36456-22-1Relevant articles and documents
Rearrangement and Cycloreversion of Diels-Alder Adducts of Cyclic 1,3-Dienes to Norbornadienes. A Novel homo-Cope Rearrangement. Evidence for Competitive Pericyclic and Diradical Processes
Hochstrate, Dirk,Klaerner, Frank-Gerrit
, p. 745 - 754 (2007/10/02)
On thermolysis of endo,endo-5, endo,endo-17, and endo,exo-17 ( the endo,endo and endo,exo Diels-Alder adducts of cyclopentadiene 7 or dimethylfulvene 15 to norbornadiene 8 or 7-isopropylidenenorbornadiene 20), a novel type of homo-Cope rearrangement leading to 6, 21, and 23a, respectively, competes with the retro-Diels-Alder reactions.According to a force-field analysis of the kinetic parameters, the competitive reactions (rearrangement and retro-Diels-Alder reaction) of endo,endo-5 occur in a pericyclic fashion whereas in the isopropylidene-substituted systems stepwise processes compete with the corresponding pericyclic reactions.Indirect experimental evidence for this assumption comes from a stereochemical analysis of the retro-Diels-Alder reaction in the cis-5,6-dideuterionorbornene derivatives exo-36-d2, endo-36-d2 and exo-39-d2, endo-39-d2 occuring stereospecifically in the case of exo-36-d2, endo-36-d2 and non-stereospecifically in the case of exo-39-d2, endo-39-d2.The change in mechanism rationalized by a different (allyl vs. pentadienyl) stabilization of the potential diradical intermediates in the stepwise reactions. - Key Words: Kinetic parameters / Stepwise and pericyclic reactions / Calculations, force field / Calculations of transition-state resonance energy (energy of concert)
