Pd(II)–Prolinate Prolinium and Pd(II)–LysGly Complexes Catalyzed the Enantioselective Aldol, Morita–Baylis–Hillman and Heck Reactions

The induction of chirality to obtain enantiopure products of high synthetic value is of great importance across various scientific fields, particularly in the medical area, as it has been demonstrated that the different enantiomers of drugs interact differently with biological receptors. In this context, asymmetric catalysis focuses on the design of catalysts that are easy to synthesize, capable of efficiently and enantioselectively forming C-C bonds, and suitable for reuse in multiple catalytic processes. This work describes the application of a Pd(II) complex coordinated with the R and S forms of proline in direct Aldol, Morita-Baylis-Hillman, and Heck coupling reactions. The catalytic system efficiently promoted the aldol reaction, achieving yields of 80-95%, excellent diastereoselectivities (1:69 <i>syn</i>/<i>anti</i>), and enantiomeric excesses greater than 99%. From a mechanistic perspective, the formation of a transition state is proposed in which a proline molecule generates an enamine that, upon coordination with the metal center, is stabilized through interaction with the intermediate's double bond. Moreover, the study of the Morita-Baylis-Hillman and Heck coupling reactions highlights the versatility of this type of catalyst.