Synthesis of 2-Sulfonated-9H-Pyrrolo[1,2-a]indoles via a Ag-Promoted Cascade Sulfonation and Cyclization

An efficient Ag-promoted reaction of N-propargyl indoles and arylsulfinic acids to 2-sulfonated-9H-pyrrolo[1,2-a]indoles was developed. Using arylsulfinic acids as stable and less toxic sulfonylation agent, the reaction proceeded smoothly to give the desired products in good yields and excellent regioselectivity with a broad substrate scope.