<i>N</i>‐Nitroso As A Novel Directing Group in Transition‐Metal‐Catalyzed C(<i>sp</i>^<i>2</i>)−H Bond Functionalizations of <i>N</i>‐Nitrosoanilines

In the last few decades, the syntheses of bioactive natural products and functional materials have been achieved via C−H bond functionalizations where the transition metals in coordination with the directing groups trigger the C−H bond activation. A wide variety of directing groups has been recognized for transition‐metal‐catalyzed ortho ‐C−H bond functionalization of arenes. Recently, N ‐nitroso group has been established as a new, efficient and sometimes as a traceless directing group in ortho ‐C(sp 2 )−H bond functionalizations of N ‐nitrosoanilines. During functioning as a traceless‐directing‐group, the N ‐O bond of N ‐nitrosoaniline acts as an internal oxidant to recycle the employed catalyst. Pd, Rh, Co, Ru and Ir catalysts have been screened for the ortho C−H bond functionalizations of N ‐nitrosoanilines constructing new C−C, C−O, C−N and C−X bonds. Herein, we have summarized all the recently developed N ‐nitroso group directed ortho ‐C(sp 2 )−H bond functionalization reactions of N ‐nitrosoanilines.