Synthesis of 3-Methyl-TpMo(CO)2(5-Oxo-Pyranyl) Organometallic Scaffold and Its Application in Forming Quaternary Center at a Ring Junction via an Oxidative Annulation-Demetalation Cascade Open Access

Forsido, Biruk T (2011)

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Due to their versatility, π-allylmolybdenum complexes have become common organometallic enantiomeric scaffolds for the construction of a variety of natural- and non-natural biologically important heterocyclic compounds. Recently, the Liebeskind group has developed a concise, high throughput methodology that is based on oxo- and aza-Achmatowicz reactions, to access both racemic and enantiopure TpMo(CO)2(η3-pyranyl) and TpMo(CO)2(η3-pyridinyl) scaffolds respectively. To probe the use of Achmatowicz reaction in the synthesis of substituted scaffolds and for greater synthetic versatility, 3-methyl substituted TpMo(CO)2(η3-pyranyl) organometallic scaffold has been prepared.

The direct nucleophilic functionalization of charge neutral TpMo(CO)2(η3-pyranyl) and TpMo(CO)2(η3-pyridinyl) complexes complement the nucleophilic functionalization of cationic, highly electrophilic molybdenum complexes. The 3-methyl substituted TpMo(CO)2(η3-pyranyl) scaffold underwent an uncatalyzed Friedel-Crafts-like direct nucleophilic functionalization with silyl enol ether to form a 2,3-disubstituted η3-allylmolybdenum complex. In addition, 2,3-disubstituted η3-allylmolybdenum complexes were obtained in modest yields by addition of organometallic reagents to a cationic molybdenum complex.

Mild and efficient demetalation of η3-allymolybdenum complexes is a key step to convert the intermediate into useful organic compounds. Expanding the scope of annulative demetalation of η3-allymolybdenum to 2,3-disubstituted η3-allylmolybdenum complexes led to the formation of a quaternary center at the ring junction of cis-fused heterocyclic ring system.

Synthesis of 3-Methyl-TpMo(CO)2(5-Oxo-Pyranyl) Organometallic Scaffold and Its Application in Forming Quaternary Center at a Ring Junction via an Oxidative Annulation-Demetalation Cascade
Biruk Teketel Forsido
B.S., Indiana University-Purdue University Indianapolis, 2008
Advisor: Lanny S. Liebeskind, Ph.D.
A thesis submitted to the Faculty of the James T. Laney Graduate
School of Emory University in partial fulfillment
of the requirements for the degree of
Master of Science
Department of Chemistry
Graduate School of Arts and Sciences

Table of Contents

Table of Contents
Chapter One: Introduction to Organometallic Enantiomeric Scaffolding and Synthesis of 3-Methyl Substituted Pyranyl Organometallic Scaffold


Organic Enantiomeric Scaffolding...2
Organometallic Enantiomeric Scaffolding...5
Hydrotris(pyrazolyl)borate (Tp) Ligand in η3-allylic molybdenum complexes...6
Preparation of η3-Allyl Molybdenum Complexes...7

Results and Discussions...13

Synthetic Route to 4-Methyl Furfuryl Alcohol...13
Synthesis of 3-Methyl-5-Oxo-Pyranyl Molybdenum Scaffold...15


Chapter Two: Nucleophilic Functionalization of TpMo(CO)2(η3-pyranyl) Complexes


Nucleophilic Functionalization of Cationic Molybdenum Complexes...26
Direct Nucleophilic Functionalization of η3-Allylmolybdenum Complexes...27

Results and Discussions...30

Chapter Three: Quaternary Center Formation via Oxidative Annulative Demetalation Cascade


Demetalation Approaches Involving Cationic Molybdenum Complexes...45
Demetalation Approaches Involving Charge Neutral Molybdenum Complexes...47

Results and Discussions...49

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