Phosphane‐Catalyzed Umpolung Addition Reaction of Nucleophiles to Ethyl 2‐Methyl‐2,3‐butadienoate

Abstract The phosphane‐catalyzed umpolung addition of various nucleophiles to ethyl 2‐methyl‐2,3‐butadienoate is described. Oxygen, nitrogen, and carbon nucleophiles smoothly reacted with ethyl 2‐methyl‐2,3‐butadienoate to give the corresponding umpolung addition products in good to excellent yields by a similar reaction mechanism. For sulfur nucleophiles, the addition reactions with ethyl 2‐methyl‐2,3‐butadienoate proceeded by a different mechanism.