AgBF ₄ ‐Induced Site‐Selective Synthesis of 4‐Sulfonylindoles in Au‐Catalyzed Cyclization‐Sulfonyl Migration Reactions

ABSTRACT The reactions of ortho ‐alkynyl‐ N ‐arenesulfonylanilines in the presence of SPhosAuCl (2 mol %) and AgBF 4 (6 mol %) produced the corresponding 4‐sulfonylindoles in good yields with satisfactory site‐selectivity at the C4‐position of the indole ring. This reaction proceeded via cyclization followed by sequential [1,2]‐rearrangement of the sulfonyl group. The selective migration of the sulfonyl group to the C4‐position was induced by using an excess amount of AgBF 4 relative to the gold catalyst to form a dinuclear Au─Ag complex to decelerate the migration to C3‐position. Furthermore, the tetrafluoroborate anion with its suitable gold affinity and hydrogen bonding characteristics, plays a crucial role in enabling selective migration to the C4‐position.