Dyotrope Wasserstoffübertragung in Dihydrosesqui‐ und in Dihydro‐<i>syn</i>‐sesterbicyclo[2.2.2]octenen

Abstract

Dyotropic Hydrogen Transfer in Dihydrosesqui‐ and in Dihydro‐ syn ‐sesterbicyclo[2.2.2]octenes The intramolecular dyotropic hydrogen transfer is studied in dihydrosesquibicyclo[2.2.2]octenes. In the parent system 4 ‐ d 2 the process transfers two hydrogen atoms from the ethano to the etheno bridge; it is thermoneutral and reversible at 200°C, In 12a, b a 1,2‐dihydrobenzene acts as the hydrogen donor; the reaction is highly exothermic and occurs already at room temperature. In 19 ‐ d 4 the dyotropic hydrogen exchange from a 1,2‐dihydrobenzene to benzene is again thermoneutral and occurs at 200°C. The kinetic parameters of these reactions, listed in Table 7, indicate a concerted pericyclic pathway. In the extended dihydro‐ syn ‐sesterbicyclo[2.2.2]octenes 6 ‐ d 2 and 15a, b two hydrogen transfers occur in sequence, the central bridge serving as a relais. Here the dyotropic processes establish equilibria between structures with stacked and isolated double bonds, allowing an evaluation of the van der Waals interaction in the former. It is found that this interaction changes with the type of the stakked π‐systems from repulsive in 6 ‐ d 2 to slightly attractive in 16a (see Table 8).