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.