I. scandium (III) catalyzed Nazarov cyclization of heteroaryl-vinyl ketones : II. Efforts towards the total synthesis of (±) - rocaglamide via a Nazarov cyclization strategy ; III. Efforts towards the total synthesis of (±) - rocaglamide via an alkoxy allene epoxidation/Nazarov cyclization
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Thesis (Ph. D.)--University of Rochester. Dept. of Chemistry, 2009.
I. Scandium (III) Catalyzed Nazarov Cyclizations of Heteroaryl-Vinyl Ketones
This chapter describes the successful development of a catalytic method for the Nazarov cyclization of heteroaryl-vinyl ketones. First, a brief survey the history and current state of the field will be outlined. This will illustrate the gap in synthetic utility that existing Nazarov methods cannot address. Then, an outline of the plan by which it will be attempted to address these deficiencies will be presented. Finally, a chronicle of the successful development of a system, that effectively cyclizes a range of heteroaromatic Nazarov substrates under mild conditions, will be presented. This method employs scandium triflate as the Lewis acidic catalyst. During the course of these studies it was determined that the addition of lithium perchlorate to the reaction mixture greatly increased the efficiency of this process. A study of counterion effects led to the proposal that scandium perchlorate is the active catalyst in this system.
II. Efforts Towards the Total Synthesis of (±) - Rocaglamide via a Nazarov Cyclization Strategy
This chapter is concerned with the total synthesis of (±) – rocaglamide, a cyclopenta[b]tetrahydrobenzofuran natural product. First, a brief introduction of the molecule and its related family of natural products will be presented. Then, an outline of previous successful syntheses of this densely functionalized molecule will be discussed. Finally, several approaches to this molecule will be disclosed. Each centers around a key Nazarov cyclization. Unfortunately, none of these approaches resulted in the total synthesis of the target.
III. Efforts Towards the Total Synthesis of (±) - Rocaglamide via an Alkoxy Allene Epoxidation/Nazarov Cyclization
This chapter is concerned with a new approach to the synthesis of (±) – rocaglamide. Reevaluation of the previous unsuccessful attempts led to a better understanding of the electronic bias inherent in the pentadienyl cation of this system. Using this new knowledge, an unprecedented Nazarov cyclization has been developed in which the pentadienyl cation is generated from the ring opening of an alkoxy allene oxide. Elaboration of the product of this reaction facilitated the total synthesis of (±) – aglafolin.
I. scandium (III) catalyzed Nazarov cyclization of heteroaryl-vinyl ketones : II. Efforts towards the total synthesis of (±) - rocaglamide via a Nazarov cyclization strategy ; III. Efforts towards the total synthesis of (±) - rocaglamide via an alkoxy allene epoxidation/Nazarov cyclization
