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Dissertation FINAL Post-Revisions ALL–CARBON ENE–TYPE CYCLIZATIONS FROM CYCLOHEXADIENE- TRICARBONYLIRON DERIVATIVES by KEITH B. BEACH Submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Thesis Advisor ANTHONY J. PEARSON, PH.D. Department of Chemistry CASE WESTERN RESERVE UNIVERSITY August 2016 CASE WESTERN RESERVE UNIVERSITY SCHOOL OF GRADUATE STUDIES We hereby approve the thesis/dissertation of Keith B. Beach candidate for the degree of Doctor of Philosophy. Committee Chair Robert G. Salomon, Ph.D. Committee Members Gregory P. Tochtrop, Ph.D. Rajesh Viswanathan, Ph.D. Yanming Wang, Ph.D. Date of Defense 02 May 2016 *We also certify that written approval has been obtained for any proprietary material contained therein. For my Grandfather, my Father and Clara Cree TABLE OF CONTENTS Table of Contents iv List of Equations vii List of Schemes viii List of Figures ix List of Tables xi Acknowledgements xii List of Abbreviations xiv Abstract xv Chapter 1. General Introduction: Diene–Tricarbonyliron Complexes 1 1.1 General Properties and Applications 2 1.1.1 Scope of Diene-Tricarbonyliron Complexes 3 1.1.1.1 Iron Carbonyl Reagents Used for Complexation 3 1.1.1.2 Preparation of Diene-Tricarbonyliron Complexes 5 1.1.1.3 Liberation of Diene Ligands from Iron Complexes 10 1.1.2 General Applications of Diene-Tricarbonyliron Complexes 12 1.1.2.1 Fe(CO)3 Moiety used as a Protecting Group 12 1.1.2.2 Fe(CO)3 Moiety used as a Stabilizing Group 15 1.1.2.3 Fe(CO)3 Moiety used as a Stereodirecting Group 17 1.2 Application Towards Stereogenic Quaternary-Carbon Formation 19 1.2.1 From Dienyl-Fe(CO)3 Substrates 20 1.2.1.1 Preparation 20 1.2.1.2 General Reactivity/Selectivity towards Nucleophilic Additions 21 1.2.1.3 Application: Synthesis of Trichodermol and Derivatives 23 1.2.1.4 Limitations of using Dienyl-Fe(CO)3 Complexes in Trichodermol 24 Analogue Synthesis 1.2.2 [6+2] Ene-Type Cyclizations 25 1.2.2.1 Progression towards Cyclizations from Diene-Fe(CO)3 Substrates 25 1.2.2.2 Scope of Ene-Type Cyclizations 28 1.2.2.2.1 Amide Derivatives 28 1.2.2.2.2 Ester and Thioester Derivatives 33 1.2.2.2.3 Stereoelectronic Considerations 35 – !iv – 1.2.2.3 Transition to All-Carbon Cyclizations 37 1.3 References 40 Chapter 2. All-Carbon [6+2] Ene-Type Cyclizations of (Cyclohexadiene)-Tricarbonyl 47 Iron Derivatives 2.1 Background: All-Carbon Spirocyclizations 48 2.1.1 Acyclic Substrates 48 2.1.2 Cyclic Substrates 50 2.2 Project Aim: Cyclizations from α-Alcohol Derivatives 51 2.3 Single Cyclizations 54 2.3.1 Unsubstituted (Cyclohexa-1,3-diene)-Fe(CO)3 Substrates 54 2.3.2 3-Methoxy Substituted (Cyclohexa-1,3-diene)-Fe(CO)3 Substrates 60 2.4 Attempts at Tandem Double Cyclizations from Alcohol Derivatives 65 2.4.1 Mono-Cyclization Attempts with Di-Substituted Pendant Olefin 65 2.4.2 Tandem Double Cyclization Attempts 69 2.5 Conclusions 71 2.6 Experimental Section 72 2.7 References 89 Chapter 3. Generality of Stereocontrol During Grignard Additions to 92 (Cyclohexa-1,3-dienylcarbaldehyde)-Tricarbonyl