A Novel Palladium-Catalyzed Synthesis of Phenanthrenes from ortho-Substituted Aryl Iodides and Diphenyl- or Alkylphenylacetylenes

1,5-Selectively disubstituted 9,10-diphenyl- or alkylphenylphenanthrenes are obtained by reaction of ortho-substituted aryl iodides and diphenyl- or alkylphenylacetylenes in the presence of palladium and norbornene as catalysts. The reaction outcome is controlled by the steric effect exerted by the ortho substituent in the aryl iodide.