Asymmetric Synthesis of Organophosphates and Their

Home , Phosphinate, Phosphoramidate, Phosphoramide, Thiophosphate, Thiophosphoryl chloride

ASYMMETRIC SYNTHESIS OF ORGANOPHOSPHATES AND THEIR

DERIVATIVES

Thesis

Submitted to

The College of Arts and Sciences of the

UNIVERSITY OF DAYTON

In Partial Fulfillment of the Requirements for

The Degree of

Master of Science in Chemistry

Batool J. Murtadha

Dayton, Ohio

May 2020 ASYMMETRIC SYNTHESIS OF ORGANOPHOSPHATES AND THEIR

DERIVATIVES

Name: Murtadha, Batool J.

APPROVED BY:

______Jeremy Erb, Ph.D. Research Advisor Assistant Professor Department of Chemistry University of Dayton

______Vladimir Benin, Ph.D. Professor of Chemistry Department of Chemistry University of Dayton

______Justin C. Biffinger, Ph.D. Committee Member Assistant Professor Department of Chemistry University of Dayton

ii © Copyright by

Batool J. Murtadha

2020

iii ABSTRACT

ASYMMETRIC SYNTHESIS OF ORGANOPHOSPHATES AND THEIR

DERIVATIVES

Name: Murtadha, Batool J. University of Dayton

Advisor: Dr. Jeremy Erb

Organophosphorus compounds (OPs) are widely used in the agricultural industry especially in the pesticide market. Phosphates play a huge role as

biological compounds in the form of energy carrier compounds like ATP, and medicine as

antivirals. OPs have become increasingly important as evidenced by the publication of new

methods devoted to their uses and synthesis. These well-established studies lay the basis

for industrial organic derivatives of phosphorus preparations. The current work explored

methods of synthesizing chiral organophosphate triesters. We experimented with different

processes roughly divided into either an electrophilic or nucleophilic strategy using chiral

Lewis acids, organocatalysts (HyperBTM), activating agents, and chiral auxiliaries with

the goal of control stereoselectivity. These methods were explored through the use of

different starting materials like POCl3, triethyl phosphate, methyl phosphordichloradate, and PSCl3.

My research results suggest that most of the reactions only went to partial

completion. Furthermore, most of the experiments were either non-effective product or the

scientific data were not productive in the reaction, in fact, the product could not be isolated

iv or purified. The synthesis reaction steps were evaluated through TLC, 1H NMR, and 31P

NMR.

v ACKNOWLEDGMENTS

Foremost, I would like to express my sincere gratitude to my advisor Dr. Jeremy

Erb for the continuous support of my master's study and research, for his patience, motivation, enthusiasm, and immense knowledge. His guidance helped me all the time in research and writing of this thesis. Besides my advisor, I would like to thank the rest of my thesis committee: Dr. Vladimir Benin and Dr. Justin C. Biffinger for their encouragement.

I would also like to thank the University of Dayton and, specifically, the

Department of Chemistry for their advice and aid as I performed this research. Thank you to others who helped me with obscure questions, instrumentation issues, and simply listened to me complain as my research progressed.

I wish to thank all the people whose assistance was a milestone in the completion of the thesis. Also, I would like to thank my friends and My colleagues at the chemistry department, who have supported me and had to put up with my stresses and moans for the past three years of study.

Last but not the least, I would like to thank my family: my parents who supported me and offered deep insight into the study and always were by my side and motivate me through the hard nights.

vi TABLE OF CONTENTS

ABSTRACT ...... iv

ACKNOWLEDGMENTS ...... vi

LIST OF FIGURES ……………………………………………………………………...xi

LIST OF TABLES ...... xv

LIST OF ABBREVIATION ...... xvi

CHAPTER ONE INTRODUCTION ...... 1

1.1 Nomenclature of Organophosphorus Compounds ...... 1

1.2 Industrial Importance Of Organophosphorus Compounds ...... 2

1.2.1 Pesticides...... 2

1.2.2 Nerve-Agents ...... 3

1.2.3 Fertilizers ...... 4

1.3 Medical Importance of Organophosphorus Compounds ...... 5

1.3.1 The Role of Phosphorus in Biology ...... 5

1.3.2 Medicines That Use Organophosphorus Compounds...... 7

1.4 General Synthetic Methods to Control Chirality ...... 10

1.4.1 Lewis Acid Catalysis ...... 10

1.4.2 Organocatalytic ...... 13

1.4.3 Chiral Auxiliaries ...... 14

1.5 Methods to Synthesize Organophosphorus Compounds ...... 15

1.5.1 Synthesis Of P(V) Species ...... 15

1.5.2 Other OP Synthetic Reactions ...... 18

vii 1.5.3 Tf2O Activating Regent of Phosphorus (V) Starting Material ...... 20

1.6 Methods to Synthesize Chiral Organophosphorus Species ...... 21

1.6.1 Palladium-Catalyzed Cross-Coupling ...... 21

1.6.2 Biomaterial Methods ...... 25

1.6.3 Electrophilic Phosphorus ...... 26

1.7 Previous Work ...... 28

CHAPTER TWO RESULTS AND DISCUSSION ...... 30

2.1 Attempted Synthesis of 3,5-dimethoxyphenyl (4-methoxyphenyl)

(4-benzyl-2-oxazolidine-3-yl) phosphonate, 4...... 30

2.2 Attempted Synthesis of 4-benzyl-2-oxooxazolidin-3-yl ethyl methyl

phosphate, 6 ...... 36

2.3 Attempted Synthesis of 4-benzyl-2-oxazolidin-3-yl methyl phenyl

phosphate, 13 ...... 40

2.4 Attempted Synthesis of 4-benzyl-2-oxazolidin-3-yl ethyl phenyl

phosphate, 19 ...... 41

2.5 Attempted Synthesis of ethyl methyl phenyl phosphorothioate, 23…………...43

CHAPTER THREE EXPERIMENTAL ...... 47

3.1 Reagents ...... 47

3.2 The Synthesis of Chiral Organophosphate from POCl3 ...... 48

Distillation of the Phosphorus Oxychloride, 1 ...... 48

3.2.1 The Synthesis Of 3,5-Dimethoxyphenyl (4-Methoxyphenyl) (4-Benzyl-2-

Oxazolidin-3-yl) Phosphonate, 4 ...... 48

3.2.2 The Synthesis of 4-Benzyl-2-Oxazolidin-3-yl Ethyl Methyl

viii Phosphate, 6 ...... 52

3.2.3 The Synthesis Of 4-Benzyl-2-Oxazolidin-3-yl Decyl Methyl

Phosphate, 10 ...... 58

3.3 The Synthesis Of P-Chiral Organophosphates From Alkyl Phosphorus ...... 60

3.3.1 The Synthesis Of 4-Benzyl-2-Oxazolidin-3-yl Methyl Phenyl

Phosphate, 13 ...... 60

3.3.2 The Synthesis of Benzyl Ethyl Methyl Phosphate, 16 ...... 64

3.4 Synthesis Of P-Chiral Organophosphates In Presence of Trialkyl Phosphorus

and Tf2O/Pyridine ...... 66

3.4.1 The Synthesis of 4-Benzyl-2-Oxazolidin-3-yl Ethyl Phenyl

Phosphate, 19 ...... 66

3.4.2 The Synthesis of Benzyl Ethyl Phenyl Phosphate, 24: ...... 67

3.5 Synthesis of P-Chiral Thiophosphate ...... 69

REFERENCES ...... 72

APPENDIX A - 31P NMR Distilled Phosphorus Oxychloride ...... 81

APPENDIX B - 31P NMR result from reaction 1 from table 1 ...... 82

APPENDIX C - 31P NMR result from reaction 2 from table 1 ...... 83

APPENDIX D - 31P NMR result from reaction 1 in table 2 (in THF) ...... 84

APPENDIX E - 31P NMR result from reaction 3 in table 2 (in DCM) ...... 85

APPENDIX F - 31P NMR result from reaction 4 in table 2 (Proton Sponge®) ...... 86

31 APPENDIX G - P NMR result from reaction 1 in table 3 using Mg(TfO)2 ...... 87

31 APPENDIX H - P NMR result from reaction 2 in table 3 using TiO2 ...... 88

31 APPENDIX I - P NMR result from reaction 3 in table 3 using AlCl3 ...... 89

ix APPENDIX J - 31P NMR result from reaction 1 in table 4 (BuLi)...... 90

APPENDIX K- 31P NMR result from reaction 2 in table 4 (MeMgCl) ...... 91

31 APPENDIX L - P NMR result from reaction 1 table 5 (left), Mg(TfO)2 ...... 92

31 APPENDIX M- P NMR result from reaction 2 in table 5 (middle), TiO2 ...... 93

31 APPENDIX N - P NMR result from reaction 3 in table 5 (right), AlCl3 ...... 94

APPENDIX O - 31P NMR Phenyl dichlorophosphate ...... 95

APPENDIX P - 31P NMR result from reaction 1 table 6 in BuLi...... 96

APPENDIX Q - 31P NMR result from reaction 2 table 6 in MeMgCl ...... 97

APPENDIX R - 31P NMR Triethyl phosphate ...... 98

APPENDIX S - 31P NMR result of the benzyl ethyl phenyl phosphonate ...... 99

APPENDIX T - 31P NMR Phenyl phosphorodichloridothioate ...... 100

APPENDIX U - 31P NMR result of the ethyl methyl phenyl phosphorothioate in

HyperBTM ...... 101

APPENDIX V - 1H NMR result of the reaction 1 table 2 ...... 102

APPENDIX W - 1H NMR result of reaction 1 table 4 ...... 103

APPENDIX X - 1H NMR result of reaction 2 table 4 ...... 104

APPENDIX Y - 1H NMR result of reaction 1 from table 6...... 105

APPENDIX Z - 1H NMR result of the product 26 ...... 106

x LIST OF FIGURES

Figure 1. Examples of organophosphorus compounds...... 1

Figure 2. Parathion and glyphosate as examples of organophosphorus insecticides ...... 2

Figure 3. Phosphorylation mechanism of ATP ...... 6

Figure 4. Protide strategy with sofosbuvir, is reproduced from a mechanism of

phosphonamidite cleavage 30 ...... 9

Figure 5. Antiviral agents of non-chiral phosphorus ...... 10

Figure 6. the Lewis acid interacting in a nonconstructive way with the diene aiding in

catalyzing the desired reaction...... 11

Figure 7. Diels-Alder reaction and using AlCl3 catalyst to synthesize

organophosphorus reagents using dimethyl chlorine (DCM) as a solvent in

room temperature. reproduced from Said N.41 ...... 11

Figure 8. Triflate Salt (TiCl4) promoted Mukaiyama aldol reaction between

trihydrosilyl enol ether and formaldehyde.43 ...... 12

Figure 9. A mechanism of using metal phosphate in HDA reaction for stereo control ... 13

Figure 10. Organocatalytic fluorination reaction of acid chlorides ...... 14

Figure 11. The structures of several chiral auxiliaries ...... 15

Figure 12. Michaelis-Arbuzov reaction ...... 16

Figure 13. Mcguigan methodology to synthesis phosphoramidate...... 17

Figure 14. Examples of phosphorothioates molecules...... 18

Figure 15. Direct coupling of thiols with H-phosphonates ...... 18

Figure 16. Esterification of H-phosphinic acid using orthosilicates ...... 19

xi Figure 17. Esterification of H-phosphine using orthosilicates ...... 20

Figure 18. Activation strategy from Huang Et Al...... 20

Figure 19. Reaction mechanism adopted from Hunarg et al...... 21

Figure 20. Suzuki-Miyaura cross-coupling reaction ...... 22

Figure 21. Palladium catalyst reaction ...... 23

Figure 22. The use of palladium acetate as a catalyst with ligand through

cross-coupling 65 ...... 23

Figure 23. Literature preparation of menthyl phenyl H-phosphinate ...... 24

Figure 24. Direct reaction of H-phosphinic acid ...... 24

Figure 25. The Corey–Kim oxidation reaction ...... 24

Figure 26. Synthesis a chiral nerve agent using PTE ...... 25

Figure 27. Non-Catalytic method to synthesize phenyl phosphorotriester derivatives ... 27

Figure 28. DiRocco strategy of using NMI as catalyst71 ...... 27

Figure 29. Reaction strategy of Lewis metal catalyst ...... 28

Figure 30. Example of the nucleophilic tertiary amine ...... 29

Figure 31. Synthetic sequence for the preparation of 3,5-dimethoxyphenyl (4-

methoxyphenyl) (4-benzyl-2-oxazolidine-3-yl) phosphonate ...... 31

Figure 32. The reaction sequence for the synthesis 4-benzyl-2-oxazolidin-3-yl decyl

methyl phosphate ...... 38

Figure 33. The reaction of synthesis 19, using triethyl phosphate as starting material ... 42

Figure 34. The two-steps substitution sequence for the synthesis of benzyl ethyl

phenyl phosphate ...... 42

Figure 35. Tetraethyl Diphosphate...... 43

xii Figure 36. The synthesis of ethyl methyl phenyl phosphorothioate – attempt one ...... 43

Figure 37. The synthesis reaction of ethyl methyl phenyl phosphorothioate

- attempt two ...... 44

Figure 38. The multi-step sequence for the synthesis of 3,5-dimethoxyphenyl (4-

methoxyphenyl) (4-benzyl-2-oxazolidine-3-yl) phosphonate ...... 48

Figure 39. The use of Lewis acid metal catalyst to synthesis 3,5-dimethoxyphenyl (4-

methoxyphenyl) (4-benzyl-2-oxazolidine-3-yl) phosphonate ...... 51

Figure 40. The synthesis of 4-benzyl-2-oxazolidin-3-yl ethyl methyl phosphate

– attempt one ...... 52

Figure 41. The synthesis of 4-benzyl-2-oxazolidin-3-yl ethyl methyl phosphate

– attempt two ...... 54

Figure 42. The synthesis of 4-benzyl-2-oxazolidin-3-yl ethyl methyl phosphate, using

