Cope reaction families: to be or not to be a biradical.
The cyclization reactions of polyunsaturated systems such as enediynes, enyne-allenes, as well as many others, can be structurally related to the Cope reaction and grouped into two branches: 6pi (e.g., Cope, allenyl-Cope) and [2sigma + 4pi] systems (e.g., Bergman, Myers-Saito). After extensive computional (BCCD(T)/cc-pVDZ//UBLYP/6-31G) examination of a large set of Cope-related reactions, we derive the following simple rule: biradical intermediates are involved along the reaction path if they are stabilized by allylic resonance or aromaticity.
Institute of Organic Chemistry, Justus-Liebig-University, Heinrich-Buff-Ring 58, D-35392 Giessen, Germany.
Armando
A
Navarro-Vázquez
Matthias
M
Prall
Peter R
PR
Schreiner