Rhodium-Catalyzed Directed C(sp2)–H Bond Addition of 2‑Arylindazoles to N‑Sulfonylformaldimines and Activated Aldehydes

Rhodium-catalyzed directed C–H functionalization of 2-arylindazoles with N-sulfonyl­formaldimines has been developed to provide a variety of N-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.