Phosphine‐Catalyzed Preparation of α‐Imidocinnamates: Stereoselective Synthesis and Mechanism Investigation

Regio‐ and stereoselective addition of cyclic imides and hydantoins to the ethyl phenylpropiolate under mild conditions (in dichloromethane at room temperature), catalyzed by triphenylphosphine, was used to synthesize nine α‐substituted cinnamates, which were characterized by NMR, IR, and ESI‐HRMS data. Solid state structures were obtained by the monocrystal X‐ray analysis. Possible mechanism of the catalytic process was proposed on the base of quantum‐chemical calculations, according to which the stereoselectivity determining factors are proton transfer from α‐ to β‐carbon atom, the preferable conformation of the last intermediate, the difference in energy barrier for E‐ and Z‐products formation and the thermodynamic preference of Z‐product.