B(C ₆ F ₅ ) ₃ ‐Catalyzed Synthesis of Symmetrical and Unsymmetrical 3,3ʹ‐Bisindoles with an All‐Carbon Quaternary Center from α‐Keto Thioesters and Oxoesters

Abstract α‐Keto thioesters can undergo B(C 6 F 5 ) 3 ‐catalyzed symmetrical and unsymmetrical bisindolylation in a chemoselective manner when reacted with substituted indoles under mild conditions in 1,2‐dichloroethane solvent. This reaction demonstrates compatibility with a broad range of α‐keto thioesters that feature aliphatic and aromatic substituents, yielding 3,3ʹ‐bisindoles with an all‐carbon quaternary center at good‐to‐excellent yields (up to 98%). Notably, the weak C(O)−S bond in α‐keto thioesters remains intact despite the presence of a nitrogen nucleophile. A similar transformation has also been successfully achieved with analogous oxoesters, showing excellent efficiency. Furthermore, we have demonstrated that unsymmetrical 3,3ʹ‐bisindoles can be synthesized from a symmetrical one using the same reaction conditions. This approach has also been extended to the synthesis of 3,3ʹ‐bis(indolyl)hydrazides through the cleavage of the C(O)−S bond in bisindole derivatives.