A Tunable Route to Prepare α,β-Unsaturated Esters and α,β-Unsaturated-γ-Keto Esters through Copper-Catalyzed Coupling of Alkenyl Boronic Acids with Phosphorus Ylides

A tunable strategy to prepare ,-unsaturated esters and ,-unsaturated--keto esters in good to excellent yields was developed through copper-catalyzed oxidative coupling of phosphorus ylides with alkenyl boronic acids under mild conditions. The reaction without water afforded ,-unsaturated esters, ketones, and amides while ,-unsaturated--keto esters, 1,4-,-unsaturated diketones and ,-unsaturated--keto amides were obtained when using 5.0equiv. of water. H2O18 labeling experiments showed that water played an important role in the formation of ,-unsaturated--keto esters. A plausible formation mechanism for ,-unsaturated esters and ,-unsaturated--keto esters was proposed based on mechanistic studies. Phosphonium salts could also be used directly as coupling partners instead of phosphorus ylides. The reaction exhibited a broad substrate scope, good functional group tolerance, good regioselectivity, and diverse coupling products.