Approaches to bicyclic ring systems via 1,5 allylic abstraction cyclisation

A new 1, 5 allylic abstraction, cyclisation sequence has been developed and applied to the synthesis of fused bicyclic systems. Initial studies directed towards the synthesis of the bicyclo[3.3.0] octane skeleton are described: vinyl bromide 4 was subjected to standard cyclisation conditions to give 5 as a single isomer. Further studies were directly related to the development of the rearrangement sequence: vinyl bromide 10 was subjected to cyclisation conditions to give 12 in moderate yield. A significant improvement in the rate and efficiency of this type of conversion was achieved by introducing an electron withdrawing group on the acceptor alkene, thus compound 17 gives 18 in excellent yield.