Novel and Efficient CeCl3.7H2O/NaI-Catalyzed Sulfenylation of Indoles and Pyrroles

The preparation and manipulation of functionalized low molecular weight heteroaromatic compounds is of increasing importance for obtaining new more potent pharmaceuticals [1]. In particular, 3-sulfenyl indoles (4) and 2-sulfenyl pyrrole (5) are an important class of compounds due their activity towards the treatment of several deseases [2], and as inhibitors in medicinal chemistry [3]. Most of methods for their preparation are based on electrophilic aromatic sulfenylation, but a considerable number of them have been unsatisfactory because the procedures provide low yields of the desired products, and/or require harsh conditions that are incompatible with sensitive functional groups [4]. In the framework of our ongoing program in the development of Lewis acid-catalyzed reactions by CeCl [5], we have developed a new general and efficient methodology for the sulfenylation of indoles 1 and pyrroles 2 by N-(alkylthio)- and N-(arylthio)phthalimides (3) in the presence of our combination CeCl3.7H2O/NaI.