Lewis acid metal catalyst ...... 56

Figure 43. The synthesis of 4-benzyl-2-oxazolidin-3-yl decyl methyl phosphate ...... 58

Figure 44. The synthesis of 4-benzyl-2-oxazolidin-3-yl methyl phenyl phosphate -

attempt one ...... 60

Figure 45. The synthesis of 4-benzyl-2-oxazolidin-3-yl methyl phenyl phosphate -

attempt two ...... 62

Figure 46. The synthesis of benzyl ethyl methyl phosphate ...... 64

Figure 47. The synthesis of 4-benzyl-2-oxazolidin-3-yl ethyl phenyl phosphate,

forming phosphoryl pyridin-1-ium intermediate ...... 66

Figure 48. The reaction of synthesis benzyl ethyl phenyl phosphate, step a and

step b in first step substitution ...... 67

xiii Figure 49. The reaction of synthesis benzyl ethyl phenyl phosphate, step a and

step b all two-steps substitution ...... 68

Figure 50. The synthetic sequence for ethyl methyl phenyl phosphorothioate

- attempt one ...... 69

Figure 51. The reaction of synthesis ethyl methyl phenyl phosphorothioate

- attempt two ...... 70

xiv LIST OF TABLES

Table 1: The 31PNMR (ppm) chemical shifting of the reactions using different

base and solvent ……………………………………………………..………...32

Table 2: The 31PNMR (ppm) chemical shifting of the reactions using different

base and solvent for synthesis 4...……………………………………………..34

Table 3: A list of the reactions using different lewis acid metal catalyst …………..……..35

Table 4: A list of the reactions using different alkyl groups, base and solvent

with the 31PNMR (ppm) chemical shifting for synthesis, 6 ……………...…….37

Table 5: A list of the reactions using different lewis acid metal catalysts……….…..……39

Table 6: A list of reactions using different starting material with chiral auxiliary

and an alkyl group ……………………………………………….………..….40

xv LIST OF ABBREVIATION

Abbreviation Compound Name Molecular Formula

31P NMR Phosphorus-31 nuclear magnetic resonance

1H NMR Proton nuclear magnetic resonance

Ac Acetyl CH3CO Ach Acetylcholine Ache Acetylcholinesterase ADP Adenosine Diphosphate

Ar Aryl C6H5 ATP Adenosine Triphosphate

Bn, Bzl Benzyl C6H5CH2

Bu, N-Bu N-Butyl C4H9

Buli Butyllithium C4H9Li

CDCl3 Chloroform-D CDCl₃ Clas Chiral Lewis Acids DABCO 1,4-Diazabicyclo[2.2.2]Octane

DCM Dichloromethane CH2Cl2 DMAP 4-Dimethylaminopyridine DNA Deoxyribonucleic Acid

Et Ethyl C2H5

EtOH Ethanol C2H6OH GC/MS Gas Chromatography/Mass Spectroscopy MeMgCl Methyl Magnesium Chloride CH3MgCl HPLC High Pressure Liquid Chromatography Me Methyl CH3

xvi MeOH Methanol CH3OH OPs Organophosphorus

Ph Phenyl C6H5

Proton Sponge 1,8- C14H18N2 Bis(dimethylamino)naphthalene PTE Phosphotriesterase

Py Pyridine C5H5N RNA Ribonucleic Acid

TEA Triethylamine N(CH2CH3)3

Tf2O Trifluoromethanesulfonic (CF3SO2)2O anhydride THF Tetrahydrofuran C4H8O

xvii CHAPTER ONE

INTRODUCTION

1.1 Nomenclature Of Organophosphorus Compounds

Organophosphorus compounds (OPs) are known as a wide class of chemical compounds where a central phosphorus atom is bound to sulfur, oxygen, or nitrogen linkages with hydrocarbon attachments or to carbon itself. OPs contain a variety of structures that can be listed into two main groups based on the oxidation state of phosphorus, namely phosphorus (III) and phosphorus (V) compounds. Phosphorus (III) centers are known as phosphines and the molecules have the generic molecular formula

R3P. Additionally, there exists separate nomenclature for phosphorus (III) centers that

connect to nitrogen groups, with phosphoramide having a formula (OR)2PNR2 and

phosphorodiamidates having a formula PR2(NR2). Structures of some of these compounds are shown below in Figure 1.

Figure 1. Examples of organophosphorus compounds.

1 1.2 Industrial Importance Of Organophosphorus Compounds

1.2.1 Pesticides

A pesticide can be identified as a substance that contains a chemical and biological

agent that targets pests like insects, mold, mildew, or other undesired biological

organisms.1

Pesticides are a largest sector for a range of countries,with their high production in Asian

countries like China and India. 44% of pesticides are used as insecticides in worldwide usage.2 About 90% of households in the United States use pesticides. Organophosphorus pesticides are known to be widely used, such as insecticide, which has many different compounds, including parathion, malathion and diaznon. While glyphosate is another example of herbicide pesticides. as shown in Figure 2.3

Figure 2. Parathion and glyphosate as examples of organophosphorus insecticides

The United States Environmental Protection Agency (EPA) has stated4 there is a

great deal of interest in the treatment and removal of pests, since these pests can cause and

spread diseases. Pesticides have present a multiple of primary benefits, such as improving

productivity, increase the quality of food, improve weed control to reduce the losses from

the weeds, diseases and help to increase the concentration of antioxidant in fruits that act

as an anti-cancer reagent. 5 However, OPs have been identified as highly toxic causing 2 poison and increase the risk of having cancer. The international agency for research and

cancer (IARC), presents five different organophosphates that have been assessed and documented.6 Pesticides can have negative side effects such as high off-target toxicity to

humans and other species.7,8 Many of the pesticides can be classified into the chemical

groups, organochlorines, organophosphates, and carbamates.9 Those groups can operate

through inhibiting the enzyme acetylcholinesterase, that can cause acetylcholine to transfer

nerve impulses indefinitely and causing symptoms such as weakness or paralysis.10

Organophosphate pesticides can be quite toxic, which is why it has been replaced in some

instances by less toxic carbamates.4

1.2.2 Nerve-Agents

OPs have also been used as nerve gases. One of the first was discovered back in the

1930s by the German chemist Gerhard Scharder using ethyl N,N- dimethylphosphoroamidocyanidate (GA).11 12 13 These are lipid-soluble organic compounds that inhibit the enzyme acetylcholinesterase and inhibit nerve-muscle impulse transmission, which causes damage and changes in human behavior and psychology. High exposure can cause a seizure and loss of consciousness which makes it a very toxic synthetic substance.14 The overall effect is an overstimulation of the muscles by the buildup

of the neurotransmitter acetylcholine (ACh). 15

3 1.2.3 Fertilizers

Fertilizers are chemical substances that can be added to the soil to increase its fertility. Most plants require a certain quantity of nutrients to help them complete their life cycle, which can be organic or inorganic. These chemicals are classified in three different groups: primary, secondary, and micronutrients. Primary nutrients include nitrogen (N), phosphorus (P), and potassium (K) and are required in the largest amounts for plant growth.

A plant requires smaller quantities of secondary such as Calcium (Ca), Magnesium (Mg), and sulfur (S) as well as micronutrients that include boron, copper, iron, and manganese in very small amounts.16 Those types of nutrition can be sorted into different types of fertilizers that can be used today such as blood meal, bone meal, and cottonseed meal.

Fertilizers typically contain 11% of phosphorus since it is a primary nutrient and many plants require around 30 µmol/l of phosphorus.17 Phosphorus fertilizers can be derived from two sources; first, they may be extracted from minerals such as fluorapatite

Ca5(PO4)3F by treating phosphate rock with phosphoric acid. The second phase of development is the reaction of phosphoric acid with ammonia, the synthesis of diammonium phosphate (DAP) and monoammonium phosphate (MAP).

4 1.3 Medical Importance Of Organophosphorus Compounds

1.3.1 The Role of Phosphorus in Biology

1.3.1.1 Description of ATP

Phosphorus is vital to all living organisms because it is involved in many life cycles

and plays a major role in cell energy transfer as part of ATP ( adenosine triphosphate). ATP

is a vital form of energy storage in the mitochondria, also called the “powerhouse” of the

cells.18 Many biological functions require energy and in the human body, the main source

of energy is generated by breaking down ATP. ATP is composed of three main

biomolecular parts: ribose, which is the same simple sugar that is similarly found in the

RNA; adenine, which is the base is connected to ribose; and phosphate groups, which are

responsible for making ATP effective at energy storage. ATP gives energy when it

decomposes and releases ADP (adenosine diphosphate) by a hydrolysis reaction.

1.3.1.2 Kinases

Kinases are enzymes that control the activity of certain proteins depending on the

phosphorylation of specific amino acids in the presence of ATP as a source of phosphate.

Kinase proteins have subfamilies that include tyrosine, serine, and threonine kinases. 19 20

The phosphorylation mechanism usually occurs on the amino acid side chain where a

nucleophilic hydroxyl group attacks the phosphate group on the ATP causing a transferring

of the phosphate group to the amino acid chain and resulting in ADP 21, as seen in Figure

There are a large number of kinases that the human genome encodes due to their

control of a multitude of important biological processes such as metabolism, apoptosis,

5 transcription, the functioning of the nervous and immune systems, and many others.

Owing to their role in biology, it is unsurprising that kinases, which depend on the

reactivity of phosphates, are frequently a target for drug therapy and play roles in human

disease.

Figure 3. Phosphorylation mechanism of ATP

1.3.1.3 Phosphorus in DNA

DNA is defined as a repeating long helical chain of nucleotides containing genetic

information. These nucleotides are tethered together through phosphorus linkages as phosphodiester bonds and the entire framework is coiled through hydrogen bonding. These

phosphate linkages also contribute to the stability of the structure of DNA through the

positioning of the hydrophilic and negatively charged oxyanion toward the outside of the

coil. Interestingly, scientists such as Okonogi et al. found that neutralizing the DNA could lead to greater bending capacity, flexibility, and less ridged structuring. 22

6 1.3.2 Medicines that use organophosphorus compounds

OPs have been used in medicine as drugs against osteoporosis, cancer, and viruses.

A complete description of many different types of phosphorus-based medicinal approaches

can be found in Montchamp’s excellent summary works, but a few examples are given

below. 23 Bisphosphonates have been used in clinical studies because of its P-C-P structure

and ability to act as a biomimic. First synthesized by a Russian chemist Menschutkin in

1865 24, Fleisch later discovered that bisphosphate compounds had biological effects such

as the inhibition of calcification at high doses by impeding the formation of calcium phosphate salts and inhibition of bone resorption,25 which make it an important regent in

the treatment of osteoporosis.12 Some of the most significant and recent developments in

OPs in medicine has come from antiviral prodrugs (Sofosbuvir ®) which is currently the

leading treatment for Hepatitis C, although the cure rate is equivalent to 100% when given

with Velpatasvir independently of the genotype of the virus.26 Recent strategies in

medicines like Sofosbuvir® center around circumventing the kinetic rate-determining

monophosphorylation step of a synthetic sugar while also allowing passage into cells, all

of which is made possible by the installation of temporary non-polar protecting groups on

a monophosphorylated prodrug. The deprotection can be controlled by careful selection of

the identity of the protecting groups so that the drug is only released upon delivery to

specific sites in the body.

1.3.2.1 P-Chiral Medicines

Louis Pasteur originally discovered chirality in 1848 when he separated the two

isomers of sodium-potassium tartrate. A chiral molecule is a molecule that has a non-

superimposable mirror image.27 When two chiral molecules are non-superimposable mirror

7 images, (enantiomers) their chirality can be described using R- and S- notation of their chiral centers through the Cahn-Ingold-Prelog rules. Today, chirality is an important dimension in the pharmacology world. Chiral pharmaceuticals are now usually required under US law to be sold as pure stereoisomers to become FDA approved. Other forms of the molecule (such as its mirror image) are usually prohibited since these different forms can have different biological activities despite the fact that many other properties are identical, such as mass, melting point, or boiling point.28 From a practical point of view, a

reliable and inexpensive method to stereo-specifically synthesize molecules is highly

desirable. While there has been a major focus in developing methods that control the

chirality of carbon centers, synthetic operations aimed at directing the chirality of

phosphorus are beginning to receive much more attention. P(III) species are the focus of

several chiral phosphorus compounds.

On the other hand, chiral P(V) molecules have found more use as pharmaceuticals

such as protease inhibitors that mimic peptides and prevent hydrolytic cleavage or pro-

nucleotides. An important new class of prodrugs based on chiral phosphates, like Tenofovir

alafenamide (phosphonamidite of tenofovir) and Sofosbuvir, might be used to treat

hepatitis B virus (HBV), hepatitis C, and HIV.29 Sofosbuvir has also been used to treat the

Zika virus of the Flaviviridae family of viruses.30 Sofosbuvir was based on the ProTide

approach, which was designed to help avoid the slow monophosphorylation step in its

chemical mode of action in vivo, as shown in Figure 4.

Phosphate, in general, is negatively charged at a physiological pH. This means that

a monophosphorylated synthetic sugar, the active form of a ProTide drug Sofosbuvir, has

8 difficulty entering cells and would require endocytosis for entry.31 32 One option is the

formation of labile phosphate esters that would mask the charges and allow transportation

across the cell membrane. Then, the prodrug can be cleaved into the monophosphorylated

synthetic sugar once inside the cell. Consequently, prodrugs can efficiently increase drug

concentrations within the cell, thus enhancing efficacy.33 This approach was built on

similar previous work with chiral pharmaceuticals based on the CycloSal tactic.34 Because these medicines are sometimes made without any control of the chirality on phosphorus, even though chirality is important to their functionality, an opportunity exists to design

synthesic methodology for the construction of chiral P(V) centers.

