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Keywords:

  • allylic compounds;
  • C[BOND]H activation;
  • cyclization;
  • palladium;
  • phosphane ligands

Abstract

Pd-catalyzed 5-exo-trig or 6-endo-trig C[BOND]H 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 PdII catalytic center. This character is ultimately defined by the nature of the X ligand in the PdX2 salt serving as an in situ precursor of the active catalytic species involving BIPHIMIP {2-(diphenylphosphino)-1-[2-(diphenylphosphino)phenyl]-1H-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.