Bronsted Acid-Catalyzed Carbocyclization of 2-Alkynyl Biaryls

Ortho-alkynyl biaryls react in the presence of catalytic amount of Bronsted acids to give phenanthrenes in high yields under mild conditions. The activity and selectivity of this transformation are governed by the substitution pattern of the diarylalkyne moiety. Selectivity shifts are observed between the carbophilic Lewis and Bronsted acidcatalyzed cycloisomerization involving alkyne activation.