Figure 4. Protide strategy with sofosbuvir, is reproduced from a mechanism of phosphonamidite cleavage 30

1.3.2.2 Non-Chiral Medicines With Phosphorus

Phosphorus has played a significant role in non-chiral medicines as it can be used as an active ingredient, drug counterion, and as an excipient. Historically, it is common to use as an excipient in treatments for maladies like chronic kidney disease (CKD).35

Adefovir dipivoxil is used to treat HBV infections since 2002,36 while Tenofovir disoproxil

9 is used since 2001 for the treatment of HIV infections, later in 2008 was approved to be given to patients to treat chronic HBV infections.37 These molecules are shown in Figure

Figure 5. Antiviral agents of non-chiral phosphorus

1.4 General Synthetic Methods To Control Chirality

1.4.1 Lewis Acid Catalysis

A catalyst is a substance that facilitates a chemical pathway taking place by

decreasing the activation energy of the process. Catalysts in organic synthesis can be metal, enzymatic and organic. Lewis acid catalysis has a long history in the synthesis of chiral organic products, such as catalytic asymmetric aldol reaction.38 Lewis acid catalysis

frequently employs a certain metal as a metal catalyst center and commonly operate by

improving the reactivity of the electrophile.39 Those metal atoms form an adduct with a

lone pair bearing electronegative atom within the electrophile, commonly with oxygen or

nitrogen. Lewis acid catalysis has played a huge role in organic synthesis since it counts as

one of the best methods used to control the chirality reactions.

An example of Lewis acid catalysis reaction is shown below (Figure 6). The Diels-

Alder reaction uses AlCl3, a common Lewis Acid catalyst, with/AlMe3/AlClEt2 10 a conjugated diene and a substituted alkene (the dienophile). The aluminum was used to improve the reaction no heat, and lowering the temperature (room temperature to -78° C)

40 41 of the reaction and saw the yield has increased from 20% to 97%.

Figure 6. the Lewis acid interacting in a nonconstructive way with the diene aiding in catalyzing the desired reaction.

Figure 7. Diels-Alder reaction and using AlCl3 catalyst to synthesize organophosphorus reagents using dimethyl chlorine (DCM) as a solvent in room temperature. reproduced from Said N.41

Another example of Lewis acid catalysis is the Mukaiyama aldol reaction discovered by Mukaiyama42. It involves the addition of enol to a carbonyl in the presence of the Lewis acid TiCl4 to form a C-C bond between the two molecules. This type of reaction can be performed in the presence of the chiral ligand and triflate salt as shown in Figure 8.

Figure 8. Triflate Salt (TiCl4) promoted Mukaiyama aldol reaction between trihydrosilyl enol ether and formaldehyde.43

Developing a method that uses chiral controller system with Lewis acid catalysis would be important to impart stereoselectivity to the reaction. A Diels-Alder reaction was first reported reaction that represents of an acrylate ester of 8-phenylmenthol ester reacted with cyclopentadiene and AlCl3 catalysis, in the result of catalyst binding to acryl carbonyl

at the lone pair anti to nitrogen, fixing the acryl group stereochemistry conformation,

besides of the stereochemistry of the aldol reaction giving a yield > 90%. 44

Bin Liu and his team reported a particularly interesting chiral silver phosphate

(metal phosphate) catalyst that used a Hetero-Diels-alder (HDA) reaction to generate a high enantioselective piperazine derivative. (Figure 9) They did investigate a reaction of an azo-

HDA of diazene compounds (2,4-hexadiene) with dienes compounds (urea-based dienophile) at -40 °C using different metal phosphate. Their study shows a table of investigating of BINOL-derives, those derive chiral phosphoric acid showed unless a considerable catalytic activity but with poor enantioselectivity, or others gave 74% yield with 50% ee. 45

Figure 9. A mechanism of using metal phosphate in HDA reaction for stereo control

Their work did involve other metals beside silver, including, magnesium, calcium, and gold phosphates, to catalyze the HDA reaction but without any stereoselectivity. The result of their work have proven that silver phosphate was the one allowed the reaction to proceed with a high 97% ee than the other metals. Their work also shows the role of the diazene compound could play the main role in control reactivity of the reaction.

1.4.2 Organocatalytic

Organocatalytic are catalysts that use small organic molecules to help activate substrates or provide stereochemical information.46 These catalysts traditionally are either nucleophilic, employing a heteroatom as a nucleophilic center, or electrophilic and promote reactions through non-covalent interactions such as hydrogen-bonding.47 As an example,

Paull et. al used a chiral organocatalytic based on the chemical structures of quinine and quinidine in an asymmetric fluorination process. The chiral alkaloid was used in its acylated form (BQ or BQd) and reacted with the acid chloride to form a covalently bond

13 and activated ketene enolate that was fluorinated in very high selectivity (99% or greater)

with excellent yields. An example is shown below in Figure 10.

Figure 10. Organocatalytic fluorination reaction of acid chlorides

1.4.3 Chiral Auxiliaries

The chiral auxiliary is a temporary asymmetric unit that can be attached to the target

substrate in the synthesis of enantiomerically pure compounds. Ideally, chiral auxiliaries

are easy to attach and remove, and induces its chirality efficiently. This class of compounds

can be found easily as many of the chiral auxiliaries are cheap, widely available, and can be sourced from the natural environment. Several examples are shown in Figure 11. The use of a chiral auxiliary is a powerful approach to control chirality and is still considered one of the most useful tools in asymmetric synthesis. Perhaps the most famous implementation of chiral auxiliaries come from reactions like the aldol reaction and alkylation of enolates. The Evans chiral auxiliaries, discovered in 1981 and based on an

oxazolidinone structure that was derived from amino acids, are possibly the most well-known

of this class along with natural products like menthol.48

14 Figure 11. The structures of several chiral auxiliaries

1.5 Methods To Synthesize Organophosphorus Compounds

1.5.1 Synthesis Of P(V) Species

Since this work is focused on exploring new methods for the synthesis of P(V)

compounds. The Phosphorus (V) species are a large class of OPs that consist of

phosphonates, phosphine oxides, phosphinates, phosphoramidates, phoshoanmidates, and phosphorothioates. Although not comprehensive, several important reactions are discussed

below that served as inspiration for the current work.

1.5.1.1 The synthesis of phosphonates

Synthesizing phosphonates, like many other P(V) species, often relies on inexpensive chlorinated precursors such as phosphorus oxychloride, POCl3. Newer approaches try to

find alternative non-chlorinated starting material for phosphonate synthesis like triethyl

15 phosphate due to the formation of waste products, superior solubility, and considerably

lower toxicity. 49 Phosphonates are one of the largest groups in the phosphorus (V) species known for its wide application in therapeutic drugs and industrial chemicals. 50 The

Michaelis-Arbuzov reaction is one of the methods which works well for phosphonate

synthesis. It was discovered by Michaelis and Kaehne in the late 1800s. The product is useful as a reagent in the Horner-Wadsworth-Emmons reaction.51 This method can be

extended to use alcohol by replacing the hydroxyl group with a halogen direct the synthesis

to the desired phosphonates molecule as shown in Figure 12.

Figure 12. Michaelis-Arbuzov reaction

This method involves using primary or secondary alcohol, converting the hydroxyl group to a better leaving group (halide), then treating it with trialkyl phosphate to establish

the P=O bond after an SN2 nucleophilic attack by a halide, converting it to the phosphonate

ester.

1.5.1.2 The synthesis of phosphoramidates

The phosphoramidates are a class of phosphorus (V) compounds that contain two phosphoester linkages in addition to a phosphoramide linkage. Some phosphoramidates have known efficacy as antitumor and antiviral compounds. It does be a part of human cell when it intered, as they tend to find a way to bind to nucleosides that resist viral polymerase

16 in HIV and HBV..52 Importantly, chiral phosphoramidate centers are an essential structural element.

Yue-qing Li and his team did a study on the process of synthesizing phenyl aminoacyl phosphorochloridate involoving amino acid ester (Figure 13) as a key reagent.

An amino acid was exposed to thionyl chloride and alcohol at -10 °C to give the amino acid ester. Then, the resulting compound was treated with triethylamine and phenyl dichlorophosphate in methylene chloride at -70 °C to give the final product after it gets warms to the room temperature and a good yield between 74-85%.53

Figure 13. Mcguigan methodology to synthesis phosphoramidate

1.5.1.3 The synthesis of Phosphates, Thiophosphates, and Thioester Phosphates

The phosphorothioates are compounds that contain three different phosphoroesters as

well as a P=S unit. This type of compound can be found in modern agricultural pest

management and plays an important role in the control of infectious diseases transmitted

by insect vectors and microorganisms. The most famous products are chlorpyrifos and

phoxim. Chlorpyrifos and Phoxim are known for their effects on human health as some of

the studies have to show their effects on rate neuron which make it toxic to human is shown

in Figure 14 54

Figure 14. Examples of phosphorothioates molecules

Yi-Chen Liu and Chin-Fa Lee reported a process for the preparation of phosphorothioesters using N-chlorosuccinimide, as shown in Figure 15. 55 In their study, various halides were tested to produce a high percent of phosphorothioester. N- bromosuccinimide was chosen to be used for the pre-preparation of phosphorothioester over N-iodosuccinimide, as N-iodosuccinimide was used instead of N-chlorosuccinimide, producing the intermediate sulfenyliodide as a highly reactive side product. This would lower the final production of the finished product but would be higher than that of givin by

N-borosuccinimide.

Figure 15. Direct coupling of thiols with H-phosphonates

1.5.2 Other OP synthetic reactions

The esterification reaction is a reaction between an acid and alcohol to produce an ester. In 1960 a synthesis of organophosphorus molecules involved synthesizing methyl and ethyl hypophosphites by Kabachnik.56 This esterification used hypophosphorous acid

18 + – and a strong Bronsted acid-like diazalkanes (R2C=N =N ) with alkyl substitutions (R) of groups of methyl or ethyl, for example.57 58 Following this, Nafan’ev performed the

esterification using the Dean-Stark trap as dehydrative in the acid catalyst reaction, saving

an extra step of drying it later.

Esterification of monosubstituted phosphinic acids, hypophosphorous acid and

hypophosphite salts can also be approached by using orthosilicates. Orthosilicates can be

used to esterify phosphonic acids selectively and in give a high yield of product.

Purification by extraction is simple and orthosilicates are commercially cheap and usable.

This reaction can be performed by adding the orthosilicate to phosphonic acid in toluene

and refluxing the reaction mixture for 24 h under a N2 atmosphere. The reaction is shown

in Figure 16 with R as an alkyl group and R’ can be a phenolic group or alcohol.

Figure 16. Esterification of H-phosphinic acid using orthosilicates

The same method had been applied using hypophosphorous and hypophosphite salt

as it shown in Figure 17. Higher pKa of salt can result in non-reactive phosphonate, which

is valuable using hypophosphite salt because of its low pKa. A number of reactions have

been conducted in the presence of various hypophosphorous orthosilicate compounds in a

variety of solvents taken to reflux temperature in the nitrogen atmosphere and the resulting

compound has been analyzed by 31P-NMR.

Figure 17. Esterification of H-phosphine using orthosilicates

1.5.3 Tf2O Activating Regent Of Phosphorus (V) Starting Material

Recently J. Young Kang reported a new strategy of activating phosphorus that

involves a stepwise substitution reaction of a pre-generated alkyl phosphate triester

electrophile with a nucleophile. The key finding was that the use of triflic anhydride (Tf2O) can phosphorus oxides.59 The formation of an intermediate triflate anhydride is usually

accomplished with a base, in a solvent with cooling or at RT. This intermediate is then

allowed to react with a nucleophile to yield products.

Figure 18. Activation strategy from Huang Et Al.

J. Young Kang has mentioned in his study entitled "Direct Aryloxylation /

Alkyloxylation of Dialkyl Phosphonates for Synthesis of Mixed Phosphonates" is an

excellent chemo-selective method with great tolerance groups. (e.g. ester, acrylate, ether,

and hydroxy groups) that shows a high % yield as an example from ethyl ferulate and

estradiol.60 20 Figure 19. Reaction mechanism adopted from Hunarg et al.

1.6 Methods to Synthesize Chiral Organophosphorus Species

An asymmetric synthesis involves a reaction that creates one or more new stereogenic centers by the action of a chiral reagent or auxiliary. Synthesizing chiral organophosphorus, P-stereogenic, or P-chiral compounds, remain a difficult challenge in organophosphorus chemistry. In the 1970s, the methodology of synthesizing chiral phosphorus was investigated owing to the ability of chiral phosphorus ligands to impart stereocontrol on hydrogenation reactions as shown by the work of Kagan and Knowles.61,62

Chiral auxiliaries are used the most to control stereochemistry at phosphorus centers.

1.6.1 Palladium-Catalyzed Cross-Coupling

Transition metal-catalyzed asymmetric cross-coupling is a possible synthetic strategy for producing chiral OPs. The Suzuki-Miyaura cross-coupling reaction was introduced in 1979. Pd-catalyzed cross-coupling can perform direct allylation of hypophosphorous acids as well as H-phosphonic acid to synthesize phosphinates in the 21 presence of alcohol as shown in Figure 20. The reaction proceeds in excellent yield with

water as the byproduct.63 Although the product contains a P-chiral center, the product in

the example below is produced as a mixture of stereoisomers.

Figure 20. Suzuki-Miyaura cross-coupling reaction

Montchamp and his coworkers performed several reactions using this method using cinnamyl alcohol since it is very reactive when paired with Pd-catalyzed allylation.

Screening of various ligands, solvents, and Pd catalysts was performed by the Montchamp

team to see if they could impact or boost yields. During those reactions, they concluded

that the t-amyl alcohol was found to be the better solvent alternative, since the azeotropic

by-product of the water may be the Dean-Stark trap..64

The first reactions involved using palladium acetate as a catalyst with no ligand,

which resulted in no yield of the desired produect. However, Xantphos [4,5-

bis(diphenylphosphino)-9,9-dimethylxanthene], showed a high yield (around 80%). 1,1’-

bis(diphenylphosphino) ferrocene (DPPF) was tested as a ligand, but the yield was lower

compared to Xantphos. The reaction of using palladium acetate as the catalyst, palladium

chloride, or tris(benzylideneacetone)dipalladium (Pd2(dba)3) as it shown in Figure 21, has

giving a in range of 55-60% yield of the product with palladium chloride having the lowest

yield.

