Rearrangement bicyclooctadienes

Derivatives of 1,2-dihydroazocine are potentially available by valence isomerization of the 7-azabicyclo[4.2.0]octadiene system. Sulfonyl derivatives (71) of the latter have been prepared, but the equilibria with dihydroazocines lie completely on the side of the bicyclic isomers (71JOC435). On heating, the bicyclooctadienes rearrange to the acyclic tetraenes (73), presumably via the unstable dihydroazocines (72). 

Changing the anchoring atom from oxygen to carbon does not change the initial photochemistry of the unsaturated ketones. The rates of the subsequent thermal electrocyclic rearrangements are, however, changed substantially. The tri-fluoroacetyl substituent was chosen to maintain as strong a donor-acceptor interaction in the bicyclooctadienes as possible, as well as to maintain a lowest triplet. 

On the other hand, heating e vo-homonorbornadiene 27 at 90 °C in the presence of RhCl(PPh3)3 yields a mixture of tricyclooctene 29, tetracyclooctane 28, and bicyclooctadiene 30 in a ratio of 62 32 6 (Scheme 2.28) [42]. Formation of the products was explained by assuming a mechanism involving oxidative addition of the cyclopropane and homoallyl-cyclopropylmethyl rearrangement. 

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