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

The formerly unexplored delta-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 delta-addition and isomerization products in moderate to excellent yields. Plausible mechanisms were proposed on the basis of deuteri-um-labeling experiments. Thus, a novel strategy for phosphine-catalyzed delta-carbon addition of alkynones to electron-deficient carbonyl groups was developed, affording the corresponding substituted 3,5-dien-2-one derivatives under mild conditions.