22 Figure 21. Palladium catalyst reaction

This method was later performed using menthyl phenyl-H-phosphinate,

PhP(O)(OMen)H, to synthesize P-stereogenic hydroxymethyl phosphinates as P-stereo genic building blocks. Figure 22

Figure 22. The use of palladium acetate as a catalyst with ligand through cross-coupling 65

Chiral monophosphate ligands are commonly synthesized by using menthol phosphinates as a chiral auxiliary using the Suzuki-Miyaura cross-coupling reaction to synthesize the chiral auxiliary, PhPCl2 and menthol react in the presence of the base

(pyridine) and NaHCO3 with crystallization at -78 °C. (Figure 23) This method suffers

from the problem of difficulty in separating the diastereoisomer products, hence multiple

recrystallizations are needed.

Figure 23. Literature preparation of menthyl phenyl H-phosphinate

Later, Berger and Montchamp were able to find another way to synthesis depending on two key points; the first one as shown in Figure 24, is the simple preparation of easily crystallized (hydroxymethyl) phosphinates. 66

Figure 24. Direct reaction of H-phosphinic acid

The second as it shown in Figure 25, it is the stereoselective cleavage of the hydroxymethyl using the Corey–Kim oxidation to unmask the P(O)H.

Figure 25. The Corey–Kim oxidation reaction

24 1.6.2 Biomaterial Methods

The stereoselective synthesis of organophosphates or thiophosphates using phosphotriesterase (PTE) as a catalyst has been explored. PTE is the best enzyme expressed by Pseudomonas diminuta for the hydrolytic detoxification of organophosphate nerve agents. It can hydrolyze a wide range of organophosphate using a zinc metalloprotein. A team at the University of Texas did a study on how to synthesis a chiral nerve agent using PTE. 67

Figure 26. Synthesis a chiral nerve agent using PTE

25 The nerve agent analogs, like nerve agents, usually do not have pure stereoisomers

available, which is problematic for evaluating protective measures or therapeutics. This led

to developing a synthesis methodology called chemo-enzymatic synthesis. Nitrophenolic

stereoisomers were synthesized without tstereo-control, with the hopes that an enzyme

would be able to hydrolyze specific stereoisomers, leaving the desired target molecule

intact. PTE is capable of achieving very high selectivities in this type of resolution reaction.

Other chemo-enzymatic reactions, like the biocatalytic oxidation of racemic O,S-dimethyl

O-p-nitrophenyl phosphorodithioate, use chloroperoxidase as a catalyst. However, the

reactions are usually extremely limited in scope. 68 An example of this chemistry is shown

below, in Figure 26

1.6.3 Electrophilic Phosphorus

The use of P(V) electrophilic compounds as a building block to construct

organophosphorus compounds has been a popular strategy in the literature.69 There are many different P(V) compounds that could be used, but they frequently originate with

POCl3. For example, Villard et al. used a typical non-catalytic method to synthesize phenyl phosphorotriester derivatives in good yield (63-76%) through use of a phosphorochloridate with an electrophilic P(V) starting material but needed three equivalents of the P(V) phosphorochloridate and six equivalents of N-methyl imidazole (NMI) per equivalent of

the alcohol. 70 Figure 27

26 Figure 27. Non-Catalytic method to synthesize phenyl phosphorotriester derivatives

While Villard’s method did not control the stereochemistry on phosphorus,

DiRocco et al. have reported the use of chiral nucleophilic catalysts with success that

shown in Figure 28. Here, DiRocco used an imidazole-based multifunctional catalyst to

perform phosphoramidation on synthetic sugars.

Figure 28. DiRocco strategy of using NMI as catalyst71

Unfortunately, not only is the catalyst difficult and expensive to synthesize

(requiring separation by preparative chiral SFC), but the work did not demonstrate the

synthesis of a P-(S) stereocenter in high yield and selectivity. Additionally, their reported

yields were not based on isolated chemical yields, but relied on 1H NMR (literature shows

some drastic decreases in yield between NMR yield vs. isolated yield) or HPLC from the crude reaction mixture. Also notable is the requirement to prepare a chlorophosphate

27 starting material in a separate step because it is not commonly commercially available, something that is all too common in the literature.

1.7 Previous Work

Dr. Erb 's work presents the objective of developing a novel method for the construction of a single organophosphate stereoisomer using available synthetic strategies, including organocatalytic and Lewis acid catalysis. Many specific catalysts have been tested. Our study is a continues of Dr. Erb 's work, he has previously researched the use of

POCl3 as a starting material in the presence of Lewis acids such as magnesium and titanium, as an aid in the type of reaction that he has done, a triple susbstitution reaction.

Figure 29 The triple or multi-step reaction is constant of the substitution of a leaving group on the phospours center generating a chiral organophosphate compunds. 72,73

Figure 29. Reaction strategy of Lewis metal catalyst

2+ The Lewis acids TiO2 and Mg are well known to increase the reactivity of the phosphate groups in adenosine triphosphate in a biological environment. (Antilla, 2011) In

Dr. Erb’s work, they also showed evidence of increasing the reactivity of the phosphorus 28 center and ultimately led to an increase in yield of 8-36% comapried to non-catalyst reaction yield.

Figure 30. Example of the nucleophilic tertiary amine

Chiral ligands were also added to these metals in the expectation that they would

be able to regulate the stereoselectivity of the reaction as shown in the literature and as an

indication of the use of BINOL with metal in the HAD reaction. But despite better yields,

only racemic mixtures were observed. In addition, nucleophilic organocatalysts N-methyl

imidazole (NMI) were tested too but did not give an acceptable yield %.

29 CHAPTER TWO

RESULTS AND DISCUSSION

Our experiments centered on finding a mild, efficient, and easy methodology for the synthesis of chiral OPs. Our synthetic experiments centered around two different catalytic approaches: Lewis acid catalysis and organocatalytic. The current body of work was inspired by the synthesis work with organophosphates that has been introduced by

Fisher and Montchamp.

Previous work in our group explored methods to synthesize OPs in a stereospecific manner from the readily available and inexpensive phosphorus oxychloride, POCl3. We

were able to identify catalysts such as MgSO4, that were capable of generating improved

yields of triaryl phosphates, anf give a higher yield than the non-catalyzed reaction. 72

However, in the process of the reaction, the addition of chiral ligands to the Lewis acid

catalyst was unable to imprint stereochemical details on the products. Therefore, we turned

our attention to the use of chiral auxiliaries in the oxazolidinone family.

2.1 Attempted synthesis of 3,5-dimethoxyphenyl (4-methoxyphenyl) (4-benzyl-2-

oxazolidine-3-yl) phosphonate, 4:

We chose to keep the same starting material, POCl3, for our new investigations.

Each chlorine in POCl3 is potentially labile enough to be displaced by nucleophiles, so the

reaction required planning of a three-step substitution sequence. The first substitution reaction between the POCl3 and the chiral auxiliary would be followed with the second and

30 third step substitution of the reaction to produce a chiral phosphorus center, product 4.

(Figure 31) We envisioned that placement of the chiral auxiliary on our substrate would be able to direct future nucleophilic groups onto the phosphorus center. Additionally, if the chiral auxiliary was too labile and easily displaced by nucleophiles, adding it on last might enable a nucleophilic resolution of the resulting diastereomers. There are literature

precedents focused on resolving chiral alcohols in a closely related methodology. We chose

to pair phosphorus oxychloride with (R)-4-Benzyl-2-oxazolidinone because of its historical precedence in enantioselective synthesis.74 Two different phenyl derivatives, p-

methoxyphenol and 3,5-dimethoxyphenol, were chosen because they were affordable and

we had previously been successful with them as nucleophiles when paired with POCl3.

Additionally, the ease of monitoring by thin-layer chromatography (TLC) increased the

appeal of the phenolic derivatives. A general reaction is shown down in Figure 31.

Figure 31. Synthetic sequence for the preparation of 3,5-dimethoxyphenyl (4- methoxyphenyl) (4-benzyl-2-oxazolidine-3-yl) phosphonate

We tested a variety of conditions in this reaction. Different solvents were tested in the

reaction since the solvent can have a high impact on solubility, stability, and reaction rates.

Experience showed that the best solvents to be used were DCM and THF, while the chiral

auxiliary failed to dissolve in the DEE, while when we tried toluene it did give a greasy

31 thick product that was hard to dissolve later in different solvents for isolated in the

chromatography, for example ethyl acetate, ethyl acetate/hexane, and dichloro methane for.

This multi-step sequence was also conducted in the presence of different strong bases, namely n-butyllithium, MeMgCl, and Proton Sponge® (1,8-

31 Bis(dimethylamino)naphthalene). The P NMR spectra of the starting material POCl3

resulted in a single peak δ = 4.84 ppm (Appendix A). The first substitution reaction using

BuLi as a base in THF resulted in new 31P NMR signals with chemical shifts of δ = 6.40

and δ = -1.27 ppm. While using Proton Sponge® as a base in THF, the result crude 31P

NMR showed two peaks at δ = 4.24 ppm which tells there was still starting material that not fully reacted, while the other peak is δ = -5.50 ppm.. This information is summarized in Table 1, shown below.

Table 1: The 31PNMR (ppm) chemical shifts of the reactions, using different base and solvent

Crude Reaction # Chemical Solvent Catalyst Base 31PNMR (ppm) Distilled Phosphorus / / / / 4.84 trichloride (4-benzyl-2-oxazolidine-3- 6.40 1 THF / BuLi yl) phosphonic dichloride -1.27

(4-benzyl-2-oxazolidine-3- Proton 4.24 2 THF / yl) phosphonic dichloride Sponge® -5.50

32 The synthesis of 4 involved three steps substitution , after the first step reaction of

the starting material and the chiral axuilliary have been giving an new chimcal shifts using

both bases (appendix B and C), we took the crude produ to the next step, which was

performed in both THF and DCM, using two the same different strong bases, Proton

Sponge® and BuLi. When the synthesis of 4 was conducted using THF as a solvent and

Proton Sponge® the 31PNMR spectra for the compound 4 in the THF has shown there were

three peaks, one had a chemical shift of 1.99 ppm, and since can’t be related to any of the starting material or final product refrencing to the 1HNMR, we assumed it is a byproduct.

Some of the starting materials (4.95 ppm) were still there and not fully reacted. The shift

at δ = -3.48 ppm probably represents the main product we were trying to synthesize with

the 1H NMR supporting spectrum. Using BuLi resulted in the reaction failing, with no

observable peak of any phosphours compunds in the 31P NMR spectrum. We attempted to

isolate 4 using column chromatography but were unsuccessful, This may be due to a

product that is not stable enough to withstand a silica gel or the combination solution was

not powerful enough to help the product detach the silica gel in the column

chromatography.

The same procedure was followed for the synthesis 4, using DCM as a solvent,

which was used to monitor by 31P NMR the reaction progress. This procedure resulted in

a peak with a chemical shift of δ = -6.55 ppm, in the presence of BuLi as a base. However,

a 31P NMR signal with a shift of δ = -6.01 ppm was observed after the product was washed

using water and exctract in the CH2Cl2, then it dried using sodium sulfate, the solvent

evaporated under reduced pressure, and dissolved in CDCl3 to run in the NMR. This time,

two phosphorus containing species were present using Proton Sponge® as a base, with 33 31P NMR chemical shifts of δ = -3.44 ppm and -6.58 ppm. One of the peaks was probably the product we were trying to synthesize (-3.44 ppm), although it was minor peak comparing to the δ = -6.58 ppm peak. This information is summarized in Table 2. We also examined this reaction in the presence of Lewis acids in conjunction with the chiral auxiliary in our attempts to synthesize 3,5-dimethoxyphenyl (4-methoxyphenyl) (4- benzyl-2-oxazolidine-3-yl) phosphonate 4.

Table 2: The 31PNMR (ppm) chemical shifts of the reactions, using different base and solvent in the synthesis of compound 4.

Reaction 31PNMR Organophosphorus Molecule Solvent Base # (ppm) 3,5-dimethoxyphenyl (4-methoxyphenyl) 4.95 Proton 1 (4-benzyl-2-oxazolidine-3-yl) THF 1.99 Sponge® phosphonate, 4 -3.48

3,5-dimethoxyphenyl (4-methoxyphenyl) NO 2 (4-benzyl-2-oxazolidine-3-yl) THF BuLi PEAK phosphonate, 4

3,5-dimethoxyphenyl (4-methoxyphenyl) -6.54 3 (4-benzyl-2-oxazolidine-3-yl) DCM BuLi -6.57 phosphonate, 4

3,5-dimethoxyphenyl (4-methoxyphenyl) Proton -3.44 4 (4-benzyl-2-oxoxazolidin-3-yl) DCM Sponge® -6.58 phosphonate, 4

34 We then proceeded to switch to the next stage involving Lewis catalytic metal, our

justification for selecting this step as our next in our research was we wanted to better

enable the phosphorous center to manage the three-phase reaction in addition to the cleaner

NMR Spectrum.

Table 3: A list of the reactions using different Lewis acid metal catalyst

Target Crude Reaction Starting Solvent Base Cat. Organophosphate 31PNMR # Material Product (ppm)

3,5-dimethoxyphenyl (4- methoxyphenyl) (4- 1 THF Proton Mg(TfO)2 -6.92 benzyl-2-oxazolidine-3- Sponge® yl) phosphonate

3,5-dimethoxyphenyl Proton (4-methoxyphenyl) (4- 2 THF Sponge TiO2 -7.06 benzyl-2-oxazolidine-3- ® yl) phosphonate

3,5-dimethoxyphenyl Proton (4-methoxyphenyl) (4-

3 THF Sponge AlCl3 -6.90 benzyl-2-oxazolidine-3- ® yl) phosphonate

Thus, we decided to add the catalysts after the first substitution reaction, but

prior to the next two substitution reactions. In this scenario, the nucleophile would build

up in concentration before any reaction took place, causing substitution to occur multiple 35 times once the reaction warmed up and leading to a mixture of products. Each reaction

involved using a different catalyst metal, resulting in Mg(OTf)2 and TiO2 a single sharp

peak at δ = -6.92 ppm and -7.06 in CDCl3, Similarly, catalysis with AlCl3 showed a single

peak at δ = -6.90 ppm. This data is summarized in Table 3.

