Iridium-Catalyzed Asymmetric Ring-Opening of Oxabicyclic Alkenes with Carboxylic Acids

Abstract

A novel iridium-catalyzed asymmetric ring-opening of oxabicyclic alkenes with a variety of carboxylic acids was reported, which afforded the corresponding trans-carboxylic acids 1-hydroxy-1,2-dihydro-naphthalen-2-yl ester products in good yields with moderate enantioselectivities under mild conditions. The trans products are formed via the enantioselective cleavage of a bridgehead carbon–oxygen bond in 1 followed by SN2′ nucleophilic attack by carboxylic acids. The effects of various bisphosphine ligands, Ag(I) salts, ammonium halides, bases, and solvents on the yields and enantioselectivities of the reaction were also investigated. The theoretical analysis of stability and hydrogen bond for 1-hydroxy-1,2-dihydronaphthalen-2-yl 4-chlorobenzoate 2a were performed using the density functional theory B3LYP methods. The trans-configuration of the product 2a was confirmed by X-ray diffraction analysis. A possible mechanism for the present catalytic reaction was proposed. A novel iridium-catalyzed asymmetric ring-opening of oxabicyclic alkenes with a variety of carboxylic acids was reported, which afforded the corresponding trans-carboxylic acids 1-hydroxy-1,2-dihydro-naphthalen-2-yl ester products in good yields with moderate enantioselectivities under mild conditions. The trans products are formed via the enantioselective cleavage of a bridgehead carbon–oxygen bond in 1 followed by SN2′ nucleophilic attack by carboxylic acids. The effects of various bisphosphine ligands, Ag(I) salts, ammonium halides, bases, and solvents on the yields and enantioselectivities of the reaction were also investigated. The theoretical analysis of stability and hydrogen bond for 1-hydroxy-1,2-dihydronaphthalen-2-yl 4-chlorobenzoate 2a were performed using the density functional theory B3LYP methods. The trans-configuration of the product 2a was confirmed by X-ray diffraction analysis. A possible mechanism for the present catalytic reaction was proposed.