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.
Borane-mediated hydride abstraction has been shown to
be a powerful
tool for the C(sp3)–H functionalization of amines,
but the same activity with ethers is unknown in the literature. Herein,
we report that this activity was observed with 2H-chromenes and the catalytic C(sp3)–H functionalization
reaction based on this activity was established by using silyl ketene
acetals as the nucleophiles.
We have developed am ethod for the highly diastereo-and enantioselective construction of 2,3-dihydrobenzofurans bearing tetrasubstituted carbon stereocenters by means of annulation reactions between carbenes and 2-iminylor 2-acyl-substituted phenols through catalysis by readily accessible copper(I)/bisoxazoline catalysts under mild conditions.These reactions feature aunique mechanism in whichthe copper catalyst serves ad ual function:f irst it reacts with the diazoc ompound to generate am etal carbene,a nd second, upon formation of an oxonium ylide,itacts as aLewis acid to activate the imine or ketone for diastereo-and enantioselective cyclization.Scheme 1. Syntheses of 2,3-dihydrobenzofurans.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.