Synthesis and Network Analysis of Substituted Bullvalenes and the Total Synthesis of Endiandric Acid J and Beilcyclone A

Abstract

This thesis is divided into two topics, 1) the synthesis and analysis of bullvalene and substituted bullvalene, 2) and the synthesis of endiandric acid J and beilcyclone A. Bullvalene is the epitome of fluxional molecules. This C10H10 hydrocarbon undergoes an infinite succession of fast sigmatropic Cope rearrangements and exists as an ensemble of 1, 209, 600 degenerate isomers. Substituents on this core structure will explore all possible non– degenerate isomers. Mono substituted bullvalene for instance exists between 4 isomers and disubstituted bullvalene with unidentical substituents interconverts between 30 isomers. With more substituents, the complexity of the molecular system rapidly escalates. Chapter 1 presents a comprehensive history of the synthetic chemistry of bullvalene, written in a review format. In chapter 2 we demonstrate a new method to access bullvalene, as well as mono– and disubstituted bullvalenes in two–steps. A cobalt catalysed [6+2] cycloaddition reaction between cyclooctatetraene and substituted alkynes followed by a photorearrangement gives the desired products. The isomer distribution of these substituted bullvalenes were elucidated using low temperature NMR spectroscopy. Our collaborator Lukáš F. Pašteka developed a computational toolbox to predict the isomer distribution of substituted bullvalenes and reaction graphs display their interconversion network. Despite the efficiency of this method, intrinsic limitations in alkyne substitution patterns prevent access to trisubstituted bullvalenes. Chapter 3 continues the narrative of chapter 2, where we overcome the limitation of our method by introducing a trimethylsilyl group to cyclooctatetraene to access trisubstituted bullvalenes. Surprisingly, all trisubstituted bullvalenes share a kinetically metastable major isomer which is in slow exchange with the rest of the network. Using DFT calculations as well as kinetic simulations we gain a deeper insight on the interconversion network of substituted bullvalenes. In chapter 4 we expand the dynamic behaviour of bullvalene by introducing one or two elements of stereogenicity into the substituents of disubstituted bullvalenes. This leads to the creation of a chemical library which is defined by structure. In this chemical library some isomers show mutating helicity on their bullvalene core by a fast Cope rearrangement, while the stereocentre of their substituent is fixed. The coupling of two disubstituted bullvalenes by a stereogenic tether leads to a structure with three mutating stereogenic elements, where the tethers’ configuration is mutated by the dynamic ensemble of exchanging isomers of the bullvalenes attached to it. Chapter 5 is an introduction to the endiandric acid natural product. Here, we explore the previous syntheses of these natural products and showcase alternative strategies to access these structures. In chapter 6 we demonstrate the total synthesis of endiandric acid J and beilcyclone A in six and five steps, respectively. The natural products are isolated from the roots of Beilschmiedia erythrophloia as racemates. Our strategy is based on an overall anti–vicinal difunctionalisation of COT through an alkylative anti–SN2’ addition of COT–oxide, followed by a cascade Claisen rearrangement/ 6π electrocyclization reaction. A Wittig olefination and intramolecular Diels Alder reaction afford the natural products.