Copper‐Catalyzed Asymmetric Annulation Reactions of Carbenes with 2‐Iminyl‐ or 2‐Acyl‐Substituted Phenols: Convenient Access to Enantioenriched 2,3‐Dihydrobenzofurans.

We have developed a method for the highly diastereo‐ and enantioselective construction of 2,3‐dihydrobenzofurans bearing tetrasubstituted carbon stereocenters by means of annulation reactions between carbenes and 2‐iminyl‐ or 2‐acyl‐substituted phenols through catalysis by readily accessible copper(I)/bisoxazoline catalysts under mild conditions. These reactions feature a unique mechanism in which the copper catalyst serves a dual function: first it reacts with the diazo compound to generate a metal carbene, and second, upon formation of an oxonium ylide, it acts as a Lewis acid to activate the imine or ketone for diastereo‐ and enantioselective cyclization. [ABSTRACT FROM AUTHOR]