18O, 2-14C, ?-14C, and γ-14C, represent the first complete kinetic isotope effect (KIE) description of a pericyclic system.Modeling calculations have been applied to the haevy-atom KIE and the previously reported deuterium KIE to define the transition structure of the rearrangement more explicitly.The calculations confirm our earlier description that the C_α-O bond is 50-60percent broken while the C_γ-C_ortho bond is 10-20percent formed and now provide significantly more insight to the dynamics of the rearrangement.Coupling between the phenoxy and allyl fragments is stronger, and within the fragments is weaker, than previously supposed.