β-Acylation of Ethyl Pyrrole-2-carboxylate by Friedel-Crafts Acylation : Scope and Limitations (Synthetic Studies on Indoles and Related Compounds. XXXVIII)

The Friedel-Crafts acylation of ethyl pyrrole-2-carboxylate (3) was studied under several conditions using various Lewis acids and acyl chlorides. The acylation with various acyl chlorides in the presence of aluminum chloride gave exclusively ethyl 4-acylpyrrole-2-carboxylate (5), whereas weaker Lewis acids such as zinc chloride and boron trifluoride etherate gave a mixture of ethyl 4- and 5-acylpyrrole-2-carboxylates.