Question: The problem is such:

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> [![Question asking to sketch the correct mechanism for the given reaction pathway](https://i.stack.imgur.com/qB7rY.png)](https://i.stack.imgur.com/qB7rY.png)
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So far my working has been:

[![proposed reaction mechanism](https://i.stack.imgur.com/2l725.jpg)](https://i.stack.imgur.com/2l725.jpg)

I'm concerned about the last step where the ester forms a ring. The methyl group doesn't look like a plausible leaving group, but it does not appear in the product so how can I get rid of it?

Answer: 
A methyl cation definitely won’t leave by itself. However, you can consider bromide ions floating around in solution. These bromide, being nucleophilic can attack the methyl group in an $\mathrm{S\_N2}$ manner, because any positively charged oxygen is a good leaving group. Therefore, the side product would be bromomethane.

Other than that, your mechanism is looking good.
I propose:

1. [Hydrolysis of ester to acid through basic hydrolysis](http://www.mhhe.com/physsci/chemistry/carey/student/olc/ch20reactionsesters.html#hydrolysis)
2. [Halogenation of the double bond](http://www.mhhe.com/physsci/chemistry/carey/student/olc/graphics/carey04oc/ref/ch06halogenation.html)
3. [Having in mind the leaving groups](http://www.mhhe.com/physsci/chemistry/carey/student/olc/graphics/carey04oc/ref/ch08leavinggroups.html), you get the desired cycle.