Ring expansion has taken place which suggests the formation of an intermediate,hence it might be a first order reaction.
Since a doube bond is formed, it might be Elimination reaction.
Hence a probable reaction mechanism is
"It does not do to dwell on dreams and forget to live, remember that." ~Albus Dumbledore, Sorcerer's Stone.
"It is our choices, Harry, that show what we are, far more than our abilities." ~Albus Dumbledore, Chamber of Secrets.
"Understanding is the first step to acceptance, and only with acceptance can there be recovery." ~Albus Dumbledore, Goblet of Fire.
"Do not pity the dead Harry, pity the living, and above all, those who live without love." ~Albus Dumbledore, Half Blood Prince.