A convenient “one-pot” Friedel–Crafts reaction of mono-, bi- and tert-thiophenes with trifluoroacetic acid anhydride (TFAA) as an acylating agent and magnesium perchlorate dihydrate (anhydron) as catalyst affords trifluoroacetyl-substituted products in high yields. This method provides a novel approach for the synthesis of thiophene based derivatives bearing trifluoroacetyl group. The mechanism of this