Rhodium-Catalyzed Directed C(sp)-H Bond Addition of 2-Arylindazoles to -Sulfonylformaldimines and Activated Aldehydes.

Rhodium-catalyzed directed C-H functionalization of 2-arylindazoles with -sulfonylformaldimines has been developed to provide a variety of -benzylarylsulfonamide derivatives with good to excellent yields. Different activated aldehydes like ethyl glyoxalate and 2,2,2-trifluoroacetaldehyde also efficiently underwent nucleophilic addition with 2-arylindazoles. These selective transformations occur through the control of C3 nucleophilicity of indazole moiety. Mechanistic studies suggest that C-H activation step may be a rate-limiting step.