[cseil]

I have to propose a mechanism for the following reaction



I started writing the mechanism of the E1.
The product is:



But I don't know how to increase the number of carbons in the cycle.
Could you help me please?
Thank you

[critzz]

Okay, what is the very first step of an E-1-elimination? (also why is it not an E-2-elimination?)

[cseil]

E1 is favoured by a weak base and a protic solvent.
It is the case.

The first step is the formation of the carbocation. The C-Cl bond is broken. The second step is the elimination of the proton.
In this case, the β-carbon is the tertiary carbon of the cycle.

[critzz]

Yes, you are right. Normally the tertiary carbocation would be the most stable one.
However, it has a strained cyclobutyl group next to it that could relieve some strain by rearranging.
Could you draw the initial product?

[cseil]

Yes, you are right. Normally the tertiary carbocation would be the most stable one.
However, it has a strained cyclobutyl group next to it that could relieve some strain by rearranging.
Could you draw the initial product?

Maybe I figured it out.
Is it correct?
Thank you!

[Altered State]

Seems good to me. First rearrangement is favored by the decrease on ring strain and the second one because a more stable carbocation is formed.

[critzz]

Maybe I figured it out.
Is it correct?
Thank you!

Yes, this is what I had in mind.
You're welcome!