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From Α-Carbonyl Bicyclic Furans to Expanded Chiral Hexa-Peri-Hexabenzocoronenes

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From Α-Carbonyl Bicyclic Furans to Expanded Chiral Hexa-Peri-Hexabenzocoronenes University of Nevada, Reno Alkyne Cyclizations: From α-Carbonyl Bicyclic Furans to Expanded Chiral Hexa-peri-hexabenzocoronenes A dissertation submitted in partial fulfillment of the Requirements for the degree of Doctor of Philosophy in Chemistry by Khagendra B. Hamal Dr. Wesley. A. Chalifoux/Dissertation Advisor May 2018 Copyright by Khagendra B. Hamal 2018 All Rights Reserved THE GRADUATE SCHOOL We recommend that the dissertation prepared under our supervision by KHAGENDRA B. HAMAL Entitled Alkyne Cyclizations: From α-Carbonyl Bicyclic Furans to Expanded Chiral Hexa-peri-hexabenzocoronenes be accepted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Wesley A. Chalifoux, Ph.D., Advisor Robert S. Sheridan, Ph.D., Committee Member Benjamin. T. King, Ph.D., Committee Member Ravi Subramanian, Ph.D., Committee Member Mark A. Pinsky, Ph.D., Graduate School Representative David W. Zeh, Ph. D., Dean, Graduate School May, 2018 i Abstract The development and utilization of highly functionalized and reactive dienophiles in the Diels–Alder cyclization reaction is of value in producing diversely functionalized, and therefore useful, cyclic products. We have developed a Diels–Alder reaction of conjugated 2,4-diynones, promoted by Lewis acids (Me2AlCl or EtAlCl2), to produce substituted 2- alkynyl-1,4-cyclohexadiene (‘skipped’ cyclohexadiene) products in good to excellent yields. The reaction was successful with a variety of cyclic and acyclic dienes as well as with a diversity of 2,4-diynones. The diversely functionalized 1,4-cyclohexadiene products that are obtained from this reaction are of utility as intermediates on the way to synthesizing pharmaceutically relevant cyclic and polycyclic compounds. Those heavily functionalized skipped dienes were cleanly converted into dihydroisobenzofuran (bicyclic furan) derivatives in the presence of π-Lewis acid catalysts. Ketone derivatives were obtained by using CuCl2 as catalyst whereas AgNO3 provides aldehyde analogues. We have also demonstrated a facile one-pot approach to construct bicyclic furan derivatives directly from diynone and diene starting materials. We also describe the synthesis, characterization, structure and properties of expanded chiral hexa-peri-hexabenzocoronenes. The Suzuki cross-coupling between bromo substituted hexa-peri-hexabenzocoronene and diynylphenyl borate gives the coupled product. The alkyne benzannulation reaction of coupled product promoted by a mixture of TFA and TfOH afforded the desired final product. The twisted structure of chiral compounds is unambiguously confirmed by X-ray crystallographic analysis and the enantiomers are separated in chiral HPLC. ii iii Dedication I dedicate this dissertation to my parents (Beni Khanal & Mata Khanal) for their never-ending love and support. iv Acknowledgements I would like to express the deepest appreciation to my advisor, Dr. Wesley A. Chalifoux, for his willingness and enthusiasm in allowing and helping me to grow my chemical knowledge and skillset. I would also like to thank Dr. Chalifoux for always holding the bar high and helping me to become the researcher that I am today. Without his guidance and persistent help this dissertation would not have been possible. I would like to thank my committee members, Dr. Robert S. Sheridan, Dr. Benjamin T. King, Dr. Ravi Subramanian, and Dr. Mark A. Pinsky for their guidance, time, and support. I would also like to thank Dr. Vincent Catalano and Dr. Stephen Spain for instrumentation training and assistance. I would like to thank my lab mates in the Chalifoux lab, particularly Michael Walley, Vivek Aryal and Paban Sitaula for their help and support. I would also like to thank the faculty, staff, and students in the UNR Chemistry department for helpful discussions and assistance. I would also like to thank my friends and family for always lending an ear and their support when I needed it most. I would like to thank my parents, whose love and guidance are with me in whatever I pursue. They are the ultimate role models. Most importantly, I wish to thank my loving and supportive wife, Parmila, and my two wonderful daughters, Crystal and Khusi, who provide unending inspiration. v Table of Contents 1 Introduction …………………………………………………………………………….1 1.1. The Diels-Alder Cycloaddition ………………………………………………….1 1.2. Alkyne Cyclizations……………………………………………………………...4 1.3. One-pot Reactions………………………………………………………………..6 1.4. Alkyne Benzannulations………………………………………………………....8 1.5. Conclusions……………………………………………………………………...10 1.6. References……………………………………………………………………….11 2 Synthesis of 2-Alkynyl-1,4-cyclohexadienes via a Diels-Alder Reaction of Conjugated 2,4-Diynones……………………………………………………………………………..13 2.1 Introduction………………………………………………………………………13 2.2 Double Diels-Alder Reaction of Conjugated 2,4-Diynones………………….