Development of atropisomeric P, N-type ligands and their applications in Suzuki-Miyaura coupling

Abstract

Biaryl structural motif is an important skeleton in natural products from various origins and has a wide range of biological properties. Indeed, SuzukiMiyaura coupling is one of the most widely used approaches for the construction of the biaryl skeleton due to its high compatibility of functional groups and relatively environmentally benign of the side products. Hemilabile P,N-type ligands have recently become a popular topic of organometallic research. Such ligands consist of strongly bonding phosphino groups and weakly coordinating nitrogen moieties for late transition-metal. This thesis describes the development of tunable atropisomeric P,N-type ligand containing benzimidazolyl indole backbone and their applications in SuzukiMiyaura cross-coupling of aryl chlorides and arylboronic acids. This new series of ligands embodies a highly tunable, yet easily accessible main skeleton with a hemilabile coordinating site. Its high efficacy for Suzuki-Miyaura cross-coupling of aryl chlorides in the presence of low Pd-catalyst loading (0.0025%) was found and highly challenging tri-ortho-substituted biaryl synthesis was achieved. Moreover, we have attempted to develop chiral P,N-ligands containing benzimidazolyl indole backbone. The asymmetric SuzukiMiyaura cross-coupling employing these chiral P,N-ligands has been explored. The experimental results showed that (S, Ra)-L6-Ph is an efficient ligand to facilitate asymmetric SuzukiMiyaura cross-coupling with moderate enantioselectivity (ee = 28%) in 73% yield at 70 °C. It is our pursuit to develop efficient chiral catalyst for high value chiral molecule syntheses, especially in the field of asymmetric SuzukiMiyaura coupling. These studies potentially offer a new direction in the design and synthesis of highly active chiral catalysts.