Efficient sulfonation of 1-phenylsulfonyl-1H-pyrroles and 1-phenylsulfonyl-1H-indoles using chlorosulfonic acid in acetonitrile

The sulfonation of various 1-phenylsulfonyl-1H-pyrroles and 1-phenylsulfonyl-1H-indoles using chlorosulfonic acid in acetonitrile has been studied, leading to the development of a clean and operationally simple protocol allowing direct synthesis of the corresponding 1-phenylsulfonyl-1H-pyrrole-3-sulfonyl chlorides and 1-phenylsulfonyl-1H-indole-3-sulfonyl chlorides, respectively, both of which may be easily converted to various sulfonamide derivatives by treatment with nitrogen nucleophiles. Efficient and selective removal of the phenylsulfonyl- or tosyl groups in the sulfonamide series may be achieved under mild conditions.