# Is Pinacol rearrangement the source for the ring expansion?

I have no idea what's happening as in the product (the answer is (a)) there is a new ring being formed on the left benzene. But as I studied after $$\ce{H2O}$$ leaves, a carbocation is then formed on stabilized by the right ring.

Can someone please explain the rest of the steps of this reaction? The thing I don't get is how does the three-membered ring opening happens. I attempted the question, but the answer that I came up with isn't the one matching in the book. Where did I go wrong with the mechanism?

• Here is a hint. Form the most stable cation, migrate a C-C bond and do a Nazarov cyclization (Google it). To the rest of the audience, allow aditya to work on a solution before posting an answer. Dec 10, 2019 at 21:53
• Thanks I tried to attempt the question as per your suggestion but I didn't came to the right conclusion can you have a look on the mechanism as I have added it in the question. Dec 11, 2019 at 3:49