Phosphine‐Catalyzed Direct δ‐Carbon Addition of Alkynones to Electron‐Deficient Carbonyl‐Group‐Containing Compounds: Preparation of Conjugated Dienes

The formerly unexplored δ‐carbon of alkynones could be activated as a nucleophilic reaction site and trapped by electron‐deficient carbonyl‐group‐containing compounds upon phosphine catalysis, which provided three kinds of δ‐addition and isomerization products in moderate to excellent yields. Plausible mechanisms were proposed on the basis of deuterium‐labeling experiments. Thus, a novel strategy for phosphine‐catalyzed δ‐carbon addition of alkynones to electron‐deficient carbonyl groups was developed, affording the corresponding substituted 3,5‐dien‐2‐one derivatives under mild conditions.