Palladium‐Catalyzed Trimerizations of Terminal Arylalkynes: Synthesis of 1,3‐Diaryl‐2‐arylethynyl‐1,3‐butadienes [1]

Various 1,3‐diaryl‐2‐arylethynyl‐1,3‐butadienes 7 have been prepared by the Pd‐catalyzed trimerization of arylalkynes 4 . Their structures and stereochemistry have been confirmed by X‐ray crystal analyses. This procedure provides high regioselectivity to generate adducts Z ‐ 7 in moderate to excellent yields. The scope, limitations and regioselectivity of this reaction have been investigated. In DMSO at 180 °C, 1,3‐di(1‐naphthalenyl)‐2‐(1‐naphthalenylethynyl)‐1,3‐butadiene ( 7m ) underwent 6π‐electrocyclization to form 2‐(1‐naphthalenyl)‐3‐(1‐naphthalenylethynyl)‐1,2‐dihydrophenanthrene ( 21 ). Under acidic conditions, (1 Z ) ‐ 1,3‐diphenyl‐2‐(1‐phenylethynyl)‐1,3‐butadiene ( Z ‐ 7a ) was converted to 1‐methyl‐3‐phenyl‐2‐(2‐phenyl‐1‐ethionyl)‐2‐indene ( 22 ) in 75% yield.