A Study of Polarization and Directing Effects of Unsymmetrical Alkynes Using Regioselective Pd‐Catalyzed Bromoallylation

Herein is disclosed the first comprehensive study of factors that affect the regioselectivity of PdBr 2 (PhCN) 2 ‐catalyzed bromoallylation of unsymmetrically substituted internal alkynes. The study was performed on a wide array of electronically and structurally diverse alkynes with aryl‐aryl, aryl‐ferrocenyl, and aryl‐alkyl substitutions. The regioselective formation of bromoallylation products was mostly driven by the polarization of the triple bond in aryl‐aryl and aryl‐ferrocenyl‐substituted ethynes. On the other hand, directing effect, which arises from the presence of a directing group in the side‐chain of aryl‐alkyl‐substituted alkynes, was the dominating factor that determined the regioselectivity of these reactions.