INSTALLING Csp3-RICH MOTIFS VIA VISIBLE LIGHT-MEDIATED TRANSFORMATIONS

Studies have found that the three-dimensionality of a drug candidate has a positive correlation with success in clinical trials, which revitalizes general interest in installing Csp3-containing fragments. To satisfy the ever-increasing demand for complexity in drug discovery, visible-light mediated transformations have stood out to become a powerful tool for the installation of Csp3-containing fragments, or alkyl groups, with intricate functional groups via radical pathways. Furthermore, the merger of these processes with metal catalysis has significantly broadened the chemical space of cross-couplings, enabling novel bond formation events. Nonetheless, engaging aliphatic amines, especially unprotected ones, in photoredox catalysis to construct Csp2-Csp3 bonds remains challenging due to the undesired over-oxidation, C-N coupling, and many other side reactions. Chapter 2 describes a solution using the easily accessible α-silylmethylamine to generate α-amino radicals regioselectively under mild reaction conditions and engage them in a rate-matched Ni/photoredox dual catalytic process to generate benzylamines. Subsequent efforts toward installing alkyl substrcutures was focused on the synthesis of bicyclo[1.1.1]pentane (BCP), which is a bioisostere of phenyl-, alkyl- and alkynyl groups. Although in many cases, BCP has brought promising improvement to drug candidates, limitations in synthetic methods to access this unusual motif have become a main hurdle for their application. Chapter 3 describes a transition metal-free approach to 1,3-disubstituted BCP boronates, a class of highly versatile BCP building blocks, from [1.1.1]propellane using carboxylic acid and organohalide feedstock materials. Chapter 4 describes the discovery of a highly selective Ni-catalyzed cyanation process that enables the synthesis of alkyl-, sulfonyl- and carbamoyl-substituted BCP nitriles, another useful BCP building block, in a single-step from [1.1.1]propellane.