Celecoxib generated more than $3 billion in worldwide sales in 2016. It is a COX-2 selective nonsteroidal anti-inflammatory drug used to treat a number of different medical conditions. A highly efficient synthesis of celecoxib involves the key step that generates the pyrazole ring.

i) By consideration of the reactivities of the carbonyl groups of the dione and the amino groups of the hydrazine, explain why regioisomer 7 is the main reaction product. (3 marks) 

ii) Provide a mechanism for the above reaction to give 7; the aryl groups may be abbreviated as Ar and Ar’. (5 marks)

F3 CF3 `NH2 N-N H3C cat. HCI H2N-N H3C H ethanol (solvent) heat H2N-S 7