We tried a variety of workup conditions while trying to isolate NMR peaks that we suspected were the product. In a reaction using Mg(TfO)2, extraction was performed with water and ethyl acetate. The reaction that used TiO2 was run through Combiflash.The

reaction using the AlCl3 was extracted with aqueous NH4Cl and ethyl acetate, then with

saturated sodium bicarbonate, and brine. The organic layer was dried over magnesium/sodium sulfate, filtered, and the solvent was removed with rotary evaporation.

The end result, which was obtained from the 31P NMR spectrum, revealed no peak o

phosphorus for Mg(TfO)2 (appendix G) and TiO2 (appendix H) although AlCl3 (appendix

I) revealed a single stable peak at the final 31P NMR.

2.2 Attempted synthesis of 4-benzyl-2-oxooxazolidin-3-yl ethyl methyl phosphate, 6:

Since compound 4 could not be isolated, we turned our attention to a different

derivative that may prove more stable. Rather than aryl phenolic groups used as

nucleophiles, synthesis using alkyl-based hydroxyl nucleophiles could be better since they

are expected to be better nucleophiles and should be worse leaving groups, once attached.

We chose to test methanol, ethanol, and octanol as potential nucleophiles due to their

commercial availability and low cost. We used the same strategy whereby the chiral

auxiliary would be installed first, followed by methanol and ethanol. Each reaction was

monitored by 31P NMR to monitor the reaction progress.

36 The reaction was also performed with a different order of addition for the nucleophiles using the same standard procedure. Table 5 shows the different reactions, the first starting with the (R)-4-Benzyl-2-oxazolidinone, followed by methanol and ethanol.

While the second was performed starting with methanol, followed by ethanol and (R)-4-

Benzyl-2-oxazolidinone, while atteping reaction 3 of attempt one but with Proton

Sponge® as a base. This information is summarized in Table 4.

Table 4: A list of the reactions using different alkyl groups, base and solvent with the 31PNMR (ppm) chemical shifts for the synthesis of 6

Crude Reaction # Solvent Base 31PNMR (ppm) 2.40 1 THF BuLi 0.03

2 THF MeMgCl -4.97

3 THF Proton Sponge® NO PEAK

The 4-benzyl-2-oxazolidin-3-yl ethyl methyl phosphate 6 molecule, when synthesized in BuLi (base), the result present a two single solid peaks (δ =2.40 ppm) and

(δ =0.03 ppm), neither of those peaks could be the desired product. The peak can be

75 identify of PO(MeO)3 as it recorded in the literature, while the δ = 0.03 could be H3PO4.

37 In the appendix J, a spectrum is also included after the crude reaction was washed with water/CH2Cl2 and sodium sulfate used to dry the organic layer. While appendix K shows the spectrum resulting from ethanol followed by methanol substitution addition step. The use of MeMgCl as base resulted in a chemical shift value of δ = -4.97 ppm for the crude reaction mixture after the three substitutions.

Following the same process, ethanol was replaced by a longer chain of alcohol, such as octanol. (Figure 32) Octanol was treated with Grignard Reagent (MeMgCl) and the reaction was monitored by NMR. After the octane addition and the third substitution, the

31P NMR was taken, no peak was identified. We may infer that the third substitution was not effective, since there was no peak in the 31PNMR.

Figure 32. The reaction sequence for the synthesis 4-benzyl-2-oxazolidin-3-yl decyl methyl phosphate

At the same time, we tested different Lewis acids for two reasons. First, to hold to a reaction using Proton Sponge® expecting this time to give a result of an absolute growth of a peak in the 31P NMR. Second, to reduce the number of peaks of the by-product and cause the electrophile to react completely with the nucleophile. Experiments became involved using methanol and ethanol as nucleophiles, with Lewis acids such as

(Mg(TfO)2, TiO2, and AlCl3, intending to activate the P-center for the multi-step substitution. In the presence of each Lewis acid catalyst, a major peak was observed in each spectrum along with a minor peak. This information is summarized in Table 5. As 38 was the case previously, the resulting compounds could not be isolated regardless of workup conditions.

Table 5: A list of the reactions using different Lewis acid metal catalysts

Target Crude Reaction Starting Organoph Solvent Base Catalyst 31PNMR # Material sphate (ppm) Product

-1.81 Proton 1 DCM Mg(TfO)2 6 -5.79 Sponge®

1.80 Proton 2 DCM TiO2 6 -6.54 Sponge®

1.30 Proton 3 DCM AlCl3 6 -6.38 Sponge®

39 2.3 Attempted synthesis of 4-benzyl-2-oxazolidin-3-yl methyl phenyl phosphate, 13:

A new reaction was performed, this time using phenyl phosphoryl dichloride as a starting material. The reaction is shown below in table 6. All the reactions were performed in a dry solvent with strong bases like n-butyllithium (n-BuLi) or Grignard reagent

(MeMgCl).

Table 6: A list of reactions using different starting material with chiral auxiliary and an alkyl group

Target Crude Reaction Starting Material Solvent Base Organophosphate 31PNMR # Product (ppm) -7.25 -8.57 1 DCM BuLi 13 -10.49 -15.37

2 THF MeMgCl 13 -7.32

The same standard procedure was used, starting with (R)-4-Benzyl-2- oxazolidinone as the first nucleophile followed by methanol. The chemical shift of the starting material in the 31PNMR spectrum appeared at δ = -3.34 ppm. The crude 31PNMR spectrum shows multiple small peaks at δ = -7.25, -8.57, and δ =-15.37, but none of those 40 peaks survived in our attempts to isolate them. whilethe dominant peak at δ = -10.49, did

survive the isolation with a little of chemical shift. (appendix L, M, N ). The 1H NMR

provided some evidence that we made the product as evidenced, but there were extra peaks

indicating byproducts or unreacted material. This information is summarized in Table 6.

The second reaction in Table 6 involved switching the order of the introduction of the nucleophiles, methanol then (R)-4-Benzyl-2-oxazolidinone. The 31P NMR spectrum

after the final reaction, resulted in phosphorous containing compounds with chemical shifts

of δ = -7.32, which was a close chemical shifts to the product of attempt one product (δ =

-7.25), after it was purified and isolated the chemical shift for the 31P NMR finalized with

a new peak chemical shifts at δ = -4.29. We assume the isolation washed away the

molecule that allowed one of the nucleophile to leave the phosphorus core. The successful formation and isolation of the product resulted from either the change in base (from BuLi to MeMgCl) or a change in the order of addition, but it is unclear which were more important. We have not yet been able to determine the effect of the chiral auxiliary on the stereochemistry of the reaction.

2.4 Attempted synthesis of 4-benzyl-2-oxazolidin-3-yl ethyl phenyl phosphate, 19:

Since the results from the use of the POCl3/chiral auxiliary were not successful, a

change a strategy was needed. For this, we turned to Huang and Kang’s triflate activation

strategy.76 This method uses alkyl phosphates as alternative starting materials, another

resone we foolowed this strategy is that the ethyl is a better leaving froup than Cl. the

reaction of Tf2O and pyridine will generate a highly activated phosphorylpyridin-1-ium ion susceptible to nucleophilic attack that replaces one of the alkyl groups temporary.

41 While Huang and Kang’s chemistry are impressive, it does not explore the possibility of

creating P-chiral molecules, as well we believed that the chiral auxiliary should be used in

this technique.

Figure 33. The reaction of synthesis 19, using triethyl phosphate as starting material

We attempted to synthesize two separate products, 4-benzyl-2-oxazolidin-3-yl ethyl phenyl

phosphate and benzyl ethyl phenyl phosphate, using the same method as seen in Figures

34 and 35. That's why we tested separate nucleophiles than chiral to see if the chiral

compound is what's giving us a trouble with isolation. During the reaction, the crude

products were monitored through 13PNMR and GC-MS. (appendix S)

Figure 34. The two-steps substitution sequence for the synthesis of benzyl ethyl phenyl phosphate

We have been successful in synthesizing phenyl diethyl phosphate from both attempts, resulting that any further reactions (third substitution) have been unsuccessful.

42 31PNMR and 1H NMR showed the output of a single peak of 26 compound, as seen in

Figure 36. We have also been able to verify its identification by using GC-MS.

Figure 35. Tetraethyl Diphosphate

2.5 Attempted synthesis of ethyl methyl phenyl phosphorothioate, 23:

Thiophosphoryl chloride (PSCl3) is one of the possible starting materials that may

be used as an alternative to POCl3 and can be relatively stable, easy to purify and produce,

and contains stable phosphorus with three leaving groups present. In Dr. Erb 's lab,

thiophosphate compounds could be synthesized, but there was little improvement in

distinguishing the enantiomers through the HPLC, we thought synthesis various product

will give us a success on the enantiomers separation. Previous studies have shown that the addition of Lewis acid or chiral nucleophilic catalyst is beneficial to organophosphate synthesis (OPs). Nevertheless, these approaches are limited and frequently do not have effective control of phosphorous stereochemistry.

Figure 36. The synthesis of ethyl methyl phenyl phosphorothioate – attempt one

43 We planned to use thiophosphoryl chloride in this model reaction based on previous publications from the Dr. Erb lab and related work with POCl3. The method uses the

electrophilic P(V) compound (PSCl3) reacted with nucleophiles in the presence of pyridine

as a weak base, at -78 °C (under N2) to give a triply substituted thiophosphate triester.

Accurate alcohol compound such as phenol, methanol, and ethanol were used as nucleophiles due to their low cost.

Figure 37. The synthesis reaction of ethyl methyl phenyl phosphorothioate - attempt two

Another reaction was performed in tandem in the presence of an organo-catalyst,

HyperBTM. In both cases, phenol was added as the first nucleophile, followed by ethanol and then finally methanol. The reaction was monitored through 1H NMR and 31P NMR.

The reaction was successful in producing the product, 23, as evidenced by NMR data.

(appendix U) The proton NMR spectrum shows multiple peaks in the expected range for

the phenol group (δ = 7.26 -7.42 ppm), methyl group bonded to an oxygen (δ = 3.82 ppm),

and an ethyl group bonded to an oxygen (δ = 4.43, 1.25 - 1.92 ppm). The 31P NMR shows

some chemical shifts, when compared to the starting material (from 54 ppm for the

PhOPSCl2 to 60-65 ppm for 23). The reaction utilizing HyperBTM yielded the product as

well. Unfortunately, separation of the resulting enantiomers was not possible by HPLC.

The sample was run through a chiral R,R - Whelk -01 column, with 10 μm and 100Å spherical Kromasil silica, plus a variety of mobile phases (ethyl acetate, hexanes,

44 isopropanol, and THF were tested in various combinations) and a RegisPack column using isopropanol and hexanes. Additionally, the sample was shipped to Regis Technologies,

Inc. for separation on their product line but was unsuccessful.

In conclusion, several methodologies for the preparation of triester phosphate have been and continue to be developed. The objective of this research was to develop a new catalytic synthesis of chiral organophosphates. It was hoped that this work will ultimately lead to some convenient method for the stereoselective synthesis of P-chiral organophosphates and their derivatives.

Optimized analysis with various phenyl and alkyl groups has been demonstrated for the synthesis with phosphoroamidate, phosphate and thiophosphate. The POCl3 was one of the key starting materials that required the chiral auxiliary to react in the presence of the base. The chiral compound ((R)-4-Benzyl-2-oxazolidinone) was then intended to guide the stereochemical outcome of potential substitutions and ultimately synthesize chiral OPs in three-steps synthesis. Unfortunately, we were never able to isolate most of our target compounds and fully characterize them.

The challenges experienced during the synthesis of the desired product using p- methoxyphenol and 3,5-dimethoxyphenol were associated with the size of nucleophiles.

Bulky nucleophiles induced a drop in the development of the reaction and no control over stereoselectivity. A less cumbersome and more nucleophilic solution was used by aliphatic substitution. This method has provided improved yields for certain precursors, but again we have not been able to distinguish the products . Although the reaction involving octanol as one of the substitution groups did not survive the last step of the reaction.

45 Different starting materials and pathways have also been investigated, such as triethyl phosphate, where we adopted Huang and Kang's process approach in our hopes of synthesizing chiral OPs. This reaction has been negatively impacted by the production of tetraethyl diphosphate, and we will need to find a way to suppress its formation. The PSCl3 was also investigated with the Organo-Catalytic HyperBTM. We have been able to synthesize and characterize thiophosphate products but have not been able to isolate the resulting enantiomers by HPLC.

Variations in various reaction conditions, such as stirring and temperature, which have a direct effect on the reaction rate, have been studied. Another matter, the use of various bases, BuLi is commercially available but can lose its concentration consistency over time. Though MeMgCl was perceived to be a strong base but noted for its high risk as a drug. Both of these bases have proven their efficacy in the synthesis, but it was difficult to monitor the stereochemistry of the target drug. When transitioning to a weaker base such as pyridine, the result was stronger under both temperature and time conditions.

Overall, we are continuing our efforts to develop a synthetic method for obtaining asymmetrical organophosphate in the future. We are planning to expand on the knowledge gained here, either to start in the current directions (finding thiophosphate molecules that can be separated), to develop established chemistry (finding a way to prevent the development of tetraethyl diphosphate) or to move in different directions.

