Hi everyone,

I have a homework in organic chemistry and I really don't know how to do it so I would be delighted to have your help
Here is the exercise :

The synthesis of aspartame is carried out according to the following scheme:

In a first step, the action of methanol in the presence of hydrogen chloride (HCl) gives compound A in which a single carboxylic acid function has been esterified.

This compound A is then reacted with phosgene (COCl2) to give the cyclic product noted B.

Propose a mechanism for this transformation from A to B, knowing that phosgene can be considered in this reaction as a double acid chloride (Cl-C(O)-Cl). 

What have you done so far / where are you stuck?

It is often helpful to think in terms of nucleophiles and leaving groups.