A persistent challenge in the field of natural product total synthesis is the ability to rapidly establish complex carbon frameworks in mild and selective manner. Over the past decades, the development of Au(I)-catalyzed alkyne cyclization reactions enabled organic chemists to forge such complex ring systems in the pursuit of the total synthesis of terpene and alkaloid natural products. In this dissertation, I will review several such reactions, their application to total synthesis, and the synthetic efforts toward the total synthesis of the indole alkaloid koumine, as well as the harziane diterpenoid natural product family.In Chapter 1, I review the reactivity of Au(I) species and provide an overview of the application of Au(I)-catalyzed cyclization reactions. Three distinct reaction types will be discussed: (1) Au(I)-catalyzed Conia-ene reactions between an activated carbonyl and a pendant alkyne, (2) Cyclization reactions of indoles onto alkynes activated by a Au(I) catalyst, and (3) Au(I)-catalyzed cycloisomerization reactions of 1,n-enynes to form several rings in one synthetic step. Chapter 2 will focus on two synthetic efforts toward the total synthesis of koumine. Following a review of the biosynthetic pathway in the producing organism, Gelsemium elegans Benth., we will review previous total and formal syntheses of koumine and discuss the synthetic strategies taken therein. We first attempted to access the framework of koumine via an inverse electron-demand pyridone Diels–Alder reaction and then pivoted to a Au(I)/Ag(I)-mediated cyclization to obtain an intermediate spiroindolenine. Though we were unable to complete the total synthesis of koumine, we have gained insight into the reactivity of the complex frameworks of our synthetic intermediates. Lastly, in Chapter 3, I will focus on our successful total synthesis of harziandione. First, we will review the biosynthesis of the harziane diterpene natural product family and prior synthetic approaches. Then, we will discuss the development of our synthetic strategy, involving a key Au(I)-catalyzed cycloisomerization and a ring contraction event. We will discuss the progression of synthetic approaches taken, discuss undesired results, and summarize the ultimately successful route.