Regiospecific C-acylation of pyrroles and indoles using N-acylbenzotriazoles

Reactions of pyrrole (2) or 1-methylpyrrole (4) with readily available N-acylbenzotriazoles la-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.