46 CHAPTER THREE

EXPERIMENTAL

3.1 Reagents

All the reactions were carried out under strictly anhydrous, air-free conditions

under nitrogen. All solvents were dried and distilled using a 5 column Inert Technologies

PureSolv MD5 solvent purification system. Slow additions were performed using a KDS

Legacy Nanoliter Dual Syringe Pump. 1H and 31P spectra were acquired on a BRUKER

1 300 MHz NMR in CDCl3. The H chemical shifts are given in parts per million (δ) with an

internal tetramethylsilane (TMS, δ 0.00 ppm) standard and the 31P chemical shifts were

recorded with an internal standard (using phosphoric acid that was inserted in a glass

capillary tube and placed in the NMR tube), or an external phosphoric acid standard

(phosphoric acid was standardized to δ 0.00 ppm). NMR data are reported in the following

format: a chemical shift (multiplicity (s = singlet, d= doublet, t = triplet, q = quartet),

integration, coupling constants [Hz]). All measurements were recorded at 25 °C unless

otherwise stated. Purification was typically performed using a Teledyne Combiflash®

purification system equipped with UV detection. All chemicals were synthesized in our

lab or purchased from Sigma, TCI America, AK Scientific, Acros, STREM, or Fischer.

Molecular masses were determined through GC/MS instrumentation with a Trace 1310

Gas Chromatography/ISQ 7000 Single Quadrupole Mass Spectrometer with a direct probe.

47 3.2 The Synthesis of Chiral Organophosphate from POCl3

Distillation of the phosphorus oxychloride, 1:

30 mL of phosphorus oxychloride was placed in a 100 mL round bottom flask that was equipped with a stir bar, a reflux condenser, and then a drying tube. The material was heated to reflux for 30 min to remove any residual hydrochloric acid. The reflux condenser and drying tube were removed, and the phosphorus oxychloride was distilled.

3.2.1 The Synthesis of 3,5-Dimethoxyphenyl (4-Methoxyphenyl) (4-Benzyl-2-

Oxazolidin-3-yl) Phosphonate, 4

3.2.1.1 Screening of bases and solvents in the synthesis of 3,5-dimethoxyphenyl (4-

methoxyphenyl) (4-benzyl-2-oxooxazolidin-3-yl) phosphonate, 4

Figure 38. The multi-step sequence for the synthesis of 3,5-dimethoxyphenyl (4- methoxyphenyl) (4-benzyl-2-oxazolidine-3-yl) phosphonate

Phosphorus oxychloride (0.440 mmol, 1 eq., 0.0675g) was added to a new dry 50

mL round bottom flask using 1 mL syringe and sealed with a rubber septum under nitrogen.

A (R)-4-Benzyl-2-oxazolidinone (0.0782g, 0.440 mmol) was placed in a 50 mL dry round

48 bottom flask, dissolved in 10 mL of dry THF and equipped with nitrogen. The reaction

flask was cooled to -78°C using dry ice and acetone in a Dewar before adding the base. 1

mL of the appropriate base solution at a concentration of 0.440 mmol/mL was added to the

flask of the (R)-4-Benzyl-2-oxazolidinone solution dropwise. The solution of the

oxazolidinone then was added to the flask containing phosphorus oxychloride dropwise in

a nitrogen environment and cooled to -78°C. The reaction was allowed to warm up to room

temperature overnight. The crude reaction was monitored by 31P NMR.This is the first

synthetic step of three.

Attempted Purification of 2: The solvent was removed using rotary evaporator, re-

dissolved in a minimal amount of dry CH2Cl2 then filtered through a filter using a 150 mL

medium fritted funnel to remove any precipitates, then the filtered solution was taken and

mixed in CH2Cl2 and water in the separatory funnel, the reaction has been extracted and lets it separated into two layers for 5 minutes. The resulting filtrate was concentrated again in a rotary evaporator to remove the solvent. Further, the crude reaction mixture was

dissolved in CH2Cl2 and purified by column chromatography using ethyl acetate/hexane

(3:7) using the Combiflash® purification system and the reaction was characterized by 31P

NMR. Using this method, 2 could not be isolated and thus was used in the next reaction step without purification.

The crude reaction mixture from above was taken to perform the second substitution step. p-methoxyphenol (0.440 mmol, 1 eq., 0.0546g) was placed in a 50 mL round bottom flask under nitrogen and dissolved in 5 mL THF. The appropriate base was then dissolved in 5 mL of dry THF in a 10 mL flask to give a concentration of 0.440 mmol/mL. The 50 mL round bottom flask was then cooled to -78 °C, and the 1 mL of the

49 base solution (0.440 mmol, 1 eq.) was then added to p-methoxyphenol. After stirring for

15 minutes, the solution of the phenoxide was then added to the crude reaction mixture

from step one. The reaction was stirred for 60 min. and allowed to warm up to room

temperature overnight. This is the second synthetic step out of three.

In the third substitution step, 3,5-dimethoxyphenol (0.0673g, 1 eq., 0.440 mmol)

was placed in a 50 mL round bottom flask under nitrogen, dissolved in 5 mL THF. The

appropriate base was then dissolved in 5 mL of dry THF in a 10 mL flask to a final

concentration of 0.440 mmol/mL. A 50 mL round bottom flask was then cooled to -78 °C, and the 1 mL of the base solution was then added to 3,5-dimethoxyphenol. After stirring

for 15 minutes, the solution of the 3,5-dimethoxyphenol was then added to the crude

reaction mixture from step two. The reaction was stirred for 60 min. and allowed to warm

up to room temperature overnight. The reaction was monitored by 31P NMR.

Attempted Purification of 4: The solvent was removed in rotary evaporator, re-

dissolved in a minimal amount of dry CH2Cl2 then filtered through a filter using a 150 mL

medium fritted funnel to remove any precipitates, then the filtered solution was taken

mixed in CH2Cl2 and water in the separatory funnel, the reaction has been extracted and

lets it separated into two layers for 5 minutes. The resulting filtrate was concentrated again

in rotary evaporator to remove the solvent. Further, a crude mixture was dissolved in

CH2Cl2 and purified by column chromatography using ethyl acetate/hexane (3:7) using

the Combiflash® purification system. Solvent was removed by rotary evaporation, placed

under high vacuum for 15 minutes, and characterized by 1HNMR (300 MHz, Chloroform-

d) δ 8.08 (s, 1H), 7.97 – 7.84 (m, 12H), 7.67 (s, 4H), 7.18 (d, J = 7.5 Hz, 3H), 6.40 (s,

1H), 6.25 (s, 1H), 4.37 (s, 1H), 4.12 (s, 2H), 3.86 – 3.77 (m, 2H), 3.70 (d, J = 10.0 Hz,

50 7H), 3.53 (s, 2H), 3.32 (s, 21H), 3.01 (d, J = 13.5 Hz, 2H), 2.85 (s, 1H), 0.07 (s, 2H).

31 PNMR (122 MHz, CDCl3) data is listed below. In the presence of proton sponge as a

base, the following peaks were observed: δ 4.95, 1.99, -3.48. BuLi as a base gave no peak

in the phosphorus NMR.

3.2.1.2 Screening of Lewis acids in the synthesis of 3,5-dimethoxyphenyl (4-

methoxyphenyl) (4-benzyl-2-oxazolidin-3-yl) phosphonate, 4

Figure 39. The use of Lewis acid metal catalyst to synthesis 3,5-dimethoxyphenyl (4- methoxyphenyl) (4-benzyl-2-oxazolidine-3-yl) phosphonate

The same standard procedure for the synthesis of product 4 was used with the applying of a Lewis metal catalyst. those metals have been applied to the crude product from the first substitution of the addition of chiral auxiliary. The crude product ((4-benzyl-

2-oxazolidin-3-yl)phosphonic dichloride) was placed into three different round bottom flasks, then the appropriate metal catalyst solution, Mg(OTf)2 (0.01418 g, 0.1eq., 0.440 mmol), TiO2 (0.00281 g, 0.1eq., 0.440 mmol) and AlCl3 (0.00587 g, 0.1eq., 0.440 mmol) was added dropwise and stirred for 60 min in room temperature. Each metal was added before the second substitution step, p-methoxyphenol (0.440 mmol, 1 eq., 0.0546g) as shown in Figure 39. Allow the reaction for an hour, then let it warm up to room temperature 51 overnight. After this, the third substitution was preformed by adding 3,5-dimethoxyphenol

(0.0673g, 1 eq., 0.440 mmol) to the crude product. 31P NMR was regulated for each step

and the purification of 4 followed the same non-catalyst reaction purification procedure.

Following the vacuum treatment of the solution. After vacuum removal of the solvent, the

basic reaction mixture yielded 31P NMR (122 MHz, CDCl3) of the following peaks by 31P

NMR (122 MHz, CDCl3) data is shown Mg(OTf)2 δ = -6.92; TiO2 δ = -7.06; AlCl3 δ = -

6.90.

3.2.2 The Synthesis of 4-Benzyl-2-Oxazolidin-3-yl Ethyl Methyl Phosphate, 6:

3.2.2.1 Screening of bases and solvents in the synthesis of 4-benzyl-2-oxazolidin-3-yl

ethyl methyl phosphate, 6:

Attempt one: starting with a chiral auxiliary followed by alkyl groups:

Figure 40. The synthesis of 4-benzyl-2-oxazolidin-3-yl ethyl methyl phosphate– attempt one

Following the standard procedure for the synthesis of 4, phosphorus oxychloride

(0.067g, 0.440 mmol) in 50 mL round bottom flask sealed with a rubber septum. The (R)-

4-Benzyl-2-oxazolidinone (0.0782g, 1eq., 0.440 mmol) in a 50 mL dry round bottom flask

52 and dissolved using 10 mL of dry DCM, purged with nitrogen and placed in dry ice and acetone in a Dewar and cooled to -78°C before adding the base. The Proton Sponge®

(0.0943g, 1eq., 0.440 mmol) in 5 mL of dry DCM was transferred dropwise to the flask containing (R)-4-Benzyl-2-oxazolidinone solution. The solution of the deprotonated oxazolidinone was added to phosphorus oxychloride in dropwise, nitrogen environment dry DCM, and cooled to -78 °C. the reaction stirs for 60 min. then was allowed to warm up to room temperature overnight. This is the first synthetic step out of three. The reaction was monitored by 31P NMR.

The crude reaction mixture from above was taken to perform the second substitution step. MeOH (0.440 mmol, 1 eq., 0.0546g) was placed in a 25 mL round bottom flask under nitrogen and dissolved in 11.25 mL THF and then cooled to -78 °C. Proton

Sponge® was then dissolved in 5 mL of dry THF in a 25 mL flask to give a concentration of 0.440 mmol/mL. 1 mL of the base solution (0.440 mmol, 1 eq.) was then added to the methanol solution dropwise. After stirring for 15 min., the solution of the methoxide was then added to the crude reaction mixture from step one. The reaction was stirred for 60 min. at low temperature and allowed to warm up to room temperature overnight. This is the second synthetic step out of three. The reaction was monitored by 31P NMR.

The crude reaction mixture from above was taken to perform the third substitution step. Ethanol and the appropriate base were both diluted and mixed at -78 °C to a final concentration of 0.440 mmol/mL of ethoxide. Then, 1 mL of this solution was added dropwise to the crude product of the first step at -78 °C, stirred for 60 minutes, and left to warm up to room temperature overnight. The reaction was monitored by 31P NMR.

53 Attempted Purification of 6: To purify the reaction, the solvent was removed in

rotary evaporator, re-dissolved in a minimal amount of dry CH2Cl2 then filtered through

celite using a 150 mL medium fritted funnel to remove the strong base. Then, the filtered

solution was taken mixed in CH2Cl2 and water in the separatory funnel, then extracted with

CH2Cl2 with aqueous NaOH; were easily separated into two layers for 5 minutes. The

resulting from the filtrate was concentrated again in rotary evaporator and distilled to

remove any precipitates. Further, a crude solution prepared using CH2Cl2 and purified by column chromatography using a Combiflash® purification system with ethyl acetate/hexane (3:7), followed with the removal of the solvent in rotary evaporator and characterized in 1HNMR (300 MHz, CDCl3) δ 7.32 (s, 1H), 4.42 (s, 1H), 3.83 (s, 5H), 3.09

31 (s, 2H), 1.42 (s, 1H). PNMR (122 MHz, CDCl3), the BuLi δ 2.40, 0.03, while the

MeMgCl -4.97.

Attempt two: starting with the alkyl groups followed by a chiral auxiliary:

Figure 41. The synthesis of 4-benzyl-2-oxazolidin-3-yl ethyl methyl phosphate – attempt two

Phosphorus oxychloride (0.067g, 0.440 mmol) was added to a 50 mL round bottom

flask sealed with a rubber septum and purged with nitrogen, then placed in dry ice and

54 acetone in a Dewar and cooled to -78 °C. In a separate flask, a solution of Proton Sponge®

and methanol was prepared, containing 0.440 mmol/mL of each, and 1 mL of that solution

was transferred dropwise to the round bottom flask containing phosphorus oxychloride.

The reaction was stirred for 60 min and left to warm up to room temperature overnight.

This is the first step of three.

The crude reaction mixture from above was taken to perform the second substitution step. Ethanol and the appropriate base were both diluted and mixed at -78 °C

to a final concentration of 0.440 mmol/mL of ethoxide. Then, 1 mL of this solution was

added dropwise to the crude product of the first step at -78 °C, stirred for 60 minutes, and

left to warm up to room temperature overnight. The reaction was monitored by 31P NMR.

The (R)-4-Benzyl-2-oxazolidinone (0.0782g, 1eq., 0.440 mmol) and the

appropriate base were both diluted and mixed at -78 °C to a final concentration of 0.440

mmol/mL. Then, 1 mL of this solution was added dropwise to the crude products from the second step in dropwise, at -78 °C, stirs for 60 min. and left to warm up to room temperature overnight. The reaction was monitored by 31P NMR. This is the third synthetic step out of

three.

