Sulfenate Anion Catalysis: Reactions and Precatalysts Development

Organocatalysts have been a hot area of exploration, due to both concept novelty and significant reactivity. Multiple mechanisms have been proved and used to design new organocatalysts. Examples include thioureas, which have been designed to accelerate chemical transformation through hydrogen bonds. Initially found by Schering and Hoffman-La, prolines have been widely used in asymmetric aldol reactions. This dissertation investigated an unprecedented organocatalyst: sulfenate anions. In Chapter 1, sulfenate anions are introduced as a new type of organocatalyst. It has been well established that the sulfenate anions act both as nucleophiles and leaving groups. For prove-of-concept, a variety of benzyl halides were successfully coupled to form stilbenes. More challenging sulfenate anions precatalysts, including DMSO performed well in these catalytic reactions. Preliminary mechanistic studies were conducted, identifying α-deprotenated sulfoxide as the resting state. In Chapter 2, we further investigated the sulfenate anions capability as organocatalysts. Due to the instability of sulfenate anions in air, sulfoxides precursors are usually used and generate sulfenate anions in situ through base induced beta-hydrogen elimination or thermolysis. tert-Butyl sulfoxides were examined as a new type of organocatalysts precursor with iso-butylene as a byproduct. It is noteworthy that sulfenate anions generated from tert-butyl sulfoxides remain stable in high temperature under inert atmosphere and retain similar reactivity compared with sulfenate anions formed using general conditions in the model reaction of benzyl halides coupling. In Chapter 3, further research was performed in exploring the reaction possibility of sulfenate anions. A cross-coupling reaction of benzyl halides and benzaldehydes derivatives was achieved to form alkyne compounds. A broad scope of alkyne products, including multiple functional groups and heterocycles, demonstrated the value of sulfenate anion catalysts in synthetic chemistry. The reactivity of different functionalized sulfenate anions and sulfoxide precatalysts were examined. Further optimization was conducted to overcome multiple side reactions. Moreover, preliminary mechanism study revealed the role of sulfenate anions in the reaction. In Chapter 4, convenient scalable sulfenate anions precatalysts were developed and their utility demonstrated in a scalable alkyne synthesis