What would be the mechanism of the given reaction? Problem:


  
  
  $\ce{A}$ can be?
  
  
  concentrated sulphuric acid
  alcoholic potassium hydroxide
  triethylamine
  potassium tert-butoxide
  


My comments:

Option (A): Conc. $\ce{H2SO4}$, is an acid, it gives $\ce{H+}$ ions which must act like electrophile and add to the double bond, which must produce a carbocation and then, $\ce{HSO4^-}$ ion must act like a nucleophile and form a bond with the carbocation. Hence, the reaction must be addition of $\ce{H+}$ and $\ce{HSO4^-}$

Options (B),(C),(D): are bases, with basicity order: (D) > (B) > (C). But what would they do to an alkene?

Answer given in the book is A. How is this so?
Bottom line: $\ce{HSO4-}$ is a really bad nucleophile, and it doesn't enter in the picture. 



(I realize after scanning that I'm missing the "+ H+" alongside the final product.)



Question for extra credit: after the second step, why is the third step (carbocation migration) favorable rather than directly reforming the double bond on the right-hand side ring?