Palladium(II)‐Catalyzed One‐Pot Syntheses of 9‐(Pyridin‐2‐yl)‐9H‐carbazoles through a Tandem CH Activation/CX (X=C or N) Formation Process

A new one-pot synthesis of 9-(pyridin-2-yl)-9H-carbazoles through the simultaneous CH activation and palladium(II)-catalyzed cross-coupling of N-phenylpyridin-2-amines with potassium aryltrifluoroborates is presented. Silver acetate and 1,4-dioxane proved to be the best oxidant and solvent, respectively. The product yields fluctuated from modest to excellent and the reaction showed sufficient functional group tolerance. p-Benzoquinone served as an important ligand for the transmetalation and reductive elimination steps in the catalytic process. The kinetic isotope effects (kH/kD) for the first and second CH activation/CC or CN formation steps were measured as 2.14 and 1.18, respectively. Finally, a rational catalytic mechanism is presented based on all experimental evidence.