Palladium-Catalysed Direct Desulfitative Arylation of Pyrroles using Benzenesulfonyl Chlorides as Alternative Coupling Partners

The reactivity of pyrrole derivatives for palladium-catalysed desulfitative arylation has been investigated. 1-Methyl-, 1-phenyl- and 1-benzylpyrroles were successfully coupled with a variety of benzenesulfonyl chlorides using a phosphine-free catalyst. Highly regioselective arylations at carbon C2 of pyrroles were observed in all cases. A wide variety of substituents on the benzenesulfonyl derivative was tolerated. It should be noted that even bromo-and iodo-benzenesulfonyl chlorides were successfully coupled with pyrrole derivatives without cleavage of the C-Br or C-I bonds, allowing further transformations. Surprisingly, with indoles, mixtures of C2- and C3-arylation products were obtained.