[5+2] Cycloadditions to Form Oxobicyclo[3.2.1]octanes Open Access

Bolton, Emily Nora (2010)

Permanent URL: https://etd.library.emory.edu/concern/etds/pr76f4081?locale=en
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Abstract

Organometallic scaffolds have been studied for alternative strategic and structural approaches to enantiomeric bond construction. These scaffolds may be used to synthesize a variety of natural products such as Bao Gong Teng A. Over the past 20 years the Liebeskind lab has focused on one such scaffold, TpMo(CO)2(η3-oxopyranyl) (Tp=hydridotrispyrazolylborato). In this thesis, an analogous tungsten complex, TpW(CO)2(η3-oxopyranyl), has been explored for the purpose of scientific curiosity. The η3-oxopyranyltungsten scaffold was synthesized in three steps: Achmatowicz oxidative rearrangement of furfuryl alcohol, acetylation of the intermediate , and finally oxidative addition of the substrate to the metal. The reactivity of the resulting η3-oxopyranyltungsten scaffold was studied through Lewis acid mediated [5+2] cycloadditions. It was observed that the synthesis of the TpW(CO)2(η3-oxopyranyl) scaffold was higher yielding than its molybdenum counter-part, TpMo(CO)2(η3-oxopyranyl) scaffold. Additionally, an unusual Friedel-Crafts product was formed after Grignard reagent addition and in a few of the [5+2] cycloaddition examples.

Table of Contents

Introduction

Results and Discussion

Tungsten zero-valent sources

Preparation of the η 3-5-oxo-pyranyl tungsten scaffold

Synthesis of η 3-5-hydroxy-5-methyl (or phenyl)pyranyl tungsten compound

Synthesis of the fully unsaturated tungsten scaffold

Synthesis of a variety of [5+2] cycloadducts

Synthesis of the enantiomeric TpW(CO)2( η 3-oxopyranyl) Scaffold

Spectral property differences between molybdenum and tungsten scaffolds

Conclusion Experimental

Methods and materials

Tungsten metallation sources

Synthesis of the racemic tungsten oxopyranyl scaffold

Synthesis of the enantiomerically pure tungsten oxopyranyl scaffold

Synthesis of (±)-Dicarbonyl[hydriotris(1-pyrazolyl)borato][ η -(2,3,4)-5-methyl-5-hydroxy-2H-pyran-2-yl]tungsten

Synthesis of (±)-Dicarbonyl[hydriotris(1-pyrazolyl)borato][ η -(2,3,4)-5-phenyl-5-hydroxy-2H-pyran-2-yl]tungsten

Synthesis of Dicarbonyl[hydridotris(1-pyrazolyl)borato][ η -(2,3,4)-5-methyl-2H-pyran-2-yl]tungsten

Synthesis of Dicarbonyl[hydridotris(1-pyrazolyl)borato][ η -(2,3,4)-5-phenyl-2H-pyran-2-yl]tungsten

Synthesis of [5+2] Cycloaddition Products

References

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