Reaction of the 5-Azoniafulvene Ion with Enamines: A New Approach to Pyrrolizines

The synthesis of N,N-dimethyl-N-[(pyrro-1-yl)methyl]anilinium chloride (14) and of the corresponding p-toluidinium salt 15 is described. These salts, when dissolved in polar solvents, are shown to be in equilibrium with 1-(chloromethyl)pyrrole (17) and thereby potentially with the 5-azoniafulvene ion (2). Consequently, they react under very mild conditions (MeCN, 60°) with enamines to give pyrrolizine derivatives in acceptable yield (40–50°). The process is rationalized in terms of an initial Mannich-type reaction which is immediately followed by acyclization