Sequential 1,4- and 1,2-addition reactions to α,β-unsaturated N-acyliminium ions: a new strategy for the synthesis of spiro and bridged heterocycles.

Novel bicyclic and tetracyclic spirocycles and tricyclic bridged heterocyclic systems can be readily prepared from sequential 1,4- and 1,2-addition reactions of latent bis-nucleophiles to α,β-unsaturated N-acyliminium ions.