Current Progress in Nitrogen Based Chiral Ligands for Pd-catalyzed Asymmetric Transformations

Chiral ligands perform the vital role in enantioselective transition-metal mediated reactions. The accomplishment of N-based chiral ligands is due to the inherent air stability, electron-rich, neutral ligands for homogeneous catalysis. Above all, the easy access and diversity in the core structure as a template for asymmetric reactions led to the experimentation and establishment of diverse chiral N-based backbone as stereodirecting ligands for a variety of asymmetric reactions. The wide efficacy of these ligands is established by the high enantioselectivity persuaded in a variety of transition metal mediated enantioselective reactions, for instance, redox reactions, cycloadditions and carbonheteroatom and carbon-carbon bond making reactions. Due to the modular architecture and the ease of access from the chiral pool, the N-based chiral ligands are readily available. In this review, we will highlight selected examples of N-based chiral ligands which have endowed high enantioselectivity in Pd-mediated asymmetric transformations. The enantioselective aptitude of chiral N-based ligands in Pd-catalyzed reactions is demonstrated largely by the nature of coordinating atoms and the structure of the ligand. Using N-based chiral ligands, excellent yields and enantioselectivities have been obtained. The ligand classification in this review is based upon the ligand framework, hoping to inspire the development of next-generation N-based chiral ligands with innovative enantioselective transformations. Keywords: N-based chiral ligand, asymmetric catalysis, homogeneous catalysis, enantioselective synthesis, ligand development, palladium, cross coupling.