Experimental and Theoretical Study of Phosphine-Catalyzed Reaction Modes in the Reaction of -Substituted Allenes with Aryl Imines

A new phosphine-catalyzed reaction of alpha-substituted allenes with aryl imines, in stark contrast to classic cycloaddition reactions, has been developed. This reaction delivers valuable highly functionalized itaconimides with excellent stereoselectivities by a new << un-cyclizing >> reaction mode involving beta '-carbon of alpha-substituted allenes. Moreover, the present << un-cyclizing >> reaction can also be carried out in a one-pot fashion and scaled up to the gram scale by using aryl aldehydes, without the need to isolate the aryl imines. Mechanistic studies and control experiments reveal the crucial role of H2CO3 for the present reaction mode. In addition, density functional theory (DFT) calculations were performed to understand the possible mechanism. A phosphine-catalyzed reaction of alpha-substituted allenes with aryl imines delivers valuable highly functionalized itaconimide derivatives with excellent stereoselectivities: The reaction was found to exhibit an unusual << un-cyclizing >> reaction mode involving the beta '-carbon position of alpha-substituted allenes under mild conditions. Mechanistic studies and control experiments reveal the crucial role of H2CO3 for the present reaction mode.+image