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Synthetic and Structural Studies of Phenylenes and Dehydrobenzannulenes

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Synthetic and Structural Studies of Phenylenes and Dehydrobenzannulenes Synthetic and Structural Studies of Phenylenes and Dehydrobenzannulenes by Ognjen Scepan Miljanic Diploma (University of Belgrade) 2000 A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Chemistry in the GRADUATE DIVISION of the UNIVERSITY OF CALIFORNIA, BERKELEY Committee in charge: Professor K. Peter C. Vollhardt, Chair Professor Robert G. Bergman Professor Ronald Gronsky Fall 2005 The dissertation of Ognjen Scepan Miljanic is approved: Chair Date Date Date University of California, Berkeley Fall 2005 Synthetic and Structural Studies of Phenylenes and Dehydrobenzannulenes Copyright 2005 by Ognjen Scepan Miljanic Abstract Synthetic and Structural Studies of Phenylenes and Dehydrobenzannulenes by Ognjen Scepan Miljanic Doctor of Philosophy in Chemistry University of California, Berkeley Professor K. Peter C. Vollhardt, Chair This dissertation documents the findings on the syntheses of larger dehydrobenzannulenes and [ N]phenylenes and the exploration of their physical and chemical properties. Chapter One. This chapter summarizes the previous synthetic work on [N]phenylenes. Their structural, magnetic, and energetic properties, as well as chemical reactivity are reviewed, and comparisons are made between different phenylene topologies. Chapter Two. The synthesis of syn-doublebent [5]phenylene is presented. Approaches to three novel phenylenes, U-shaped [7]- and [9]phenylenes and C-shaped [7]phenylene are also discussed. Chapter Three. The topic of this chapter is the development of a novel alkyne metathesis-based route to ortho-dehydrobenzannulenes. Additionally, the application of microwave irradiation to Sonogashira couplings with gaseous propyne is described. Chapter Four. A versatile synthetic route based on a sequence of Sonogashira couplings is described to access substituted dehydrobenzannulenes. CpCo-mediated 1 cycloisomerizations of these materials that produced partially cyclized phenylenes are summarized. Chapter Five. The finding that dehydrobenzannulenes substituted with sufficiently bulky silyl-groups are conformationally locked at ambient temperatures is presented. This result inspired the synthesis of the first chiral diphenylacetylene. Variable-temperature NMR studies of both of these systems were undertaken to determine the corresponding racemization barriers. Chapter Six. The final chapter details the experimental procedures of the studies presented in Chapters 2–5. 2 to Peace i Table of Contents Chapter One [N]Phenylenes: a Novel Class of Cyclohexatrienoid Hydrocarbons 1.1 Introduction.........................................................................................................1 1.2 Preparation of Phenylenes...................................................................................9 1.2.1 Early Synthetic Strategies........................................................................... 9 1.2.2 Syntheses of New Phenylenes................................................................... 15 1.2.2.1 Angular and Helical Phenylenes........................................................... 15 1.2.2.2 Zigzag Phenylenes ................................................................................ 19 1.2.2.3 Phenylenes with Mixed Topology: the “Bent” Isomers........................ 22 1.2.2.4 Branched Phenylenes............................................................................ 27 1.2.2.5 Circular Phenylenes .............................................................................. 31 1.3 Comparative Reactivity of the Phenylenes....................................................... 34 1.3.1 Hydrogenation...........................................................................................34 1.3.2 Oxacyclopropanation and Cyclopropanation............................................ 37 1.3.3 [4+2]Cycloadditions.................................................................................. 41 1.3.4 Flash Vacuum Pyrolysis............................................................................ 46 1.3.5 Interaction with Organometallic Fragments.............................................. 48 1.4 Physical Properties of the Phenylenes .............................................................. 52 1.4.1 Structural Properties.................................................................................. 52 1.4.2 Magnetic Properties .................................................................................. 63 1.4.3 Energetic Properties.................................................................................. 67 1.5 Thesis Summary................................................................................................72 ii Chapter Two Synthetic Approaches to Novel Phenylenes with Mixed Angular and Linear Fusion 2.1 Introduction.......................................................................................................73 2.2 Retrosynthetic Approach to 60 , 118 , 119 , and 120 ........................................... 76 2.3 Synthesis of Doublebent [5]Phenylene 60 ........................................................ 78 2.4 Attempted Synthesis of C-Shaped [7]Phenylene ( 118 ) ....................................82 2.5 Attempted Syntheses of U-Shaped [7]Phenylene ( 119 ).................................... 84 2.5.1 Intramolecular Approach .......................................................................... 84 2.5.2 Intermolecular Approach .......................................................................... 90 2.6 Attempted Synthesis of U-Shaped [9]Phenylene ( 120 ) ....................................92 2.7 Calculated and Measured Properties of 60 , 118 , 119 , and 120 ......................... 94 2.8 Summary.........................................................................................................102 Chapter Three A Novel Alkyne Metathesis-Based Route to Dehydrobenz- annulenes 3.1 Introduction.....................................................................................................103 3.2 Retrosynthetic Approach to Dehydrobenzannulenes...................................... 105 3.3 Preparation of Iodinated Precursors................................................................ 110 3.4 Classical and Microwave-Assisted Propynylations ........................................ 112 3.5 Dehydrobenzannulenes by Alkyne Metathesis............................................... 115 3.6 Properties of Novel Dehydrobenzannulenes................................................... 119 3.7 Summary.........................................................................................................121 iii Chapter Four Synthesis of Octaalkynylated Dehydrobenz[18]annulenes and Attempted Cycloisomerization into Circular [8]Phenylene and Derivatives 4.2 Retrosynthetic Analysis of Circular [8]Phenylene.......................................... 126 4.3 Previous Attempts to Synthesize Circular [8]Phenylene ................................129 4.4 Synthesis and Properties of Octaalkynylated Dehydrobenz[18]annulenes 156 and 171b–c..................................................................................................................133 4.5 Attempted Cycloisomerization of 156 and 171b-c into Circular [8]Phenylenes 121 and 170b-c............................................................................................................ 137 4.6 Properties of Novel Phenylenes...................................................................... 142 4.7 Summary and Future Directions ..................................................................... 143 Chapter Five Consequences of Steric Crowding Around Triple Bonds in Acyclic and Cyclic Systems 5.1 Introduction.....................................................................................................144 5.2 Previous Examples of Hindered Rotation in Phenylene Precursors ...............149 5.3 Synthesis and Properties of the First Chiral 2,2’,6,6’-Tetrakisalkynyl Diphenylacetylene.......................................................................................................151 5.4 Stereochemical Properties of 171c ..................................................................154 5.5 Proposed Mechanism of Interconversion between the Conformers of 171c .. 159 5.6 Summary and Future Directions ..................................................................... 174 Chapter Six Experimental and Computational Details 6.1 General Considerations...................................................................................175 iv 6.2 Experiments and Calculations Related to Chapter 2....................................... 177 6.2.1 Calculated Structures of 60 and 118–120 ............................................... 203 6.3 Experiments Related to Chapter 3 .................................................................. 209 6.3.1 Crystallographic Information for 159 ..................................................... 226 6.4 Experiments Related to Chapter 4 .................................................................. 231 6.4.1 Calculated Structures of 121 , 156 , and 191–195 .................................... 254 6.5 Experiments Related to Chapter 5 .................................................................. 276 6.5.1 Calculated Structures of Transition States for the Inversion of 171c and 213–216 .................................................................................................................280 v Abbreviations and Acronyms 2D two dimensional
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