Palladium on carbon-catalyzed synthesis of 2- and 2,3-substituted indoles under heterogeneous conditions.

A mild, efficient and LiCl-free synthetic method for indole derivatives based on the heteroannulation of alkynes with 2-iodoanilines was achieved using palladium on carbon (Pd/C) and NaOAc in heated NMP. The N-tosyl protection of 2-iodoaniline expedited the reaction progress, while other protecting groups, such as tert-butoxycarbonyl, acetyl, and benzyloxycarbonyl groups, underwent deprotection under the present conditions. A variety of di- and monosubstituted alkynes could effectively react with N-tosyl-2-iodoaniline to give the corresponding indoles in good to high yields.