Attempted purification of 6: The solvent was removed in rotary evaporator, re-

dissolved in a minimal amount of dry CH2Cl2 then filtered through celite using a 150 mL

medium fritted funnel to remove the strong base. Then, the filtered solution was taken

mixed in CH2Cl2 and water in the separatory funnel, then extracted with CH2Cl2 with

aqueous NaOH; were easily separated into two layers for 5 minuets, the resulting from the

filtrate was concentrated again in rotary evaporator and distilled to remove any precipitates.

Further, a crude solution prepared using CH2Cl2 and purified by column chromatography

55 Combiflash® using ethyl acetate/hexane (3:7), followed with rotary evaporator and fully

characterized in 1H NMR (300 MHz, Chloroform-d) δ 7.52 – 7.36 (m, 6H), 7.35 – 7.29 (m,

3H), 5.53 (s, 1H), 4.59 (t, J = 7.8 Hz, 2H), 4.30 (d, J = 5.4 Hz, 1H), 4.23 (dd, J = 13.2, 6.7

Hz, 2H), 3.00 (d, J = 6.6 Hz, 3H), 0.20 (d, J = 2.5 Hz, 4H).

3.2.2.2 Screening of Lewis acids in the synthesis of 4-benzyl-2-oxazolidin-3-yl ethyl

methyl phosphate, 6:

In the lab, a chemical reaction that involves the presence of the metal using the same standard procedure for synthesizing 6, was tested using the phosphorus oxychloride

as starting material and methanol represent the first nucleophile substituting with one of

the chlorines that attached to the phosphorus center

Figure 42. The synthesis of 4-benzyl-2-oxazolidin-3-yl ethyl methyl phosphate, using Lewis acid metal catalyst

The same standard procedure for the synthesis of product 6 was used with the

applying of a Lewis metal catalyst. those metals have been applied to the crude product

from the first substitution of the addition of chiral auxiliary.

56 The crude product ((4-benzyl-2-oxazolidin-3-yl)phosphonic dichloride) was placed in a round bottom flask, then the appropriate metal catalyst solution Mg(OTf)2 (0.01418 g, 0.1eq., 0.440 mmol), TiO2 (0.00281 g, 0.1eq., 0.440 mmol) and AlCl3 (0.00587 g,

0.1eq., 0.440 mmol) was added dropwise and stirred for 60 min in room temperature. Each metal was added before the second substitution step.The Methanol solution was the second step to replace the second Cl with a strong base. Methanol and the required base were all distilled and mixed at-78 ° C at a final concentration of 0,440 mmol / mL of methoxide.

Then, 1 mL of this solution was added dropwise to the crude product of the first step at -

78 °C, stirred for 60 minutes, and left to warm up to room temperature overnight. The reaction was monitored by 31P NMR. This is the second step of three.

Same procedure performed for the second addition of the metal to the third step of the reaction, by mixing the crude product of the second substitution with a mixed solution of ethanol and the appropriate base were both diluted and mixed at -78 °C to a final concentration of 0.440 mmol/mL of ethoxide. Then, 1 mL of this solution was added dropwise to the crude product of the first step at -78 °C, stirred for 60 minutes, and left to warm up to room temperature overnight. The reaction was monitored by 31P NMR. This is the third step of the three.

Attempted Purification of 6: The solvent was removed in rotary evaporator, re- dissolved in a minimal amount of dry CH2Cl2 then filtered through celite using a 150 mL medium fritted funnel to remove the strong base. Then, the filtered solution was taken mixed in CH2Cl2 and water in the separatory funnel, then extracted with CH2Cl2 with aqueous NaOH; were easily separated into two layers for 5 minutes the resulting from the filtrate was concentrated again in rotary evaporator and distilled to remove any precipitates.

57 Further, a crude solution prepared using CH2Cl2 to dissolve it and purified by column chromatography Combiflash® using ethyl acetate/hexane (3:7), followed with rotary

13 3 evaporator and fully characterized in P NMR (122 MHz, CDCl3) C2F6MgO6S2 δ -1.81,

-5.79, TiO2 δ 1.80, -6.54, AlCl3 δ 1.30, -6.38.

3.2.3 The Synthesis Of 4-Benzyl-2-Oxazolidin-3-yl Decyl Methyl Phosphate, 10:

Figure 43. The synthesis of 4-benzyl-2-oxazolidin-3-yl decyl methyl phosphate

The reaction followed the same standard procedure was performed in synthesizing

6, phosphorus oxychloride (0.067g, 0.440 mmol) in 50 mL round bottom flask sealed with a rubber septum. The (R)-4-Benzyl-2-oxazolidinone (0.0782g, 1eq., 0.440 mmol) and the appropriate base were both diluted and mixed at -78 °C to a final concentration of 0.440 mmol/mL. Then, 1 mL of this solution was added dropwise to the phosphorus oxychloride in a dropwise, at -78 °C, stirs for 60 min. and left to warm up to room temperature overnight. The reaction was monitored by 31P NMR. This is the first synthetic step out of three.

Octanol (0.0692 mL, 1 eq., 0.440 mmol) and the appropriate base were both diluted and mixed at -78 °C to a final concentration of 0.440 mmol/mL. Then, 1 mL of this solution was added dropwise to the crude product from the first step, in a dropwise, at -78 °C, stirs

58 for 60 min. and left to warm up to room temperature overnight. The reaction was monitored by 31P NMR. This is the second synthetic step out of three.

The methanol and the appropriate base were both diluted and mixed at -78 °C to a final concentration of 0.440 mmol/mL of methoxide. Then, 1 mL of this solution was added dropwise to the crude product of the first step at -78 °C, stirred for 60 minutes, and left to warm up to room temperature overnight. The reaction was monitored by 31P NMR. This is the third step of the three.

Attempted Purification of 10: The solvent was removed in rotary evaporator, re- dissolved in a minimal amount of dry CH2Cl2 then filtered through celite using a 150 mL medium fritted funnel to remove the strong base. Then, the filtered solution was taken mixed in CH2Cl2 and water in the separatory funnel, then extracted with CH2Cl2 with aqueous NaOH; were easily separated into two layers for 5 minutes the resulting from the filtrate was concentrated again in rotary evaporator and distilled to remove any precipitates.

Further, a crude solution prepared CH2Cl2 to dissolve it and purified by column chromatography Combiflash® using ethyl acetate/hexane (3:7), followed with rotary evaporator and fully characterized in 1H NMR (300 MHz, Chloroform-d) δ 7.27 (d, J =

11.0 Hz, 2H), 4.41 (s, 1H), 4.15 (s, 1H), 3.90 (s, 6H), 1.68 (s, 1H), 1.28 (d, J = 10.8 Hz,

4H), 0.88 (t, J = 6.8 Hz, 1H). No peak for 13P NMR

59 3.3 The Synthesis of P-Chiral Organophosphates From Alkyl Phosphorus

There were a different set of starting material used to start reactions with POCl3.

The phenyl phosphorodichlordate was reacted with the alkyl group (methanol) and chiral auxiliary in the presence of a strong base.

3.3.1 The Synthesis of 4-Benzyl-2-Oxazolidin-3-yl Methyl Phenyl Phosphate, 13:

Attempt one: (R)-4-Benzyl-2-oxazolidinone and Methanol

Figure 44. The synthesis of 4-benzyl-2-oxazolidin-3-yl methyl phenyl phosphate - attempt one

The chemical reaction took a place in a 100 mL round bottom flask where a starting

material (the phenyl phosphorochlordate) was distilled before the reaction. Following the

standard procedure for the synthesis of compound 4. The phenyl phosphorodichlordate

(0.0928g, 1 eq., 0.440 mmol) was placed in 50 mL round bottom flask sealed with rubber

septum while the (R)-4-Benzyl-2-oxazolidinone (0.0782g, 1eq., 0.440 mmol) dissolved in

solvent, and the appropriate base was diluted to the final concentration of 0.440 mmol,

using the solvent that used for the reaction, and mixed at -78 °C. Then, 1 mL of the base

mixed with (R)-4-Benzyl-2-oxazolidinone solution was mixed with the base then added

dropwise to the phosphorus oxychloride, at -78 °C, stirs for 60 min and left to warm up to

60 room temperature overnight. The reaction was monitored by 31P NMR. This is the first

synthetic step out of two.

The crude product from the first step was mixed with methanol solution that was

diluted to a final concentration of 0.440 mmol/mL. The appropriate base was diluted as

well (same concetration of 0.440 mmol/mL) and both were mixed at -78 °C to give

methoxide compound. Then, 1 mL of the mixed solution was added dropwise to the crude

product of the first step at -78 °C, stirred for 60 minutes, and left to warm up to room

temperature overnight. The reaction was monitored by 31P NMR. This is the second step of two.

Attempted purification of 13: The solvent was removed by rotary evaporation and

31 characterized before any isolation by P NMR (122 MHz, CDCl3) δ -7.25, -8.57, -10.49,

-15.37. The crude product was re-dissolved in a minimal amount of dry CH2Cl2, and

filtered through celite using a 150 mL medium fritted funnel to remove the strong base.

Then the filtrate was mixed in CH2Cl2 and water in the separatory funnel, extracted using

CH2Cl2 in a separatory funnel then an aqueous NaOH added; the solution can be simply divided conveniently into two layers for 5 minutes., then the resulting filtrate was concentrated again in rotary evaporator and distilled to remove any precipitates. Further, a crude solution prepared using CH2Cl2 to dissolve it and purified by column

chromatography using ethyl acetate/hexane (3:7), followed with rotary evaporator and

1 fully characterized in H NMR (300 MHz, CDCl3) δ 8.11, 7.99, 7.31, 7.28, 7.25, 7.09, 5.84,

5.52, 5.31, 5.25, 4.27, 4.17, 3.97, 3.79, 3.69, 3.47, 3.10, 3.07, 2.82, 2.20, 1.86, 1.35, 1.27,

31 0.97, 0.94, 0.92, 0.87, 0.09. P NMR (122 MHz, CDCl3) δ -7.25, -8.57, -10.49, -15.37.

61 Attempt two: Methanol and (R)-4-Benzyl-2-oxazolidinone

Following attempt one, the procedure to synthesis 13 used (R)-4-Benzyl-2- oxazolidinone as a first substitution, followed by methanol as a second substitution.

Figure 45. The synthesis of 4-benzyl-2-oxazolidin-3-yl methyl phenyl phosphate - attempt two

The phenyl phosphorodichlordate (0.0928g, 1 eq., 0.440 mmol) was placed in a 50 mL round bottom flask sealed with rubber septum, was mixed with a methanol solution that was diluted to final concetration of 0.440 mmol/mL, and the appropriate base (BuLi or

MeMgCl at a concentration of 0.440 mmol /mL. Both solutions were mixed at-78 ° C to create a methoxide compound. Then 1 mL of this solution was introduced in dropwise to the first step crude product at-78 ° C, stirred for 60 minutes, and left to warm up to room temperature overnight. The response was supervised by 31P NMR. It's the first synthetic phase out of two. A crude product from the first step was mixed with the (R)-4-Benzyl-2- oxazolidinone (0.0782g, 1eq., 0.440 mmol) and the appropriate base was diluated to a final concetration of 0.440 mmol/mL, then both were mixed at -78 °C. Then, 1 mL of this solution was added dropwise to the phosphorus oxychloride in a dropwise, at -78 °C, stirred

62 for 60 min. and left to warm up to room temperature overnight. The reaction was monitored

by 31P NMR. This is the second step of two.

Attempted purification of 13: The solvent was removed in rotary evaporator, re-

dissolved in a minimal amount of dry CH2Cl2, then filtered through celite using a 150 mL medium fritted funnel to remove the strong base. The filtered solution was taken and mixed

with CH2Cl2 and water in the separatory funnel, extracted with CH2Cl2 and added an

aqueous NaOH; let it separated for for 5 minutes into two layers, giving an easily

separation, then the resulting solution was filtared followed with a concentrated in rotary

evaporator and distilled to remove any precipitates. Further, a crude solution prepared

CH2Cl2 to dissolve it and purified by column chromatography Combiflash® using ethyl

acetate/hexane (3:7), followed with rotary evaporator and fully characterized in 1H NMR

(300 MHz, CDCl3) δ 7.94, 7.32, 7.29 (d, J = 16.8 Hz, 14H), 7.20 (s, 7H), 7.05 (s, 2H), 5.42,

4.34 (s, 1H), 4.09 (s, 2H), 3.83 (s, 24H), 3.76 – 3.66 (m, 4H), 3.47 (s, 2H), 3.33,3.08 (s,

31 1H), 2.76 (s, 1H), 2.57, 2.25, 1.82, 1.26, 0.08. P NMR (122 MHz, CDCl3) δ -7.32, and -

4.29

63 3.3.2 The Synthesis of Benzyl Ethyl Methyl Phosphate, 16:

The starting material is the methyl phosphorodichlordate was reacted with the alkyl

group, ethanol, and benzyl alcohol in the presence of a strong base.

Figure 46. The synthesis of benzyl ethyl methyl phosphate The methyl phosphorodichlordate (0.440 mL, 1 eq., 0.440 mmol) was placed in a

50 mL round bottom flask sealed with rubber septum, a mixture of 1 mL of diluted ethanol to a final concentration of 0.440 mmol/mL of ethoxide and the appropriate base (diluted to

a final concentration of 0.440 mmol/mL) at -78 °C. Then, 1 mL of this solution was added dropwise to the The methyl phosphorodichlordate at -78 °C, stirred for 60 minutes, and left to warm up to room temperature overnight. The reaction was monitored by 31P NMR. This

is the first step of two.

A crude product from the first step was mixed with a mixture of benzyl alcohol

(0.490 mL, 1 eq., 0.440 mmol) and the appropriate base was diluted (to a final

concentration of 0.440 mmol/mL) and mixed at -78 °C. Then, 1 mL of this solution was

added dropwise to the crude product of the first step at -78 °C, stirred for 60 minutes, and

left to warm up to room temperature overnight. The reaction was monitored by 31P NMR.

This is the second step of two.

