“…Aziridinium ions are known to undergo regioselective ring-opening with a wide range of nucleophiles, and this type of rearrangement has been used extensively to make planar nitrogen-containing heterocycles. , In 1970, Arata reported the synthesis of bridged lactam 225 , containing a [4.4.1] ring system via aziridinium rearrangement using a one-pot protocol (Scheme ). , The proposed mechanism is outlined in Scheme , and it involves the following steps: (1) tautomerization of enamine 224 to iminium ion, (2) addition of the trichloromethyl moiety, (3) formation of the aziridinium 224b , (4) regioselective nucleophilic ring-opening to the trichloroderivative 224c , and (5) hydrolysis to give the bridged lactam 225 . Subsequently, Miyano and co-workers studied a related rearrangement in the 1-azabicyclo[3.3.1]nonane system (Scheme ). , In their case, the reaction was carried out stepwise and the trichloromethyl analogue 227 was isolated . This intermediate then underwent rearrangement to 1-azabicyclo[3.3.1]nonane 229 upon heating in pyridine.…”