The Syntheses of Hyacinthacine A1 and Planar [10]Annulenes

Abstract

Aromaticity is a fundamental concept that has effectively permeated all facets of chemistry. Though our understanding of the subject is not complete, our working understanding has led to many developments in pharmaceuticals and materials research. There are currently several avenues of research that can progress the field even further. First, exploring the chemical reactivity of aromatic systems (chapter 2) under novel conditions serves to expand our toolkit as organic chemists. The preparation of novel aromatic systems (chapters 3-4) also seeks to advance our understanding of the limits of the phenomenon. Finally, the quantification of aromaticity (chapter 5) is generally only possible by computational methods and since aromaticity manifests in several ways, there are many descriptors that are possible to explore. It was hypothesized that carrying out an NHC catalyzed cross-benzoin reaction and subsequent furan photooxygenation-amine cyclization (hereafter simply referred to as “photooxygenation”) of the resulting transformed products can generate a substrate that is amenable to transformation into the hyacinthacine A1 core (chapter 2). This type of a photooxygenation has never been accomplished with polyhydroxylated frameworks. The successful implementation of the transformation demonstrates its viability and opens the possibility for the synthesis of various hyacinthacine diastereomers. The preparation of planar [10]annulenes has been a long standing goal for synthetic and physical organic chemists. The successful preparation of a bench stable [10]annulene would allow chemists to probe the effects of ring size on aromaticity experimentally. In chapters 3-4, a little used endo-to-exo cyclopropene isomerization is exploited to generate a series of cyclopropanated [10]annulene frameworks. Though it is a well-known concept, aromaticity is quite a difficult concept to grasp, and even more challenging to quantify. Many of the current quantification methods are often highly esoteric and inaccessible to experimentalists. Chapter 5 investigates the use of natural bond orbitals (NBOs) for the quantification of aromaticity. NBOs provide a highly intuitive (2c-2e-|) picture of structure and bonding and have aided in the understanding of stereoelectronic effects. Extending their use to the study of aromaticity permits chemists to use their ingrained intuition to understand aromaticity as a series of pi−>pi* interactions. These chapters all combine to progress the field of aromaticity further in their own ways and ultimately describe successful pursuits. The demonstration of novel reactivity of furans within a total synthesis, the preparation of long sought-after aromatic frameworks, as well as a new lens for aromaticity have all been accomplished.