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

A new one-pot synthesis of 9-(pyridin-2-yl)-9H-carbazoles through the simultaneous C?H 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 C?H activation/C?C or C?N formation steps were measured as 2.14 and 1.18, respectively. Finally, a rational catalytic mechanism is presented based on all experimental evidence.