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ABSTRACT Title of Dissertation: DEVELOPMENT of ARYL ABSTRACT Title of Dissertation: DEVELOPMENT OF ARYL SILOXANE CROSS- COUPLING TECHNOLOGY AND ITS APPLICATION TO THE SYNTHESIS OF COLCHICINE AND ALLOCOLCHICINE DERIVATIVES William Michael Seganish, Doctor of Philosophy, 2005 Dissertation directed by: Professor Philip DeShong Department of Chemistry and Biochemistry One of the most versatile methods for the formation of aryl-aryl bonds is the palladium-catalyzed cross-coupling reaction. Previous work in the DeShong laboratory has demonstrated the utility of aryl siloxanes for the palladium-catalyzed cross-coupling of aryl iodides, bromides, and chlorides, as well as new synthetic methods for the formation of aryl siloxanes. The work reported herein details (1) the synthesis of aryl siloxanes using ortho-metallation techniques (2) the coupling of aryl bis(catechol) silicates with aryl triflates, and (3) the application of aryl siloxane coupling technology to the synthesis of colchicine and allocolchicine derivatives. The synthesis of aryl siloxanes had previously been performed using either metal-halogen exchange, or transition metal-catalyzed silylation. These techniques necessitate the use of an aryl halide as the starting material. The application of ortho- metallation conditions avoids this requirement and allows for the synthesis of siloxanes directly from the unfunctionalized arene. Using this approach, ortho-ether and carbamate siloxanes were prepared in good yields, however, o-benzamide siloxanes could not be prepared using this method. The coupling of aryl triflates with aryl siloxanes had previously proven problematic due to competitive hydrolysis of the triflate. The use of aryl bis(catechol) silicates as siloxane surrogates facilitated the coupling of aryl triflates and iodides bearing a range of functional groups in excellent yield. Additionally, aryl bromides could be successfully coupled by switching from conventional heating to microwave irradiation. The use of aryl siloxanes in the synthesis of the natural products colchicine and allocolchine was explored. It was found that the carbocyclic framework of colchicine could be constructed using an aryl siloxane coupling reaction; however, the reaction required the use of a stoichiometric amount of the palladium “catalyst.” This amount of catalyst was required because of the competition between a slow oxidative addition step, and a fast protodesilylation pathway that lead to the decomposition of the siloxane. The synthesis of the allocolchicine carbocyclic framework was successful utilizing a siloxane coupling reaction, and a phenanthrol ring expansion protocol as the key steps. DEVELOPEMENT OF ARYL SILOXANE CROSS-COUPLING TECHNOLOGY AND ITS APPLICATION TO THE SYTHESIS OF COLCHICINE AND ALLOCOLCHICINE DERIVATIVES By William Michael Seganish Dissertation submitted to the Faculty of the Graduate School of the University of Maryland, College Park in partial fulfillment of the requirements for the degree of Doctor of Philosophy 2005 Advisory Committee: Professor Philip DeShong, Chair Assistant Professor Douglas English Associate Professor Lyle Isaccs Professor Ian Mather (Animal and Avian Sciences) Professor Steve Rokita © Copyright by William Michael Seganish 2005 DEDICATION To my parents, Mike and Nancy, Sister Kate, Wife Jenny, And baby David ii ACKNOWLEDGEMENTS My sincerest gratitude goes to Phil, my advisor and mentor. It was he who made me the chemist I am today. Thanks for prodding me in the right direction and keeping me focused, especially toward the end. I am grateful to all the former and current members of the DeShong group, and to all of my friends in the department. You all have made Maryland an exciting and fun place to work and learn. I am thankful for the time that I had to spend here. Last, and certainly not least, I wish to thank my wife Jenny for putting up with me through these years of graduate school. Her constant support and encouragement made my difficult tasks and choices much easier to bear. iii TABLE OF CONTENTS List of Tables.....................................................................................................................vi List of Schemes................................................................................................................viii List of Abbreviations.........................................................................................................xii Chapter 1: The Development and Use of Palladium(0)-Catalyzed Coupling Reactions in the Synthesis of Biaryl Natural Products............................................1 Introduction..................................................................................................1 Stille Coupling.............................................................................................3 Suzuki Coupling..........................................................................................5 Hiyama Coupling.......................................................................................10 Conclusions................................................................................................18 Chapter 2: Application of Directed Ortho-Metallation Toward the Synthesis of Aryl Siloxanes................................................................................................................19 Introduction................................................................................................19 Mechanistic Studies.......................................................................21 O-Alkyl Directing Groups.............................................................24 Carbamate Directing Groups.........................................................26 Aniline and Nitrogen Directing Groups........................................29 Benzamide Directing Groups........................................................30 Application of Directed ortho-Metallation to the Synthesis of Aryl Siloxanes....................................................................32 Results and Discussion..............................................................................33 Conclusions................................................................................................43 Experimental Section.................................................................................44 General Experimental....................................................................44 Synthesis of Starting Materials......................................................46 Synthesis of Aryl Siloxanes...........................................................48 Representative Procedure for the Palladium-Catalyzed Cross Coupling of Aryl Siloxanes with Aryl Bromides..............53 Representative Procedure for the Synthesis of Aryl Siloxanes Using Triethoxysilyltriflate................................................55 Representative Procedure for the Synthesis of Aryl Siloxanes Using Silicon Tetrachloride...............................................56 Chapter 3: Preparation and Palladium-Catalyzed Cross-Coupling of Aryl Triethylammonium (Bis)catechol Silicates With Aryl Halides And Triflates.......57 Part 1. Cross-Coupling of Aryl (Bis)catechol Silicates with Aryl Triflates..............................................................................57 Introduction....................................................................................57 Synthesis and Structure of (Bis)catechol Silicates.............57 Reaction of (Bis)catechol Silicates with Strong Nucleophiles..........................................................60 iv Use of (Bis)catechol Silicates for the Allylation of Aldehydes..............................................................60 Use of (Bis)catechol Silicates in Palladium-Catalyzed Cross-Coupling Reactions.....................................61 Palladium-Catalyzed Cross-Coupling Methodologies......62 Results and Discussion..................................................................64 Conclusion.....................................................................................80 Part 2. Palladium-Catalyzed Cross-Coupling of Aryl Triethylammonium (Bis)catechol Silicates with Aryl Bromides Using Microwave Irradiation.......................................................81 Introduction....................................................................................81 Microwave Effects in Chemical Reactions........................81 Synthetic Applications.......................................................82 Cross-Coupling of Aryl Bromides with Aryl (Bis)catechol Silicates............................................84 Results and Discussion..................................................................85 Conclusions and Outlook...............................................................90 Part 3. Experimental Section.....................................................................91 General Experimental....................................................................91 Synthesis and Characterization of Aryl (Bis)catechol Silicates....93 General Procedure for the Synthesis and Characterization of Aryl Triflates......................................................................99 General Procedure for the Cross-Coupling of Aryl (Bis)catechol Silicates with Aryl Triflates.......................108 General Procedure for the Cross-Coupling of Aryl (Bis)catechol Silicates with Aryl Bromdies Using Microwave Irradiation.....................................................117 Chapter 4: Application of Aryl Siloxane Cross-Coupling Technology to the
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