Iron 3.1 Introduction: Alkyl Additions to Carbonyl-Functionalized Diene-Fe(CO)3 Derivatives 93 3.1.1 Explanation of Stereochemical-Descriptor Terminology 93 3.1.2 Alkyl Additions to Acyclic Complexes 94 3.1.2.1 Experimental Observations of Alkylations of Complexed 94 Dienylcarbaldehydes & Dienones 3.1.2.2 Accepted Model for Alkyl Additions to Dienylcarbaldehyde-Fe(CO)3 97 Complexes 3.1.3 Additions to Cyclic Derivatives 98 3.2 Grignard Additions to Cyclohexa-1,3-dienylcarbaldehyde Complexes 99 3.2.1 Observed Selectivities en route to Spirocyclic Complexes 99 3.2.1.1 Additions to Dienylcarbaldehyde-Fe(CO)3 Derivatives 100 3.2.1.2 Determination of Configuration at α-Carbon via NOE Studies 103 3.2.1.3 Comparison of Results to Acyclic Series 105 3.2.2 Observed Selectivities from Generic Grignard Additions 106 – !v – 3.3 Conclusions 109 3.4 Experimental Section 110 3.5 References 113 Chapter 4. Future Works and Concluding Remarks 116 Appendix 120 Bibliography 142 – !vi – LIST OF EQUATIONS 1.1: Isomerization of 1,4-dienes to form conjugated diene-Fe(CO)3 complexes 5 1.2: Stereoselective iron complexation 9 1.3: Formation of (cyclobutadiene)-Fe(CO)3 15 1.4: Complexation of reactive o-quinodimethane 15 1.5: Addition of tetrafluoroethane to (cyclohexa-1,3-diene)-Fe(CO)3 28 1.6: Ene-type spirocyclizations of amide derivatives 28 1.7: Thermal stability of (methyl 3-methoxycyclohexa-1,3-dienecarboxylate)-Fe(CO)3 31 1.8: Formation of enone from mixture of spirocycle complexes 31 1.9: Double cyclization of an amide-derived complex 33 1.10: Spirocyclization of ester derivatives 33 2.1: Spirocyclizations from derivatives without direct connection to a ketone 51 2.2: Spirocyclizations of dienecarbinol derivatives 53 2.3: Addition of 3-buten-1-ylmagnesium bromide to aldehyde 2.42 58 2.4: Addition of 3-butenyl-1-ylmagnesium bromide to aldehyde 2.52 61 2.5: Cyclization attempt of acetyl-protected alcohol 2.58 under photothermal conditions 64 2.6: Attempted addition of (E/Z)-2.67 to aldehyde 2.42 66 2.7: Addition of Z-2.67 to aldehyde 2.42 67 2.8: Subjection of (4Z)-2.62 to cyclization under photothermal conditions 67 2.9: Addition of dienyl Grignard 2.72 to aldehyde 2.42 69 2.10: Unsuccessful attempt at tandem double cyclization of 2.69 70 3.1: Sodium borohydride reduction of acyclic ketone 3.5 96 3.2: Alkyllithium additions so acyclic ketone 3.7 96 3.3: Conformational equilibrium of acyclic ketone 3.9 96 3.4: Addition of 3-buten-1-ylmagnesium bromide to aldehyde 3.18 100 3.5: Addition of 3-buten-1-ylmagnesium bromide to aldehyde 3.24 102 3.6: Reaction of spirocycles 3.26 with CuCl2 104 – !vii – LIST OF SCHEMES Scheme 1-1: Difference between reaction of Me3NO and other reagents with methoxy- 11 substituted cyclohexadiene. Scheme 1-2: Total synthesis of trichodermol. 24 Scheme 1-3: Proposed synthesis of verrucarol via dienyl-Fe(CO)3 complex 1.100. 25 Scheme 1-4: Proposed mechanism for cyclization of 1.109a. 32 Scheme 2-1: Sketched approach to Verrucarol from ester 2.22. 52 Scheme 2-2: Alkyl and alkoxide additions to aldehyde 2.23. 