Stereoselective Synthesis of Tetra-Substituted Olefins via Addition of Zinc Enolates to Unactivated Alkynes.

In the presence of a stoichiometric or catalytic amount of diethylzinc, a β-aminocrotonamide undergoes sequential addition/isomerization reactions with 1-alkyne to produce, upon hydrolysis, an α-alkylidene β-dicarbonyl compound in a highly stereoselective manner. The method complements the conventional Knoevenagel synthesis of this class of compounds as to the choice of the starting material and the scope and stereochemistry of the product.