Synthesis of septanose glycals and progress towards endo-mode cyclization of polyepoxides Open Access

Ephron, Andrew (Spring 2018)

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Septanose glycals have successfully been synthesized starting from both lyxose and ribose. These structures were accessed in 4 steps from pentose starting materials yielding 3,4 benzylidene septanose glycals. X-ray crystallography shows an unanticipated epimerization of the cis-benzylidene to the more stable trans-benzylidene. This has been shown to occur during the Bestmann-Ohira homologation. Glycosylations using various sources of electrophilic iodine and Brønsted acid activators of ribose and lyxose based septanose glycals are described.

            Attempts to synthesize a tetraene precursor of the DE ring sector of brevenal via a series of Grignard and Claisen rearrangement reactions were made. However, due to E/Z selectivity difficulties, other methods were explored. Julia coupling of two sulfone/aldehyde pairs were eventually successful in forming the desired tetraene product. Oxidations of the tetraenes were then explored. Lewis acid catalyzed epoxide cascades were also attempted on model systems.

Table of Contents

Table of contents

Chapter 1: Synthesis of Septanose glycals

Introduction                                                                                                                1

Results and discussion                                                                                                7

Conclusions                                                                                                                12

Chapter 2: Progress towards endo-mode cyclizations of polyepoxides

Introduction                                                                                                                13

Results and discussion                                                                                                23

Conclusions                                                                                                                32

Chapter 3: Experimental procedures                                                                          35       

Chapter 4: References                                                                                                 72

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