cine Substitution and the Cu Effect in Stille Cross‐Coupling Reactions: Mechanistic Perspectives and Synthetic Utility
cine Substitution arising from slow transmetallation occasionally occurs in classic Pd-catalyzed Stille cross-coupling reactions with sterically hindered vinyltin components. Mechanistic explanations of this "abnormal" cross-coupling mode and the intriguing co-catalytic effects of metallic Cu species in restoring the ipso selectivity are summarized. Typical synthetic applications of this unique Cu effect and the advent of Cu-catalyzed Stille-type cross-coupling are also demonstrated.