52 Scheme 2-3: Synthesis towards methyl ester 2.34 via Michael-Wittig route. 55 Scheme 2-4: Synthetic route to ester 2.34 from benzoic acid. 56 Scheme 2-5: Attempt of formation of ester 2.34 via direct complexation of 2.37. 56 Scheme 2-6: Preparation of aldehyde 2.42 via Mukiayama oxidation. 57 Scheme 2-7: Conversion of regioisomers to aldehyde 2.42 under thermal conditions. 57 Scheme 2-8: Retrosynthetic approach to enone 2.48. 60 Scheme 2-9: Synthetic route to aldehyde 2.52 via Birch reduction of m-anisic acid. 61 Scheme 2-10: Conversion to conjugated and 2.50 from mixture of isomers under basic 61 conditions. Scheme 2-11: Possible depiction for the formation of ketone 2.56 63 Scheme 2-12: Protection of alcohol 2.54 with acetic anhydride and methyl iodide. 64 Scheme 2-13: Synthetic scheme towards synthesis of Grignard reagent (E/Z)-2.67. 65 Scheme 2-14: Synthesis of Grignard reagent 2.67 from cis-2.65. 66 Scheme 2-15: Synthetic scheme towards conjugated diene Grignard 2.72. 69 Scheme 4-1: Retrosynthetic approach to all-carbon spirocycle 4.1 117 – !viii – LIST OF FIGURES Figure 1-1: Examples of reactions involving iron carbonyl derivatives. 2 Figure 1-2: General examples of an acyclic and cyclic η4-(diene)tricarbonyliron derivatives. 2 Figure 1-3: Structures of Fe(CO)5, Fe2(CO)9 and Fe3(CO)12. 3 Figure 1-4: Examples of diene-rearrangements using Fe(CO)5 to form conjugated diene 4 complexes. Figure 1-5: Iron complexations using Fe2(CO)9 and Fe3(CO)13. 6 Figure 1-6: Examples of heterodiene-Fe(CO)3 complexes. 6 Figure 1-7: Iron complexations utilizing transfer agents. 7 Figure 1-8: Asymmetric iron complexations utilizing heterodiene-Fe(CO)3 derivatives as 8 transfer agents. Figure 1-9: Demetallations achieved with different oxidizing agents. 10 Figure 1-10: Reactions on diene-Fe(CO)3 substrates that demonstrate the protecting 13 capability of the Fe(CO)3 group. Figure 1-11: Diene protection from carbene additions. 13 Figure 1-12: Friedel-Crafts acylations of diene-Fe(CO)3 complexes. 14 Figure 1-13: Stabilization of reactive diradicals and carbocations via Fe(CO)3 16 complexation. Figure 1-14: Stereoselective additions to diene-Fe(CO)3 complexes. 18 Figure 1-15: Stereoselective Diels-Alder cycloadditions using diene-Fe(CO)3 complexes as 19 a source of diene or dienophile. Figure 1-16: Preparation of dienyl-Fe(CO)3 complexes via hydride abstraction. 20 Figure 1-17: Generic example of cyclohexadienyl-Fe(CO)3 complex. 21 Figure 1-18: Nucleophilic additions to generic methoxycyclohexadienyl-Fe(CO)3 22 derivatives. Figure 1-19: Product from reaction of 1.91 with strongly basic nucleophiles. 23 Figure 1-20: Radical dimerizations of dienyl-Fe(CO)3 complexes. 26 Figure 1-21: Mechanism of radical dimerization. 26 Figure 1-22: Attempts of intramolecular radical cyclocoupling reactions from dienyl-Fe(CO)3 27 substrates. Figure 1-23: Spirocyclization of amide diene-Fe(CO)3 complexes with pendant alkene 29 substitution. Figure 1-24: Pre- and post-cyclization rearrangements of diene-Fe(CO)3 complexes.
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