As shown above, the original plan is to synthesize compound 2 from compound 1. Before the reaction, the major concern is the forming compound 3 which maybe is hard to separate from 2. However, when 1 was treated with TfOH at 60 degree for three hour, compound 4 was generated as the major product with a yield of around 70%. The desired product 2 is just a minor product with a yield of 20%.

Compound 2 can be isolated from 4 since 2 is very soluble in CHCl3 but 4 is not soluble in CHCl3 at all.

The lesson learned form this example is that trifluoromethyl group is not stable at strong acidic condition. Another lesson learned from this case is PPE is always important since anything can happen during a new reaction. In this reaction, mostly lots of HF had been produced.