….16 2.3 Regioselective Diels-Alder Reaction of Conjugated 2,4-Diynones…………......22 2.4 Conclusion…………………………………………………………………...…..29 2.5 Experimental……………………………………………………………………..30 2.6 References………………………………………………………………………..46 3 One-Pot Synthesis of α-Carbonyl Bicyclic Furans via a Sequential Diels-Alder/5-Exo- Dig Cyclization/Oxidation Reaction……………………………………………………..48 3.1 Introduction………………………………………………………………..……..48 3.2 Copper(II)-Catalyzed Synthesis of α-Carbonyl Bicyclic Furans………….……..50 3.3 One-Pot Synthesis of α-Carbonyl Bicyclic Furans……………………………....56 3.4 Silver-catalyzed Synthesis of Dihydroisobenzofuran Carboxaldehyde Derivatives via a One-Pot Protodesilylation/Cyclization/Oxidation Reaction……………………….60 vi 3.5 Conclusion……………………………………………………………………….65 3.6 Experimental…………………………………………………………………..…66 3.7 References…………………………………………………………………….....102 4 Synthesis of Expanded Hexa-peri-hexabenzocoronenes by Two and Four-fold Alkyne Benzannulation Reaction……………………………………………………..………...104 4.1 Introduction……………………………………………………………………...104 4.2 Target HBC Molecules and Retrosynthesis……………………………………..105 4.2.1 Synthesis of Diynylphenyl Borate……………………………..…………….107 4.2.2 Synthesis of Hexa-peri-hexabenzocoronenes……………………….………108 4.2.3 Synthesis of Final Product ………………………………………………….111 4.2.4 X-ray Crystallography……………………………………………………....114 4.3 Four-fold Alkyne Benzannulation……………………………………………….115 4.3.1 Possible Isomers of Compound 4.32………………………………………...120 4.3.2 Reason for the formation of Isomers D and E…….………...……………….122 4.4 Conclusion……………………………………………………………………….124 4.5 Experimental……………………………………………………………………..124 4.6 References……………………………………………………………………..…134 5 Supporting Information (Appendix)………………………………………………..…136 vii List of Tables Table 2-1: Preliminary screening of Lewis acids for the double Diels-Alder reaction…17 Table 2-2: Thermal cycloaddition reaction between diynone 2.3a and diene 2.4a……..18 Table 2-3: Preliminary screening of dienes with diynone 2.1a……………………..…..19 Table 2-4: Screening of solvent in double Diels-Alder reaction to improve diastereoselectivity………………………………………………………………………21 Table 2-5: Lewis acid screening for Diels-Alder reaction between diynone 2.3a and diene 2.4a……………………….……………………………………………………….24 Table 2-6: Diynone scope for the Diels-Alder reaction with 2.2a…………………..….25 Table 2-7: Diene scope for the Diels-Alder reaction with 2.3a ………………..………27 Table 3-1: Screening of various commercial copper catalysts ……………….………...51 Table 3-2: Substrate scope……………………………………………………………....54 Table 3-3: Crystal parameters and refinement metrics of compound 3.3p……………..55 Table 3-4: Diynone scope for one-pot reaction………………………………………....57 Table 3-5: Copper-catalyzed diene scope for one-pot reaction………………………....58 Table 3-6: Silver-catalyzed diene scope for one-pot reaction………………………......62 Table 4-1: Crystal parameters and refinement metrics of compound 4.21c…………...114 viii List of Figures Figure 1-1: Diels-Alder reaction between 1.1 and 1.2 to form six-membered ring 1.3....1 Figure 1-2: Patterns of cyclization for 3-to 6-membered rings. Reactions predicted to be favorable by Baldwin are boxed………………………………………………………....5 Figure 3.1: Selected biologically active molecules containing an α-carbonyl dihydroisobenzofuran moiety……………………………………………………………48 Figure 3-3: Single crystal X-ray structure of compound 3.3p (50% probability). Crystals suitable for single-crystal X-ray diffraction were obtained by slow evaporation of a solution of 3.3p in dichloromethane……………….…………………………………….57 Figure 4-1: Hexa-peri-hexabenzocoronenes (HBCs) with/without bromo substituents......................................................................................................................104 Figure 4-2: Expanded hexa-peri-hexabenzocoronenes (our target compounds)……...105 Figure 4-3: Retrosynthetic analysis of compound 4.4 leading to the precursors 4.2a and 4.7……………………………………………………………………………………...106 Figure 4-4: Chiral HPLC traces of compound 4.21c....................................................114 Figure 4-5: Single crystal X-ray structure of compound 4.21c.……………………...114 Figure 4-6: All the possible isomers of compound 4.32……………………………...121 Figure 4-7: Explanation for the formation of isomers D and E……………………....123 ix List of Schemes Scheme 1-1: Diels-Alder cyclization of ynone 1.4 vs enone 1.6 as dienophile………..2 Scheme 1-2: Birch reduction of arenes 1.8 and 1.10…………………………………..3 Scheme 1-3: Diels-Alder cyclization of diynone 1.12 with diene 1.13 to get 1.14……3 Scheme 1-4: Synthesis of oxygen heterocycle by electrophilic cyclization of acetylenic aldehyde………………………………………………………………………………..6 Scheme 1-5: Cu-catalyzed cascade synthesis of substituted furan derivatives………..7 Scheme 1-6:
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