Regiospecific C-Acylation of Pyrroles and Indoles Using N-Acylbenzotriazoles

Reactions of pyrrole (2) or 1-methylpyrrole (4) with readily available N-acylbenzotriazoles 1a−g (RCOBt, where R = 4-tolyl, 4-nitrophenyl, 4-diethylaminophenyl, 2-furyl, 2-pyridyl, 2-indolyl, or 2-pyrrolyl) in the presence of TiCl4 produced 2-acylpyrroles 3a−g and 5a−g in good to excellent yields. 1-Triisopropylsilylpyrrole (6) under the same conditions gave the respective 3-acylpyrroles 7a−g. Similarly, indole (9) and 1-methylindole (11) gave the corresponding 3-acylated derivatives 10a−g and 12a−g. These results demonstrate that N-acylbenzotriazoles such as 1c,f,g are mild, regioselective, and regiospecific C-acylating agents of particular utility when the corresponding acid chlorides are not readily available.