# Mechanism for synthesising azetidine

Problem
A synthesis of azetidine is shown below. Provide a mechanism for all the steps. Why does the formation of azetidine in the last step require high temperature?

My working is thus:

I am stuck on the last step and my version seems wrong. Can someone please guide me in the right direction?

• You lost a carbon atom on the last step of your first image (but no harm done, because you regenerated it from scratch at the beginning of the second). – Jan Nov 4 '15 at 9:57

It’s not really a point. It’s just that the reaction conditions contain $\ce{HCl}$ which will protonate any strong enough base around and the secondary amine is a strong enough base. It’s more of a consequence of the reaction conditions than an actual pointful step.