Stereoselective Alkyne–Alkene [2 + 2] Cycloaddition Enabled by Anion Relay Chemistry for Fully C-Substituted Cyclobutene Synthesis

Cyclobutenes serve as valuable scaffolds in pharmaceutical development, but synthesizing structurally diverse fully C-substituted cyclobutenes remains challenging. Here we report a stereoselective [2 + 2] cycloaddition between alkynyl 1,3-dithianes and cinnamate esters using a catalytic amount of KO<i>t</i>Bu. Our approach enables the construction of synthetically challenging tetrasubstituted cyclobutenes via anion relay chemistry (ARC), exhibiting excellent <i>trans</i>-diastereoselectivities (dr > 20:1).