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

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.