DYOTROPIC HYDROGEN-TRANSFER IN DIHYDROSES QUIBICYCLO[2.2.2]OCTENE ANDIN DIHYDRO-SYN-SESTERBICYCLO[2.2.2]OCTENE

The intramolecular dyotropic hydrogen transfer is studied in dihydrose squibicyclo[2.2.2]octenes. In the parent system 4-d(2) the process tra nsfers two hydrogen atoms from the ethano to the etheno bridge; it is thermoneutral and reversible at 200 degrees C. In 12a, b a 1,2-dihydro benzene acts as the hydrogen donor; the reaction is highly exothermic and occurs already at room temperature. In 19-d(4) the dyotropic hydro gen exchange from a 1,2-dihydrobenzene to benzene is again thermoneutr al and occurs at 200 degrees C. The kinetic parameters of these reacti ons, Listed in Table 7, indicate a concerted pericyclic pathway. In th e extended dihydro-syn-sesterbicyclo[2.2.2]octenes 6-d(2) and 15a, b t wo hydrogen transfers occur in sequence, the central bridge serving as a relais. Here the dyotropic processes establish equilibria between s tructures with stacked and isolated double bonds, allowing an evaluati on of the van der Waals interaction in the former. It is found that th is interaction changes with the type of the stakked pi-systems from re pulsive in 6-d(2) to slightly attractive in 16a (see Table 8).