Total Synthesis of the Tubingensin Alkaloids
This dissertation describes the total syntheses of the indole diterpenoid natural products, tubingensin A & B. Central to the syntheses of these molecules was the use of heterocyclic aryne intermediates, which are highly reactive and can facilitate difficult bond formations. We describe the formation of vicinal quaternary centers using this methodology in what are some of the most stereochemically complex examples of aryne reactions.
Chapter One reviews the impact that indole diterpenoid natural products have had on chemical synthesis. This class of compounds has provided inspiration for the development of useful chemical methods and strategies. Natural products discussed include penitrem D, paspaline, emindole SB, dixiamycin B, and tubingensins A & B.
Chapter Two describes the total syntheses of (+)-tubingensin A. Vital to the success of the route was the use of heterocyclic aryne chemistry as well as a B-alkyl Suzuki–Miyaura reaction. The synthesis proceeded in only nine steps, longest linear sequence.
Chapter Three pertains to the synthesis of the more complex natural product, (–)- tubingensin B. The synthesis relied on a similar B-alkyl Suzuki–Miyaura reaction, a carbazolyne cyclization, and a radical cyclization to construct the core architecture of the molecule. The synthesis represented one of the biggest structural challenges addressed by heterocyclic aryne chemistry.