Attempted purification of 16: The solvent was removed in rotary evaporator, re-

dissolved in a minimal amount of dry CH2Cl2, then filtered through celite using a 150 mL

64 medium fritted funnel to remove the strong base. Then, the filtered solution was taken

mixed in CH2Cl2 and water in the separatory funnel, extracted in CH2Cl2 with aqueous

NaOH; let it set for 5 minutes, resulting an easily separated into two layers, then followed by filtration, and the resulting from the filtrate was concentrated again in rotary evaporator and distilled to remove any precipitates. Further, a crude solution prepared using CH2Cl2

to dissolve it and purified by column chromatography® using ethyl acetate/hexane (3:7),

followed with rotary evaporator and fully characterized in 1H NMR (300 MHz,

Chloroform-d) δ 8.69 – 8.59 (m, 3H), 8.31 (q, J = 7.7 Hz, 2H), 7.92 (d, J = 7.3 Hz, 2H),

7.81 (q, J = 7.2 Hz, 3H), 7.25 – 6.99 (m, 11H), 6.62 (d, J = 7.2 Hz, 2H), 4.55 (d, J = 7.5

Hz, 2H), 4.19 (dq, J = 11.4, 6.6, 6.0 Hz, 1H), 3.52 (t, J = 6.5 Hz, 2H), 3.00 (d, J = 7.4 Hz,

31 5H), 1.65 (d, J = 6.6 Hz, 2H), 1.18 (dt, J = 14.4, 6.8 Hz, 3H). P NMR (122 MHz, CDCl3)

δ 18.76, 9.80.

65 3.4 Synthesis Of P-Chiral Organophosphates In Presence of Trialkyl Phosphorus and

Tf2O/Pyridine

3.4.1 The Synthesis of 4-Benzyl-2-Oxazolidin-3-yl Ethyl Phenyl Phosphate, 19:

Figure 47. The synthesis of 4-benzyl-2-oxazolidin-3-yl ethyl phenyl phosphate, forming phosphoryl pyridin-1-ium intermediate

Mixed solution of Tf2O (0.846 g, 1.5 eq., 0.600 mmol) and pyridine (0.322 mg, 2.0 eq., 0.800 mmol) in 2 mL DCM. It then reacted with triethyl phosphates (0.364 g, 1 eq.,

0.400 mmol) dissolved using 10 mL DCM in a 50 mL round bottom flask and let it react for 10 minutes at room temperature (Step A). a phenol (0.352 mL, 2.0 eq., 0.800 mmol) placed in 25 mL round bottom with DCM, then reacted with The solution of step A while it stir in room temperature for 30 minutes (Step B).

The crude product from the first step reacted with the mixed solution of Tf2O

(0.846g, 1.5 eq., 0.600 mmol,) and pyridine (0.322 mL, 2.0 eq., 0.800 mmol,) in 2 mL

DCM. The mixed solution was added in dropwise to the crude product and stir in room temperature for 10 minutes (Step A). Then the solution of the (R)-4-Benzyl-2- oxazolidinone (0.142g, 2.0 eq., 0.800 mmol) in 5 mL DCM added to the mixture of the crude product (step 1, A) and stirred in the room temperature for 30 minutes (Step B).

66 Attempted purification of 19: The resulting mixture was concentrated by

evaporating the solvent using reduced pressure to give the crude product. Further, a crude

solution prepared using CH2Cl2 to dissolve it and purified by column chromatography

Combiflash® using ethyl acetate/hexane (3:7), followed with Vacuum to evaporate the

solvent using reduced pressured to give a product that can fully characterized in 1H NMR

(300 MHz, Chloroform-d) δ 8.64 (d, J = 6.0 Hz, 1H), 7.84 (dt, J = 17.4, 6.6 Hz, 1H), 7.33

– 7.05 (m, 3H), 6.90 – 6.72 (m, 5H), 4.49 (q, J = 7.3 Hz, 1H), 4.27 – 3.98 (m, 4H), 1.55 –

31 1.32 (m, 2H), 1.28 (ddd, J = 9.9, 6.7, 2.1 Hz, 5H). P NMR (122 MHz, CDCl3) δ -0.81, -

6.60, -13.78.

3.4.2 The Synthesis of Benzyl Ethyl Phenyl Phosphate, 24:

Figure 48. The reaction of synthesis benzyl ethyl phenyl phosphate, step a and step b in first step substitution

Trialkyl phosphates (0.364g, 1 eq., 0.400 mmol) dissolved using 10 mL DCM,

placed in 50 mL round bottom flask, reacted with a mix solution of Tf2O (0.846g, 1.5 eq.,

0.600 mmol,) and pyridine (0.322 mL, 2.0 eq., 0.800 mmol,) in 2 mL DCM. Then the

mixed solution of Tf2O and pyridine added to the trialkyl phosphate in dropwise, let it stir

and react for 10 minutes at room temperature (Step A).Followed with the addition of benzyl

alcohol (0.0415 mL, 2.0 eq., 0.400 mmol) placed 25 mL round bottom flask in DCM.

67 Benzyl alcohol solution added to step A and let stir in room temperature for 30 minutes

(Step B).

Figure 49. The reaction of synthesis benzyl ethyl phenyl phosphate, step a and step b all two-steps substitution

The crude product from the first step reacted with the mixed solution of Tf2O

(0.846g, 1.5 eq., 0.600 mmol,) and pyridine (0.322 mL, 2.0 eq., 0.800 mmol,) in 2 mL

DCM. the mixed solution of Tf2O and pyridine then added in dropwise to the crude product

and stir in room temperature for 10 minutes (Step A). Followed with the addition of Phenol

(0.352 mL, 2.0 eq., 0.800 mmol) placed in 25 mL round bottom and DCM. The Phenol solution and step A mixed stir in room temperature for 30 minutes (Step B).

Attempted purification of 24: The resultant mixture was concentrated by evaporating

solvent using vacuum to give the crude product. Further, a crude solution prepared using

CH2Cl2 to dissolve it and purified by column chromatography Combiflash® using ethyl

acetate/hexane (3:7), followed with rotary evaporator and fully characterized in 1H NMR

(300 MHz, Chloroform-d) δ 8.74 – 8.32 (m, 0H), 8.01 (d, J = 6.8 Hz, 0H), 7.40 – 7.10 (m,

0H), 6.99 – 6.48 (m, 0H), 4.02 (p, J = 7.3 Hz, 1H), 1.24 (t, J = 7.1 Hz, 2H). 31P NMR (122

MHz, CDCl3) δ -1.66, -2.78, -13.38, -13.98, -14.09, -26.12.

68 3.5 Synthesis Of P-Chiral Thiophosphate

3.5.1 The Synthesis of Ethyl Methyl Phenyl Phosphorothioate, 23:

Attempt one: Ethyl methyl phenyl phosphorothioate, 23 using a weak base

Figure 50. The synthetic sequence for ethyl methyl phenyl phosphorothioate - attempt one

Phosphorous thiochloride (0.0677g, 1 eq., 0.400 mmol) placed in 50 mL round

bottom flask in THF, cooled in dry ice to -78 °C. A mixture of phenol (0.0346g, 1 eq.,

0.400 mmol) and 1 mL of pyridine solution (0.322 mL, 10 mL THF) stirs for 10 minutes at room temperature, then added to the phosphorous thiochloride in dropwise, stirred at -

78 °C for 1 hour. The reaction was set overnight to let it warm up from - 78 °C to room

temperature. The reaction was monitored by 31P NMR. This is the first step of three

A mixture of 1 mL of diluted ethanol to a concetration of 0.400 mmol/mL and the appropriate weak base (pyridine) were mixed at room temperature. Then, the mixed solution was mixed with a crude product of the phenyl dichlorothiophosphate. the reaction stirs at -78 °C for 1 hour. Then let it set to warm up to room temperature overnight., The reaction was monitored by 31P NMR. This is the second step of three

The third step is a mixture of diluated methanol to a final concentration of 0.440

mmol/mL with an appropriate weak base (pyridine) at room temperature. Then, the mixed

solution was mixed with a crude product of the second reaction. the reaction stirs at -78

69 °C, for 1 hour. The final reaction was set to warm up to room temperature overnight. Then,

it was characterized by 31P NMR. This is the third step of three

Attempted purification of 23: The solvent was removed in rotary evaporator, re-

dissolved in a minimal amount of dry CH2Cl2, washed with CH2Cl2 and water in the separatory funnel, then extracted with CH2Cl2 with aqueous NaOH; let it set for 5 minutes,

an easily separated into two layers. Then, it followed with filtration process taking the

resulting from the filtrate and concentrated again in rotary evaporator and distilled to

remove any precipitates. Further, a crude solution prepared using CH2Cl2 to dissolve it and

purified by column chromatography Combiflash® using ethyl acetate/hexane (3:7),

1 followed with rotary evaporator and fully characterized in H NMR (300 MHz, CDCl3) δ

4.12, δ 3.55 – 3.45 (m, 1H), 3.52, 3.51, 3.50, 3.49, 3.48, 3.43, 3.40, 3.17, ) 1.67 – 1.55 (m,

31 1H). 1.67, 1.64, 1.63, 1.62, 1.61, 1.60, 1.58, 0.99, 0.97, 0.95. P NMR (122 MHz, CDCl3)

δ 65.32, 62.74, -4.13.

Attempt two: Ethyl methyl phenyl phosphorothioate, 23 using organocatalytic

Figure 51. The reaction of synthesis ethyl methyl phenyl phosphorothioate - attempt two

The phenyl dichlorothiophosphate (0.1g, 1 eq., 0.440 mmol) placed in 50 mL round

bottom flask in THF, cooled in dry ice to -78 °C. A mixture of phenol (0.0346g, 1 eq.,

0.400 mmol) and 1 mL of pyridine solution (0.322 mL, 10 mL THF) stirs for 10 minutes

70 at room temperature. The HyperBTM (0.0123g, 1 eq., 0.440 mmol) added to the phenyl

dichlorothiophosphate, while it stirs the mixture solution of ethanol and pyridine added in

dropwise. It was cooled to -78 °C, stir for 1 hour then let set in the lab hood to warm up to room temperature overnight. The reaction was monitored by 31P NMR. This is the first

step of two

The crude product from the first step reaction reacted with a mixture of methanol

and the appropriate weak base (pyridine) were both diluted and mixed at room temperature

for 10 minutes to a final concentration of 0.440 mmol/mL of methoxide. Then, 1 mL of

this solution was added dropwise to the crude product of the first step at -78 °C, stirred for

60 minutes, and left to warm up to room temperature overnight. The reaction was

monitored by 31P NMR. This is the first synthetic step out of two.

The solvent was removed in rotary evaporator, re-dissolved in a minimal amount of dry CH2Cl2 then washed with CH2Cl2 and water in the separatory funnel, then extracted using CH2Cl2 with aqueous NaOH; let it set for 5 minutes, an easily separated into two

layers. Then, it followed with filtration process taking the resulting from the filtrate and

concentrated again in rotary evaporator and distilled to remove any precipitates.

Further, a crude solution prepared using CH2Cl2 to dissolve it and purified by

column chromatography Combiflash® using ethyl acetate/hexane (3:7), followed with

vacuo and fully characterized in 1H NMR (300 MHz, Chloroform-d) δ 8.00 (s, 1H), 7.42

(d, J = 7.5 Hz, 2H), 7.39 – 7.27 (m, 8H), 7.26 (s, 3H), 4.43 (th, J = 10.1, 3.6, 3.0 Hz, 3H),

3.82 – 3.68 (m, 23H), 1.92 – 1.80 (m, 21H), 1.49 (t, J = 7.0 Hz, 3H), 1.37 (t, J = 7.0 Hz,

31 2H), 1.25 (q, J = 6.2, 5.5 Hz, 4H). P NMR (122 MHz, CDCl3) δ 65.82, 63.73, 60.11.

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80 APPENDIX A

31P NMR Distilled Phosphorus Oxychloride

81 APPENDIX B 31P NMR result from reaction 1 from table 1

82 APPENDIX C

31P NMR result from reaction 2 from table 1

83 APPENDIX D 31P NMR result from reaction 1e in tabl 2 (in THF)

84 APPENDIX E 31P NMR result from reaction 3e in tabl 2 (in DCM)

85 APPENDIX F 31P NMR result from reaction 4e in tabl 2 (Proton Sponge®)

86 APPENDIX G

31 P NMR result from reaction 1 in table 3 using Mg(TfO)2

87 APPENDIX H

31 P NMR result from reaction 2 in table 3 using TiO2

88 APPENDIX I

31 P NMR result from reaction 3e in tabl 3 using AlCl3

89 APPENDIX J

31P NMR result from reaction 1 in table 4 (BuLi)

90 APPENDIX K 31P NMR result from reaction 2e in tabl 4 (MeMgCl)

91 APPENDIX L

31 P NMR result from reaction 1e ta bl 5 (left), Mg(TfO)2

92 APPENDIX M

31 P NMR result from reaction 2 in table 5 (middle), TiO2

93 APPENDIX N

31 P NMR result from reaction 3e in tabl 5 (right), AlCl3

94 APPENDIX O

31P NMR Phenyl dichlorophosphate

95 APPENDIX P

31P NMR result from reaction 1 table 6 in BuLi

96 APPENDIX Q

31P NMR result from reaction 2 table 6 in MeMgCl

97 APPENDIX R

31P NMR Triethyl phosphate

98 APPENDIX S

31P NMR result of the benzyl ethyl phenyl phosphonate

99 APPENDIX T

31P NMR Phenyl phosphorodichloridothioate

100 APPENDIX U

31P NMR result of the ethyl methyl phenyl phosphorothioate in HyperBTM

101 APPENDIX V

1H NMR result of the reaction 1 table 2

102 APPENDIX W

1H NMR result of reaction 1 table 4

103 APPENDIX X

1H NMR result of reaction 2 table 4

104 APPENDIX Y

1H NMR result of reaction 1 from table 6

105 APPENDIX Z

1H NMR result of the product 26

106