Asymmetric carbon–carbon bond formation reactions are some of the most important processes, which enable key steps in building of complex molecules. The palladium-catalyzed asymmetric carbon–carbon bond formation is one of the most popular methods for accessing chiral molecules. Ligand design and synthesis are very important for facilitating palladium-catalyzed reactions. Among numerous ligands, hemilabile ligands attract much attention due to their unique structural properties. In our group’s prior studies, aromatic amide-derived phosphines (Aphos) and atropisomeric 1-naphthamide-derived phosphines (A²phos) have demonstrated as the achiral and chiral hemilabile P,O-ligands, respectively. Aphos shows its efficiency in palladium-catalyzed room-temperature Suzuki–Miyaura reaction of unact...[ Read more ]

Asymmetric carbon–carbon bond formation reactions are some of the most important processes, which enable key steps in building of complex molecules. The palladium-catalyzed asymmetric carbon–carbon bond formation is one of the most popular methods for accessing chiral molecules. Ligand design and synthesis are very important for facilitating palladium-catalyzed reactions. Among numerous ligands, hemilabile ligands attract much attention due to their unique structural properties. In our group’s prior studies, aromatic amide-derived phosphines (Aphos) and atropisomeric 1-naphthamide-derived phosphines (A²phos) have demonstrated as the achiral and chiral hemilabile P,O-ligands, respectively. Aphos shows its efficiency in palladium-catalyzed room-temperature Suzuki–Miyaura reaction of unactivated aryl chlorides, while A²phos has been applied to palladium-catalyzed asymmetric allylic alkylation (AAA), asymmetric Heck reaction (AHR), and asymmetric Suzuki–Miyaura cross-coupling. A brief introduction on hemilabile ligands, especially P,O-ligands, and their applications in catalytic carbon–carbon bond forming reactions is given in Chapter 1.

This thesis research focuses on synthesis of novel A²phos by modifying the nitrogen substituents and C4 appendage of the 1-naphthamide scaffold. Three methods are used for preparation of enantiopure A²phos, including HPLC resolution over a chiral stationary phase, chemical resolution, and derivation via the self-assisted molecular editing (SAME) approach. The details of A²phos synthesis and characterization are found in Chapter 2.

Palladium-catalyzed AHR has been studied using the newly synthesized A²phos as described in Chapter 3. We have examined AHR of the methoxy-substituted 1-naphthyl triflates with 2,3-dihydrofruan. It has been found that A²phos possessing 2-diphenylphosphino moiety does not promote formation of the isomerized Heck product while enantioselectivity of AHR correlates with bulkiness of the amide subunit. The AHR products are obtained in excellent yields and with 54–69% ee.

Asymmetric Suzuki–Miyaura cross-coupling appears to be the most promising tool for synthesis of chiral biaryls. In Chapter 4, we have investigated asymmetric Suzuki–Miyaura cross-coupling of aryl halides and aryl boronic acids by using the novel C4-substitued A²phos. Enhanced reactivity for the coupling partners appended with bulky ortho-substituents has been observed, resulting in improved yields and enantioselectivity of the chiral biaryl products in some cases. Another original contribution of the current study is the determination of absolute configuration of some chiral biaryls by combination of X-ray crystal structural analysis and chemical transformations. Our study also suggests that atroposelective reductive elimination may be the stereochemical determination step of asymmetric Suzuki–Miyaura cross-coupling reaction.

Overall, this thesis presents a compilation of our original results in the area of A²phos ligands synthesis and application in asymmetric Heck and Suzuki–Miyaura cross-coupling reactions. The current work expands the scope of A²phos structural diversity and defines the catalytic limitations in the two important carbon–carbon bond forming reactions.