Regioselective [3 + 2] Annulation of β,γ-Alkynyl-α-ketimino Esters with 1,3-Dicarbonyls: The Synthesis of Highly Functionalized Dihydrofurans

A regioselective [3 + 2] annulation of β,γ-alkynyl-α-ketimino esters with 1,3-dicarbonyls is disclosed. A series of Z-selective dihydrofurans bearing an exocyclic double bond and a quaternary carbon center are accessed without the usage of base. Control and deuterium-labeling experiments have been investigated to probe into the reaction mechanism. The catalyst and base-free nucleophilic addition highlights the transformation.