Versatile Pd‐Catalyzed CH Oxidative Cyclization of Homoallylhydrazones to Pyrazolines and Tetrahydropyridazines

Pd‐catalyzed 5‐ exo ‐ trig or 6‐ endo ‐ trig CH oxidative cyclization of C ‐homoallyl‐ N ‐sulfonylhydrazones to 5‐vinylpyrazolines or 6‐methylidene‐1,4,5,6‐tetrahydropyridazines, respectively, is shown to be controlled in a highly selective manner by the ionic character of the Pd II catalytic center. This character is ultimately defined by the nature of the X ligand in the PdX 2 salt serving as an in situ precursor of the active catalytic species involving BIPHIMIP {2‐(diphenylphosphino)‐1‐[2‐(diphenylphosphino)phenyl]‐1 H ‐imidazole} as an optimal spectator diphosphine ligand for both processes. Whereas acetates (X=OAc) favor the 6‐ endo process, noncoordinating anions such as tosylates and triflates (X=OTs, OTf) favor the 5‐ exo process.