an efficient catalyst for a double Friedel–Crafts reaction of various heteroarenes, i.e. 2-methylfuran, 2-ethylfuran, 2-methylthiophene, pyrrole, N-methylpyrrole and indole, using aldehydes as alkylating agents under “open-flask” conditions with toluene or water as the reaction media. In the presence of 10 mol% iodine in toluene at room temperature, both aliphatic and aromatic aldehydes reacted smoothly