Regioselectivity Switch Based on the Stoichiometry: Stereoselective Synthesis of Trisubstituted Vinyl Epoxides by Cu‐Catalyzed 3‐ <i>exo</i> ‐ <i>trig</i> Cyclization of α‐Allenols

Typical transition metal-catalyzed oxycyclization of allenols takes place at the terminal allene carbon via a 5-endo path and forms dihydrofurans. A copper-catalyzed protocol brought about reversed regioselectivity, generating series trisubstituted epoxides through 3-exo-cyclization/sulfonylation cascade. The current stoichiometry control regioselectivity may open singular opportunities in chemical transformations.