Quinolizinium nucleophilic additions ring opening

However, in the quinolizinium ion (160) the fused ring increases the stability and makes it more difficult for nucleophilic attack, because now the aromaticity of both rings is lost in the intermediate addition product (161). Conversely, once the addition product is formed, ring opening is particularly easy (162). 

Practically all the reactions of quinolizinium ions are similar to those of pyridinium salts, thus they are resistant to electrophilic attack, but readily undergo nucleophilic addition, the initial adducts undergoing spontaneous electrocyclic ring opening to afford, finally, 2-substituted pyridines however the susceptibility of the cations to nucleophiles is not extreme - Uke simpler pyridinium salts they are stable to boiling water. 

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